Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Each subframe (sent every six seconds) has the *GPS Time*. The GPS/UTC offset is only sent in subframe 4 of page 18 of the almanac data, i.e. once every 12.5 minutes. Also, a comment on the ZDA message mentioned previously. I had tried that as part of my project RD and it also returns best guess UTC, just like RMC. i.e. if the receiver hasn't received the GPS/UTC offset, it doesn't actually report UTC. On 25 April 2012 19:22, StarTraX gpsanima...@gmail.com wrote: I've been reading up on the GPS signal structure, and it's true that it takes 12 1/2 minutes for the full sequence, but... and this is a big but... the GPS time and GPS/UTC offset are sent with every sub frame, and they come by every six seconds. So you can forget about waiting 12 1/2 minutes. before being certain of the time! It's synchronized every 6 seconds. Its all well explained in Wikipedia http://en.wikipedia.org/wiki/GPS_signals -- Andrew -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Hi, The RMC message contains a status parameter, this is either V=data not valid or A=data valid. You need to wait until you read an A in the RMC, before this you will not get a ZDA message even if you have enabled it. To enable RMC messages: $PSRF103,04,00,01,01 Once you get an A in the RMC message you should then enable ZDA messages: $PSRF103,08,00,01,01 You will need to calculate and append checksum to the enable messages which I haven't done. The ZDA message contains a UTC time, also day, month and year, local time offsets to UCT are also included. The time is the details the 1PPS pulse that has just occurred. On Wed, Apr 25, 2012 at 6:44 AM, StarTraX gpsanima...@gmail.com wrote: Yes I do and will give it a go. Ta. On Wednesday, April 25, 2012 3:01:33 PM UTC+10, andrewg_oz wrote: 1300ms ahead sounds odd. If it was behind I'd say it was just a reporting delay as part of the usual message processing, but ahead is weird. It's not GPS, but if you have an Internet connection, what about querying an NTP server? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -- http://about.me/SPlatten -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Further, here are the sentence types I do get: GPGSA, GPGGA, GPGLL, GPRMC, GPGSV, GPVTG. The SiRF manual indicates the ZDA message is only provided to the GSW2 software versions 2.3.2 and above - maybe that's not being implemented on the phones. On Wednesday, April 25, 2012 3:43:34 PM UTC+10, StarTraX wrote: Hi Sy, Thanks for your input. If I understand you correctly, you are suggesting I look for a $GPZDA NMEA sentence. I have just checked the SiRF NMEA Manual and tried it. I'm getting RMC and GGA but no ZDA sentences on either my SGS 11 or HTC , both running 2.3.3. Am I missing something here? On Wednesday, April 25, 2012 3:13:46 PM UTC+10, Sy wrote: You need to enable RMC messages and then wait for a GPS lock, then enable ZDA messages these give a 1PPS message with a timestamp accurate to 1ms. On Apr 25, 2012 6:02 AM, Andrew Gregory andrew.greg...@gmail.com wrote: 1300ms ahead sounds odd. If it was behind I'd say it was just a reporting delay as part of the usual message processing, but ahead is weird. It's not GPS, but if you have an Internet connection, what about querying an NTP server? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
If ZDA isn't implemented or supported then you are really out of luck as the time from the GPS could be out significantly also add to that the lag in sending and receiving the NMEA message. We use the 1PPS pulse at work to synchronise remote devices in the field, once we lock on with the RMC the 1PPS pulse is used to generate an interrupt which ensures that devices are absolutely in sync. On Wed, Apr 25, 2012 at 8:39 AM, StarTraX gpsanima...@gmail.com wrote: Further, here are the sentence types I do get: GPGSA, GPGGA, GPGLL, GPRMC, GPGSV, GPVTG. The SiRF manual indicates the ZDA message is only provided to the GSW2 software versions 2.3.2 and above - maybe that's not being implemented on the phones. On Wednesday, April 25, 2012 3:43:34 PM UTC+10, StarTraX wrote: Hi Sy, Thanks for your input. If I understand you correctly, you are suggesting I look for a $GPZDA NMEA sentence. I have just checked the SiRF NMEA Manual and tried it. I'm getting RMC and GGA but no ZDA sentences on either my SGS 11 or HTC , both running 2.3.3. Am I missing something here? On Wednesday, April 25, 2012 3:13:46 PM UTC+10, Sy wrote: You need to enable RMC messages and then wait for a GPS lock, then enable ZDA messages these give a 1PPS message with a timestamp accurate to 1ms. On Apr 25, 2012 6:02 AM, Andrew Gregory andrew.greg...