Re: Open Source AHRS project: giving away hardware
On 05/11/2014 07:08 AM, joerg Reisenweber wrote: On Sat 10 May 2014 11:57:30 Pascal Gosselin wrote: calibrate the compass via GPS track by an easy calibration or self-calibration method GPS doesn't offer any data to calibrate magnetometer from. magnetometer aka compass is about orientation of device, GPS is about position and movement vector. They are 100% unrelated. In a static situation this is correct, but while moving it is possible to get the current heading from GPS. Jake ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: Open Source AHRS project: giving away hardware
Indeed. When you taxi an airplane on the ground in a straight live or drive a car in a straight line, GPS TRACK (adjusted for magnetic declination) = Magnetic Heading. The other complementary magnetometer calibration techniques involve driving around in a full circle in about 60 to 75 seconds or doing a 360 degree turn and stopping every 30 degrees. -Pascal Sent from my iPhone On May 11, 2014, at 4:47 AM, Jake jak...@rommel.stw.uni-erlangen.de wrote: On 05/11/2014 07:08 AM, joerg Reisenweber wrote: On Sat 10 May 2014 11:57:30 Pascal Gosselin wrote: calibrate the compass via GPS track by an easy calibration or self-calibration method GPS doesn't offer any data to calibrate magnetometer from. magnetometer aka compass is about orientation of device, GPS is about position and movement vector. They are 100% unrelated. In a static situation this is correct, but while moving it is possible to get the current heading from GPS. Jake ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: Open Source AHRS project: giving away hardware
On May 11, 2014, at 12:03 AM, Ben Wong lists.openmoko@wongs.net wrote: Sounds like a fun challenge. I'd take it up if I wasn't already so busy. After all, who in their life hasn't at one point wanted to write an Unscented Kalman Filter? ;-) Just out of curiosity, is OpenPilot.org not a viable solution? My understanding is that the code written for micro-controller platforms will need significant changes to work in a Linux environment. Of course re-using as much of the code as possible that is used for controlling most small drones totally makes sense. -Pascal ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: Open Source AHRS project: giving away hardware
On Sun 11 May 2014 09:25:37 Pascal Gosselin wrote: Indeed. When you taxi an airplane on the ground in a straight live or drive a car in a straight line, GPS TRACK (adjusted for magnetic declination) = Magnetic Heading. The other complementary magnetometer calibration techniques involve driving around in a full circle in about 60 to 75 seconds or doing a 360 degree turn and stopping every 30 degrees. -Pascal Sent from my iPhone On May 11, 2014, at 4:47 AM, Jake jak...@rommel.stw.uni-erlangen.de wrote: On 05/11/2014 07:08 AM, joerg Reisenweber wrote: On Sat 10 May 2014 11:57:30 Pascal Gosselin wrote: calibrate the compass via GPS track by an easy calibration or self-calibration method GPS doesn't offer any data to calibrate magnetometer from. magnetometer aka compass is about orientation of device, GPS is about position and movement vector. They are 100% unrelated. In a static situation this is correct, but while moving it is possible to get the current heading from GPS. Jake This all assumes a locked and defined mounting situation for the magnetometer. Then yes. For an embedded device however this method tells you nothing about the magnetometer heading. The embedded device can change relative orientation to the vehicle that's driving. PS: you must be very sure about the vehicle moving exactly straight ahead as well, for anything but a non-sliding car that's not guaranteed, think boat, even airplane -- () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments (alas the above page got scrapped due to resignation(!!), so here some supplementary links:) http://www.georgedillon.com/web/html_email_is_evil.shtml http://www.nonhtmlmail.org/campaign.html http://www.georgedillon.com/web/html_email_is_evil_still.shtml http://www.gerstbach.at/2004/ascii/ (German) signature.asc Description: This is a digitally signed message part. ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: Open Source AHRS project: giving away hardware
On 2014-05-11, 11:28 AM, joerg Reisenweber wrote: This all assumes a locked and defined mounting situation for the magnetometer. Then yes. For an embedded device however this method tells you nothing about the magnetometer heading. The embedded device can change relative orientation to the vehicle that's driving. PS: you must be very sure about the vehicle moving exactly straight ahead as well, for anything but a non-sliding car that's not guaranteed, think boat, even airplane We're talking calibration here. Yes the unit should be rigidly mounted for calibration of the sensors. There are also periods of stay still for X seconds at various points in such a calibration. I have done and continue to do lots and lots of AHRS calibrations of various types on aircraft (airplanes and helicopters). I would be more than happy to share the information that I have on various calibration techniques. Once the sensors are calibrated (i.e. figuring out the drift of the Rate Gyros when sitting still) and the magnetic environment of the device is known, what's left is the alignment procedure. Every time you start the AHRS code on the device, it would need to be motionless for a while. Lying the GTA02/GTA04 flat on a table for example for perhaps 2-3 minutes might be sufficient. I feel that this likely the reason why even the latest mainstream phones don't have AHRS or IMU capability (an IMU would enable indoor navigation over only very short distances in a smartphone, given the rather crude quality of the MEMS sensors and horrific gyro drift expected if you are bouncing around with the smartphone in your hand and moving rather slowly without GPS aiding the Kalman filter). Application for an AHRS on a smartphone would be for enhanced geo-referencing of photos and Google Glass type applications that don't make you look like a Glasshole. The other obvious application is as an emergency backup attitude (Pitch and Roll) and Heading indicator for airplanes and helicopters or simply recording of the sensor data and doing post-processing on a server to process the data later (think extreme sports, like playing back a skydive for example). -Pascal ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
