Re: [talk-au] GPS accuracy
On 22/09/12 10:20, Ben Johnson wrote: That is absolutely fantastic - cant wait to see it. BJ It should be available now if you tell JOSM to download a new plugin list. It's called GPSBlam. http://wiki.openstreetmap.org/wiki/JOSM/Plugins/GPSBlam Please tell me it works as it was a bit of a black art getting it up into the repository! Cheers Russell ___ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au
Re: [talk-au] GPS accuracy
Hi Russell, I've installed and run it in JOSM OK. But I see it operates only for straight lines. I was hoping it'd average GPS traces downloaded from OSM in JOSM around corners and curves. That would be a big ask, I know. John On 24/09/12 01:16, Russell Edwards wrote: On 22/09/12 10:20, Ben Johnson wrote: That is absolutely fantastic - cant wait to see it. BJ It should be available now if you tell JOSM to download a new plugin list. It's called GPSBlam. http://wiki.openstreetmap.org/wiki/JOSM/Plugins/GPSBlam Please tell me it works as it was a bit of a black art getting it up into the repository! Cheers Russell ___ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au ___ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au
Re: [talk-au] GPS accuracy
On the topic of accuracy, some GPS's also have gyroscopes and accelerometers and compasses to error correct the GPS data. They're getting complicated enough now I don't like to comment on when/where they work well. There's just too many variables the algorithms are tweaked constantly by software updates. On 21/09/2012, at 9:38, Brett Russell brussell...@live.com.au wrote: My goal is pratical accuracy. By that, avoiding my GPS complaining with OSM that I am heading into oncomming traffic. The issue with that was the particular road was aligned to native Bing so was say five to ten metres out. If I can establish the correct alignment of Bing for the area then I can have the road in the correct place. Now of course if my GPS can not resolve to the necessary accuracy then I still will have the issue but that is between my GPS and OSM rather than OSM and the real position. I find the only way to get an accurate road position, especially corners/intersections or in poor signal areas, is to make several traces. But honestly I don't worry about it too much. A road that is 10 or even 50 meters off is better than no road at all on the map (especially in remote areas where most of the missing roads are). If I've only got a single poor quality trace I'll still put it in. Somebody else (or maybe me) will notice eventually and take the time to replace it with more accurate data. When reading the map, a GPS needs to allow for inaccuracies in it's own signal anyway, so in practice they handle it well. Of course, make it as good as you can, and fix other people's inaccurate data when you notice it, but I'm just saying if you have a bad trace and don't plan to drive down the road again 5 more times, by all means put what you've got on the map. When I know my trace is bad, I like to enter it with big gaps between each point, so you see straight lines and hard corners instead of a nicely flowing road on the map. Gradually working my way around Tassie by lake tracing and that is where I am understanding the challenges Bing gives you. Its image quality ranges from top class to murky but still great to have it as the alternative would be walking around every lake, tarn and pool. Sometimes I load my traces into google earth, since that has much higher quality satellite photos, to get an idea how far off my trace is. - Abhi ___ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au
Re: [talk-au] GPS accuracy
On 24/09/12 06:21, Abhi Beckert wrote: Somebody else (or maybe me) will notice eventually and take the time to replace it with more accurate data. Or, having taken great pains to get it very accurate, somebody will correct it with wildly inaccurate data. Sometimes from imagery with a big offset (incorrect datum). But that's life. John ___ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au
Re: [talk-au] GPS accuracy
Hi Russell, Congratulations mate. It works - I tested it under both Mac OS/X (Leopard 10.5.8), and Linux (Ubuntu 12.04.1). I reckon this will now be my favorite method to line-up background images! Only a minor thing - (on the Mac at least) your scroll wheel method didn't work for me, but I prefer to use the arrows anyway because (for me) it's a bit tricky to click/drag then use scroll wheel while still holding onto the mouse button - that's a minor thing and it might just be me. I can try the wheel again if it's important for you to know for sure... Didn't try the scroll wheel method under Ubuntu as I use the trackpad on that machine but I can connect a mouse if you want it tested. Cheers, BJ On 24/09/2012, at 1:16 AM, Russell Edwards wrote: On 22/09/12 10:20, Ben Johnson wrote: That is absolutely fantastic - cant wait to see it. BJ It should be available now if you tell JOSM to download a new plugin list. It's called GPSBlam. http://wiki.openstreetmap.org/wiki/JOSM/Plugins/GPSBlam Please tell me it works as it was a bit of a black art getting it up into the repository! Cheers Russell ___ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au
Re: [talk-au] GPS accuracy