@gmail.com wrote: 1300ms ahead sounds odd. If it was behind I'd say it was just a reporting delay as part of the usual message processing, but ahead is weird. It's not GPS, but if you have an Internet connection, what about querying an NTP server? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@** googlegroups.com android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+**unsubscr...@googlegroups.comandroid-developers%2bunsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/**group/android-developers?hl=enhttp://groups.google.com/group/android-developers?hl=en -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -- http://about.me/SPlatten -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Sy. Now you've got me really confused! I don't understand ..*sending*... the NMEA message. In my code I'm just listening for the NMEA sentence in an NMEA listener. There's no sending involved here is there? On what sort of device are your receiving the ZDA sentence? On Wednesday, April 25, 2012 5:43:23 PM UTC+10, Sy wrote: If ZDA isn't implemented or supported then you are really out of luck as the time from the GPS could be out significantly also add to that the lag in sending and receiving the NMEA message. We use the 1PPS pulse at work to synchronise remote devices in the field, once we lock on with the RMC the 1PPS pulse is used to generate an interrupt which ensures that devices are absolutely in sync. On Wed, Apr 25, 2012 at 8:39 AM, StarTraX gpsanima...@gmail.com wrote: Further, here are the sentence types I do get: GPGSA, GPGGA, GPGLL, GPRMC, GPGSV, GPVTG. The SiRF manual indicates the ZDA message is only provided to the GSW2 software versions 2.3.2 and above - maybe that's not being implemented on the phones. On Wednesday, April 25, 2012 3:43:34 PM UTC+10, StarTraX wrote: Hi Sy, Thanks for your input. If I understand you correctly, you are suggesting I look for a $GPZDA NMEA sentence. I have just checked the SiRF NMEA Manual and tried it. I'm getting RMC and GGA but no ZDA sentences on either my SGS 11 or HTC , both running 2.3.3. Am I missing something here? On Wednesday, April 25, 2012 3:13:46 PM UTC+10, Sy wrote: You need to enable RMC messages and then wait for a GPS lock, then enable ZDA messages these give a 1PPS message with a timestamp accurate to 1ms. On Apr 25, 2012 6:02 AM, Andrew Gregory andrew.greg...@gmail.com wrote: 1300ms ahead sounds odd. If it was behind I'd say it was just a reporting delay as part of the usual message processing, but ahead is weird. It's not GPS, but if you have an Internet connection, what about querying an NTP server? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@** googlegroups.com android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+**unsubscr...@googlegroups.comandroid-developers%2bunsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/**group/android-developers?hl=enhttp://groups.google.com/group/android-developers?hl=en -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -- http://about.me/SPlatten -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Sorry, you are quite correct, I'm working with lots of protocols, a lot of which are polled, sorry for the confusion, you do just listen for and receive an NMEA message. The only sending involved is to enable specific messages. Our GPS receivers are embedded devices, I'm not absolutely sure of the part no. but the ZDA message is well document in the NMEA specification. On Wed, Apr 25, 2012 at 9:04 AM, StarTraX gpsanima...@gmail.com wrote: Sy. Now you've got me really confused! I don't understand ..*sending*... the NMEA message. In my code I'm just listening for the NMEA sentence in an NMEA listener. There's no sending involved here is there? On what sort of device are your receiving the ZDA sentence? On Wednesday, April 25, 2012 5:43:23 PM UTC+10, Sy wrote: If ZDA isn't implemented or supported then you are really out of luck as the time from the GPS could be out significantly also add to that the lag in sending and receiving the NMEA message. We use the 1PPS pulse at work to synchronise remote devices in the field, once we lock on with the RMC the 1PPS pulse is used to generate an interrupt which ensures that devices are absolutely in sync. On Wed, Apr 25, 2012 at 8:39 AM, StarTraX gpsanima...