[Gta04-owner] Advance OpenStreetMap surveying with GTA04? / camera & heading

Christoph Mair christoph.mair at gmail.com
Mon Mar 19 22:29:46 CET 2012


Hi,

On Mon, Mar 19, 2012 at 1:44 PM,  <mayeul.kauffmann at free.fr> wrote:
> Hi,
> Thanks Christoph. Comments below:
>> There exists a simple hack that reads the raw
>> acceleration values from the chip and delivers them to userspace using
>> a sysfs file
>
> I've read [0] but could not find it description of this hack. Any pointer and sample strings?

I attached a patch to get some values from the BMA180 accelerometer.
It should apply to the 3.2-gta04 tree. I have not tested it lately, so
it may just fail. When my flat battery is recharged I can test it too.

> The LSM303DLH combines both 3D compass and accelerometer, so is the HMC5883L usefull for this application?

We planned to use the LSM303DLH but we could not buy it in time.
Therefore we had to find a replacement. The BMA180 and the HMC5883l
have better specs than the LSM303 so the replacement should bring us a
slight improvement in accuracy.

> So one idea is to put some tilt logic in the code here:
> http://gitorious.org/vala-compass/vala-compass/trees/master/src
> Or write a piece of code that takes the raw data and output tilt-corrected magnetic heading.
> I found out some math and code (for Arduino) that could be re-used. Most interesting are [3] to [5]:
>
>
> [1] Has nice geometric discussion and code, but cannot correct for tilt over 40 degrees. Saysthere are other (more complex) algorithms for tilt > 40°.
> [2] Give some pointers to scientific articles, including I believe for 360 degrees correction.
> Note that typical use is keeping the device vertical, so code in [1] is not OK
> [3] Discusses the LSM303DLH chip included in the GTA04, and gives 2 links for code computing the tilt-corrected heading:
> [4] Arduino code for LSM303DLH
> [5] In "Ressources" tab: "library for the ARM mbed development board that interfaces with the LSM303DLH 3D compass and accelerometer carrier and provides the tilt-compensated magnetic heading"
>
> Isn't [5] the closest to what would be needed? Could it serve as a basis?

This sound very promising. I still have to read all these links
(hopefully tomorrow) but the last one is probably what you need.

Christoph


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