That is absolutely fantastic - cant wait to see it. BJ Sent from my iPhone On 21/09/2012, at 12:20, Russell Edwards russ...@edwds.net wrote: Hi all, On this topic -- for what it's worth I have written a JOSM plugin to help with GPS accuracy in the case of having multiple tracks covering the same . You can highlight a set of GPX tracks along a straight path (or taken from a fixed position) and it will a) average them all to find their geometric centre and b) find the direction of maximum variation, to find the likely direction of the path along which they were recorded. I hope to have it available within the next week or two. You should get an accuracy improvement factor of equal to or greater than the square root of the number of tracks. When you have dozens or hundreds of tracks on the same paths, as I do (logs from my runs around town), then it should be a great help in pinning down any offset in the imagery (and potentially, rotation, too). Russell ___ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au ___ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au
[talk-au] GPS accuracy
On 20/09/2012 3:49 PM, Brett Russell signalled: Been reading up on GPS accuracy and playing with averaging waypoints on the Garmin 62S and have realised that WAAS does not work outside the USA and for some units better to have it switched off. If I wrong in my understanding please let me know. I can be rather a precision freak but be nice to get thing right. Discovering the accuracy of a unit is easy. Find a convenient spot near your house and with your GPS record its position. Come back next day (or at least a few hours later) and do it again. Repeat daily until you are sick of it and you will then have a good idea of how accurate any particular observation is likely to be. No technical expertise required. The question of absolute accuracy is complex. Survey marks mostly were placed before the current modelling of the earth was developed. While these may now have GDA coordinates (typically about 100 mm different from WGS in Australia) there are complexities that arise (eg from continental drift and the instability of the earth's axis of rotation) which are significant variables. There are many assumptions in the modelling. WAAS also works in Europe and Japan. There is no likelihood of it being implemented in Australia as our population density is too low. Switch it off. If it is left switched on there is some risk that spurious signals from other systems may degrade the accuracy of your device. Regards, Peter -- There are no problems more difficult to overcome than those which are merely imagined. We never approach the truth in what we say unless that includes the expectation of being wrong ___ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au
Re: [talk-au] GPS accuracy
On 20/09/12 22:27, Peter Hoban wrote: Discovering the accuracy of a unit is easy. Find a convenient spot near your house and with your GPS record its position. Come back next day (or at least a few hours later) and do it again. Repeat daily until you are sick of it and you will then have a good idea of how accurate any particular observation is likely to be. No technical expertise required. The question of absolute accuracy is complex. Survey marks mostly were placed before the current modelling of the earth was developed. While these may now have GDA coordinates (typically about 100 mm different from WGS in Australia) there are complexities that arise (eg from continental drift and the instability of the earth's axis of rotation) which are significant variables. There are many assumptions in the modelling. WAAS also works in Europe and Japan. There is no likelihood of it being implemented in Australia as our population density is too low. Switch it off. If it is left switched on there is some risk that spurious signals from other systems may degrade the accuracy of your device. I've been using a Garmin GPSMAP 60CSx for a number of years. Normally for logging GPS tracks by car for use in OSM, I use it in conjunction with an external antenna (mounted above the driver's seat so it's closer to the centre of the road). With a good view of the sky, this GPS unit usually claims its accuracy to be ± 3m, with one important exception. And that's when cornering. If I superimpose track logs from several days in JOSM, I do see incredible consistency in the tracks. The exception is in the corners, where there's distinct variation. The solution is to drive around corners more slowly (where safety considerations permit). Then the GPS seems more inclined to accept cornering as the reason for the deviation from going straight ahead (rather than its interpreting the change in direction as resulting from a noisy or degraded satellite signal instead). I've struck another situation where the GPS reports significant uncertainty about its position. That's when bushwalking with thick tree cover and especially with cliffs or hills to one or both sides. It's clear to me that the signal is weak, with echoes only making the situation worse. Here the GPS might report an accuracy in the order of ±15m, and superimposed logs confirm this variation. John ___ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au
Re: [talk-au] GPS accuracy