@gmail.com wrote: Further, here are the sentence types I do get: GPGSA, GPGGA, GPGLL, GPRMC, GPGSV, GPVTG. The SiRF manual indicates the ZDA message is only provided to the GSW2 software versions 2.3.2 and above - maybe that's not being implemented on the phones. On Wednesday, April 25, 2012 3:43:34 PM UTC+10, StarTraX wrote: Hi Sy, Thanks for your input. If I understand you correctly, you are suggesting I look for a $GPZDA NMEA sentence. I have just checked the SiRF NMEA Manual and tried it. I'm getting RMC and GGA but no ZDA sentences on either my SGS 11 or HTC , both running 2.3.3. Am I missing something here? On Wednesday, April 25, 2012 3:13:46 PM UTC+10, Sy wrote: You need to enable RMC messages and then wait for a GPS lock, then enable ZDA messages these give a 1PPS message with a timestamp accurate to 1ms. On Apr 25, 2012 6:02 AM, Andrew Gregory andrew.greg...@gmail.com wrote: 1300ms ahead sounds odd. If it was behind I'd say it was just a reporting delay as part of the usual message processing, but ahead is weird. It's not GPS, but if you have an Internet connection, what about querying an NTP server? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@** googlegroup**s.com android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+**unsubscribe**@googlegroups.comandroid-developers%2bunsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/**group**/android-developers?hl=enhttp://groups.google.com/group/android-developers?hl=en -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@** googlegroups.com android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+**unsubscr...@googlegroups.comandroid-developers%2bunsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/**group/android-developers?hl=enhttp://groups.google.com/group/android-developers?hl=en -- http://about.me/SPlatten -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -- http://about.me/SPlatten -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Yeah, I'm pretty sure you can't send commands to the Android GPS device. You'd probably need to be root and figure out the underlying device. -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
I've been reading up on the GPS signal structure, and it's true that it takes 12 1/2 minutes for the full sequence, but... and this is a big but... the GPS time and GPS/UTC offset are sent with every sub frame, and they come by every six seconds. So you can forget about waiting 12 1/2 minutes. before being certain of the time! It's synchronized every 6 seconds. Its all well explained in Wikipedia http://en.wikipedia.org/wiki/GPS_signals On Monday, April 23, 2012 5:47:21 PM UTC+10, andrewg_oz wrote: Some of the time confusion arises because GPS units can report a variety of GPS Time, UTC and semi-corrected GPS Time. I discovered this when building a precision timer for an industrial corrosion monitoring device. On startup the GPS would report UTC plus one second. Within 12.5 minutes it would report exactly UTC, i.e. after reception of the GPS/UTC correction factor. I could only assume that the GPS developers had pre-programmed in the UTC/GPS clock offset that was current when the device was manufactured. Since then a UTC leap second had been added. Importantly, there is no way to tell which of those times the GPS is reporting. No doubt the precise behavior varies from chipset to chipset. For my project I was using a SiRF III receiver and could switch on the raw 50bps data steam and watch for the GPS/UTC correction to be sure when I had UTC time. AFAIK, there is no way of doing that on Android, so for truly accurate times your best bet is to leave the GPS on for 12.5 minutes before reading the time, and hope that it has successfully received the clock correction. -- Andrew On Monday, April 23, 2012 5:47:21 PM UTC+10, andrewg_oz wrote: Some of the time confusion arises because GPS units can report a variety of GPS Time, UTC and semi-corrected GPS Time. I discovered this when building a precision timer for an industrial corrosion monitoring device. On startup the GPS would report UTC plus one second. Within 12.5 minutes it would report exactly UTC, i.e. after reception of the GPS/UTC correction factor. I could only assume that the GPS developers had pre-programmed in the UTC/GPS clock offset that was current when the device was manufactured. Since then a UTC leap second had been added. Importantly, there is no way to tell which of those times the GPS is reporting. No doubt the precise behavior varies from chipset to chipset. For my project I was using a SiRF III receiver and could switch on the raw 50bps data steam and watch for the GPS/UTC correction to be sure when I had UTC time. AFAIK, there is no way of doing that on Android, so for truly accurate times your best bet is to leave the GPS on for 12.5 minutes before reading the time, and hope that it has successfully received the clock correction. -- Andrew -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Thanks for your input to this, it's spurred me to further study. Re the GpsStatus object, that's a great suggestion but for the life of me, I can't get my SGS 11 to trigger the onStatusChanged event or to get anything from the GpsStatus object, so that's a bit annoying. But I'll press on. Despite monitoring for in excess of 12.5 minutes, the GPS time being reported in the NMEA string and Location.getTime are consistently slightly more than 1 second ahead of UTC - averages around 1300 ms. Odd eh? On Monday, April 23, 2012 8:01:25 PM UTC+10, andrewg_oz wrote: I've not looked at the relevant Android API before, but I would imagine that if you get a GpsStatus object from the LocationManager, then check each satellite for hasAlmanac(), then you might be more likely to have the correct GPS/UTC offset. It is still possible to have received the almanac data for all satellites in view, but still not received the GPS/UTC offset, so not a perfect solution. -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
1300ms ahead sounds odd. If it was behind I'd say it was just a reporting delay as part of the usual message processing, but ahead is weird. It's not GPS, but if you have an Internet connection, what about querying an NTP server? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
You need to enable RMC messages and then wait for a GPS lock, then enable ZDA messages these give a 1PPS message with a timestamp accurate to 1ms. On Apr 25, 2012 6:02 AM, Andrew Gregory andrew.greg...@gmail.com wrote: 1300ms ahead sounds odd. If it was behind I'd say it was just a reporting delay as part of the usual message processing, but ahead is weird. It's not GPS, but if you have an Internet connection, what about querying an NTP server? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Hi Sy, Thanks for your input. If I understand you correctly, you are suggesting I look for a $GPZDA NMEA sentence. I have just checked the SiRF NMEA Manual and tried it. I'm getting RMC and GGA but no ZDA sentences on either my SGS 11 or HTC , both running 2.3.3. Am I missing something here? On Wednesday, April 25, 2012 3:13:46 PM UTC+10, Sy wrote: You need to enable RMC messages and then wait for a GPS lock, then enable ZDA messages these give a 1PPS message with a timestamp accurate to 1ms. On Apr 25, 2012 6:02 AM, Andrew Gregory andrew.greg...@gmail.com wrote: 1300ms ahead sounds odd. If it was behind I'd say it was just a reporting delay as part of the usual message processing, but ahead is weird. It's not GPS, but if you have an Internet connection, what about querying an NTP server? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Yes I do and will give it a go. Ta. On Wednesday, April 25, 2012 3:01:33 PM UTC+10, andrewg_oz wrote: 1300ms ahead sounds odd. If it was behind I'd say it was just a reporting delay as part of the usual message processing, but ahead is weird. It's not GPS, but if you have an Internet connection, what about querying an NTP server? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Check out my new Examine GPS times
https://play.google.com/store/apps/details?id=com.gpsanimator.gpsTimerDisplayfeature=search_result#?t=W251bGwsMSwyLDEsImNvbS5ncHNhbmltYXRvci5ncHNUaW1lckRpc3BsYXkiXQ..free
app that displays both GPS times and System time.
On Monday, April 23, 2012 7:52:09 AM UTC+10, StarTraX wrote:
I could probably knock you up one quite quickly as I'm currently spending
a lot of time in that space. Could you be more specific about your
requirements? Maybe communicate directly with me through the info {at}
gpsanimator {dot} com
On Mon, Apr 23, 2012 at 12:00 AM, Panam pandem...@googlemail.com wrote:
Just to let you know, I am currently experimenting with GPS on a S Galaxy
I whose GPS is off about 24 hs in the future (+-some seconds) and it does
not seem to depend on the system time (adjusted the system time by some
minutes without effects). This seems to be a systematic error.
Btw. does somebody know an free app that shows the GPS time + date?