Hi all Interesting discussion and thanks for confirming that WAAS is not an option in Australia so I will switch it off. Subtle details like this get missed in various reviews and also means that USA and now likely European reviews with claims of accruacy need have factored in that WAAS might be enhancing accuracy that will not happen in Australia. Also now better placed to identify inexpert expert sales people. Point taken on absolute accurary considerations with survey marker location. My goal is pratical accuracy. By that, avoiding my GPS complaining with OSM that I am heading into oncomming traffic. The issue with that was the particular road was aligned to native Bing so was say five to ten metres out. If I can establish the correct alignment of Bing for the area then I can have the road in the correct place. Now of course if my GPS can not resolve to the necessary accuracy then I still will have the issue but that is between my GPS and OSM rather than OSM and the real position. I have found my Garmin 62s is remarkably consistent with traces as I have walked the same tracks now a few times and generally it is within 5 metres at least and more often than not within two metres. In the car it is readly aparent what side I am on with and out and back trips, until I reach a cutting, in that case the traces very rarely cross but do tend to broaden out. Courners do catch it out but then I have my recoding interval set to 10 metres as I am told that gives the best result for my unit. Now using aligned Bing to clean up and remove unnecessary points for roads but leaving more points in for finer detail for walking tracks as five metres off track can me rather painful scrub bash. My reading of various information suggests that the Garmin maps themselves, due to using 24 bit reference number, have at best a theortical accuracy of 2.5 metres so even with professional grade surveying the maps in the unit will not be better than 2.5 metres. Someone might have different or better information so more than happy to have this point challenged. All still very much a learning curve for me. Actually GPS accuracy needs to be remarkable with complicated intersections as often one lane out can mean a massive side trip. Spent a lot of time figuring out how to get to Ballarat from the Melboure Airport as for a Tasmanian we are not use to such massive intersections. I case where I should have been the navigator not the driver. Was pre OSM for me so was usuing Google Maps on the iPhone. Gradually working my way around Tassie by lake tracing and that is where I am understanding the challenges Bing gives you. Its image quality ranges from top class to murky but still great to have it as the alternative would be walking around every lake, tarn and pool. Anyway thanks for the feedback. Hopefullty it will result in better maps. Cheers Brett Date: Fri, 21 Sep 2012 06:23:13 +1000 From: snow...@gmx.com To: talk-au@openstreetmap.org Subject: Re: [talk-au] GPS accuracy On 20/09/12 22:27, Peter Hoban wrote: Discovering the accuracy of a unit is easy. Find a convenient spot near your house and with your GPS record its position. Come back next day (or at least a few hours later) and do it again. Repeat daily until you are sick of it and you will then have a good idea of how accurate any particular observation is likely to be. No technical expertise required. The question of absolute accuracy is complex. Survey marks mostly were placed before the current modelling of the earth was developed. While these may now have GDA coordinates (typically about 100 mm different from WGS in Australia) there are complexities that arise (eg from continental drift and the instability of the earth's axis of rotation) which are significant variables. There are many assumptions in the modelling. WAAS also works in Europe and Japan. There is no likelihood of it being implemented in Australia as our population density is too low. Switch it off. If it is left switched on there is some risk that spurious signals from other systems may degrade the accuracy of your device. I've been using a Garmin GPSMAP 60CSx for a number of years. Normally for logging GPS tracks by car for use in OSM, I use it in conjunction with an external antenna (mounted above the driver's seat so it's closer to the centre of the road). With a good view of the sky, this GPS unit usually claims its accuracy to be ± 3m, with one important exception. And that's when cornering. If I superimpose track logs from several days in JOSM, I do see incredible consistency in the tracks. The exception is in the corners, where there's distinct variation. The solution is to drive around corners more slowly (where safety considerations permit). Then the GPS seems more inclined to accept cornering as the reason for the deviation from going straight ahead (rather than
Re: [talk-au] GPS accuracy
Hi all, On this topic -- for what it's worth I have written a JOSM plugin to help with GPS accuracy in the case of having multiple tracks covering the same . You can highlight a set of GPX tracks along a straight path (or taken from a fixed position) and it will a) average them all to find their geometric centre and b) find the direction of maximum variation, to find the likely direction of the path along which they were recorded. I hope to have it available within the next week or two. You should get an accuracy improvement factor of equal to or greater than the square root of the number of tracks. When you have dozens or hundreds of tracks on the same paths, as I do (logs from my runs around town), then it should be a great help in pinning down any offset in the imagery (and potentially, rotation, too). Russell ___ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au