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Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Some of the time confusion arises because GPS units can report a variety of GPS Time, UTC and semi-corrected GPS Time. I discovered this when building a precision timer for an industrial corrosion monitoring device. On startup the GPS would report UTC plus one second. Within 12.5 minutes it would report exactly UTC, i.e. after reception of the GPS/UTC correction factor. I could only assume that the GPS developers had pre-programmed in the UTC/GPS clock offset that was current when the device was manufactured. Since then a UTC leap second had been added. Importantly, there is no way to tell which of those times the GPS is reporting. No doubt the precise behavior varies from chipset to chipset. For my project I was using a SiRF III receiver and could switch on the raw 50bps data steam and watch for the GPS/UTC correction to be sure when I had UTC time. AFAIK, there is no way of doing that on Android, so for truly accurate times your best bet is to leave the GPS on for 12.5 minutes before reading the time, and hope that it has successfully received the clock correction. -- Andrew -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Hey Andrew - what interesting revelations! What's the story behind the 12.5 minutes wait - is there some time offset update in the GPS signal? Where can I go to learn more? I'm now getting some very interesting results from my little app (above). When first receiving a signal, it's reporting a NMEA time with odd milliseconds, but after a variable time - between around 3 and I5 seconds, the NMEA time decimals go to zero and the time syncs with the location.getTime() value. I have discovered that my SGS 11 uses the SiRF Star IV chip. I'm keen to understand more - please point me to some reading, I have spent the day googling variations on GPS message syntax with no success. Cheers On Monday, April 23, 2012 5:47:21 PM UTC+10, andrewg_oz wrote: Some of the time confusion arises because GPS units can report a variety of GPS Time, UTC and semi-corrected GPS Time. I discovered this when building a precision timer for an industrial corrosion monitoring device. On startup the GPS would report UTC plus one second. Within 12.5 minutes it would report exactly UTC, i.e. after reception of the GPS/UTC correction factor. I could only assume that the GPS developers had pre-programmed in the UTC/GPS clock offset that was current when the device was manufactured. Since then a UTC leap second had been added. Importantly, there is no way to tell which of those times the GPS is reporting. No doubt the precise behavior varies from chipset to chipset. For my project I was using a SiRF III receiver and could switch on the raw 50bps data steam and watch for the GPS/UTC correction to be sure when I had UTC time. AFAIK, there is no way of doing that on Android, so for truly accurate times your best bet is to leave the GPS on for 12.5 minutes before reading the time, and hope that it has successfully received the clock correction. -- Andrew -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
The Wikipedia article on GPS has a lot of info. The Official source of info would be: http://www.gps.gov/technical/ Lots of technical PDFs there! I used the Interface Control Document IS-GPS-200 and SPS Performance Standard Specification, mostly the latter. In short, though, the GPS comms cycle involves sending 25 pages of data at 50bps. Each page takes 30sec to be received and contains the complete ephemeris for the satellite and 1/25th of the almanac. 25*30sec = 12.5 minutes. One of the almanac pages contains the GPS/UTC correction. All satellites transmit the same almanac, which is good for several days. Each satellite transmits its own ephemeris, which is good for a few hours. Receivers will frequently store this info for faster startup. Devices with Internet capability (say, Android smartphones :-) can download everything from the Internet. I should mention that all satellites appear to transmit the almanac in sync. I never saw the GPS/UTC correction message any faster than every 12.5 minutes no matter how many satellites were visible. The problem for timing is that there is no way to tell what GPS/UTC offset is actually being applied by the receiver. I have not seen any comms protocol that includes this info, not NMEA, not SiRF. Android limits your options. There is simply no way to be *sure*. The best I could come up with was listening to the raw data, but you can't do that on Android. -- Andrew -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
I've not looked at the relevant Android API before, but I would imagine that if you get a GpsStatus object from the LocationManager, then check each satellite for hasAlmanac(), then you might be more likely to have the correct GPS/UTC offset. It is still possible to have received the almanac data for all satellites in view, but still not received the GPS/UTC offset, so not a perfect solution. -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
not an expert on that matter - good one. Keep it up. On Sunday, April 22, 2012 8:20:57 PM UTC-4, StarTraX wrote: Ibendin, I think it's good practice to employ words like perhaps, possibly or maybe when speculating on technical subjects. It's less confusing to the reader and makes it clear that one is not an expert on the matter. On Monday, April 23, 2012 9:42:50 AM UTC+10, lbendlin wrote: The OEM for your device decided to use UTC rather than GPS time. On Sunday, April 22, 2012 6:05:12 PM UTC-4, StarTraX wrote: I can assure you that the time reported by the quoted gpsclock site is NOT the time reported by GPS devices. It's really easy to demonstrate: Compare what you see on your GPS with what's displayed from the web site. The quoted time is around 15 seconds ahead of the time from the GPS device. I wonder what that's really all about? On Mon, Apr 23, 2012 at 5:08 AM, lbendlin l...@bendlin.us wrote: http://leapsecond.com/java/gpsclock.htm That explains the +/- some seconds. As I mentioned already, GPS chips on phones are cheap and cheerful. They use all kinds of dirty tricks to cut corners (AGPS etc). You probably won't find two smartphone models (even from the same OEM) that have the same GPS behavior . On Sunday, April 22, 2012 10:00:31 AM UTC-4, Panam wrote: Just to let you know, I am currently experimenting with GPS on a S Galaxy I whose GPS is off about 24 hs in the future (+-some seconds) and it does not seem to depend on the system time (adjusted the system time by some minutes without effects). This seems to be a systematic error. Btw. does somebody know an free app that shows the GPS time + date? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en On Monday, April 23, 2012 9:42:50 AM UTC+10, lbendlin wrote: The OEM for your device decided to use UTC rather than GPS time. On Sunday, April 22, 2012 6:05:12 PM UTC-4, StarTraX wrote: I can assure you that the time reported by the quoted gpsclock site is NOT the time reported by GPS devices. It's really easy to demonstrate: Compare what you see on your GPS with what's displayed from the web site. The quoted time is around 15 seconds ahead of the time from the GPS device. I wonder what that's really all about? On Mon, Apr 23, 2012 at 5:08 AM, lbendlin l...@bendlin.us wrote: http://leapsecond.com/java/gpsclock.htm That explains the +/- some seconds. As I mentioned already, GPS chips on phones are cheap and cheerful. They use all kinds of dirty tricks to cut corners (AGPS etc). You probably won't find two smartphone models (even from the same OEM) that have the same GPS behavior . On Sunday, April 22, 2012 10:00:31 AM UTC-4, Panam wrote: Just to let you know, I am currently experimenting with GPS on a S Galaxy I whose GPS is off about 24 hs in the future (+-some seconds) and it does not seem to depend on the system time (adjusted the system time by some minutes without effects). This seems to be a systematic error. Btw. does somebody know an free app that shows the GPS time + date? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
I could probably knock you up one quite quickly as I'm currently spending a
lot of time in that space. Could you be more specific about your
requirements? Maybe communicate directly with me through the info {at}
gpsanimator {dot} com
On Mon, Apr 23, 2012 at 12:00 AM, Panam pandem...@googlemail.com wrote:
Just to let you know, I am currently experimenting with GPS on a S Galaxy
I whose GPS is off about 24 hs in the future (+-some seconds) and it does
not seem to depend on the system time (adjusted the system time by some
minutes without effects). This seems to be a systematic error.
Btw. does somebody know an free app that shows the GPS time + date?
--
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Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
I can assure you that the time reported by the quoted gpsclock site is NOT the time reported by GPS devices. It's really easy to demonstrate: Compare what you see on your GPS with what's displayed from the web site. The quoted time is around 15 seconds ahead of the time from the GPS device. I wonder what that's really all about? On Mon, Apr 23, 2012 at 5:08 AM, lbendlin l...@bendlin.us wrote: http://leapsecond.com/java/gpsclock.htm That explains the +/- some seconds. As I mentioned already, GPS chips on phones are cheap and cheerful. They use all kinds of dirty tricks to cut corners (AGPS etc). You probably won't find two smartphone models (even from the same OEM) that have the same GPS behavior . On Sunday, April 22, 2012 10:00:31 AM UTC-4, Panam wrote: Just to let you know, I am currently experimenting with GPS on a S Galaxy I whose GPS is off about 24 hs in the future (+-some seconds) and it does not seem to depend on the system time (adjusted the system time by some minutes without effects). This seems to be a systematic error. Btw. does somebody know an free app that shows the GPS time + date? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
The OEM for your device decided to use UTC rather than GPS time. On Sunday, April 22, 2012 6:05:12 PM UTC-4, StarTraX wrote: I can assure you that the time reported by the quoted gpsclock site is NOT the time reported by GPS devices. It's really easy to demonstrate: Compare what you see on your GPS with what's displayed from the web site. The quoted time is around 15 seconds ahead of the time from the GPS device. I wonder what that's really all about? On Mon, Apr 23, 2012 at 5:08 AM, lbendlin l...@bendlin.us wrote: http://leapsecond.com/java/gpsclock.htm That explains the +/- some seconds. As I mentioned already, GPS chips on phones are cheap and cheerful. They use all kinds of dirty tricks to cut corners (AGPS etc). You probably won't find two smartphone models (even from the same OEM) that have the same GPS behavior . On Sunday, April 22, 2012 10:00:31 AM UTC-4, Panam wrote: Just to let you know, I am currently experimenting with GPS on a S Galaxy I whose GPS is off about 24 hs in the future (+-some seconds) and it does not seem to depend on the system time (adjusted the system time by some minutes without effects). This seems to be a systematic error. Btw. does somebody know an free app that shows the GPS time + date? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
Re: [android-developers] Re: How to get accurate time stamps from Android GPS location.
Ibendin, I think it's good practice to employ words like perhaps, possibly or maybe when speculating on technical subjects. It's less confusing to the reader and makes it clear that one is not an expert on the matter. On Monday, April 23, 2012 9:42:50 AM UTC+10, lbendlin wrote: The OEM for your device decided to use UTC rather than GPS time. On Sunday, April 22, 2012 6:05:12 PM UTC-4, StarTraX wrote: I can assure you that the time reported by the quoted gpsclock site is NOT the time reported by GPS devices. It's really easy to demonstrate: Compare what you see on your GPS with what's displayed from the web site. The quoted time is around 15 seconds ahead of the time from the GPS device. I wonder what that's really all about? On Mon, Apr 23, 2012 at 5:08 AM, lbendlin l...@bendlin.us wrote: http://leapsecond.com/java/gpsclock.htm That explains the +/- some seconds. As I mentioned already, GPS chips on phones are cheap and cheerful. They use all kinds of dirty tricks to cut corners (AGPS etc). You probably won't find two smartphone models (even from the same OEM) that have the same GPS behavior . On Sunday, April 22, 2012 10:00:31 AM UTC-4, Panam wrote: Just to let you know, I am currently experimenting with GPS on a S Galaxy I whose GPS is off about 24 hs in the future (+-some seconds) and it does not seem to depend on the system time (adjusted the system time by some minutes without effects). This seems to be a systematic error. Btw. does somebody know an free app that shows the GPS time + date? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en On Monday, April 23, 2012 9:42:50 AM UTC+10, lbendlin wrote: The OEM for your device decided to use UTC rather than GPS time. On Sunday, April 22, 2012 6:05:12 PM UTC-4, StarTraX wrote: I can assure you that the time reported by the quoted gpsclock site is NOT the time reported by GPS devices. It's really easy to demonstrate: Compare what you see on your GPS with what's displayed from the web site. The quoted time is around 15 seconds ahead of the time from the GPS device. I wonder what that's really all about? On Mon, Apr 23, 2012 at 5:08 AM, lbendlin l...@bendlin.us wrote: http://leapsecond.com/java/gpsclock.htm That explains the +/- some seconds. As I mentioned already, GPS chips on phones are cheap and cheerful. They use all kinds of dirty tricks to cut corners (AGPS etc). You probably won't find two smartphone models (even from the same OEM) that have the same GPS behavior . On Sunday, April 22, 2012 10:00:31 AM UTC-4, Panam wrote: Just to let you know, I am currently experimenting with GPS on a S Galaxy I whose GPS is off about 24 hs in the future (+-some seconds) and it does not seem to depend on the system time (adjusted the system time by some minutes without effects). This seems to be a systematic error. Btw. does somebody know an free app that shows the GPS time + date? -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -- You received this message because you are subscribed to the Google Groups Android Developers group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
