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2016-01-06 09:35:29 -0600 commented answer 4wheel skid-steer - weird behaviour

I am looking at this again and can reproduce similar (but different) weird behaviours by starting with the standard Pioneer 3AT model from the gazebo library. The basic version of it works fine. But I get the behaviours if I place the front and back axles further apart, eg. 0.5m apart. I wonder, is this some fundamental property of skid steers , or perhaps it needs the friction param to be updated for each new configuratin? Can anyone suggest friction params for 1m spacing?

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2015-11-19 08:25:09 -0600 asked a question 4wheel skid-steer - weird behaviour

I've set up a 4-wheeled skid-steer (differential drive) sim and am testing turn-on-the-spot. With a plugin I set both right wheels to go forward, velocity 1, and the left ones backwards, velocity 1.

Result is that for 90 degrees, the robot turns on the spot as expected. But the it goes in a straight line for a couple of meters, then turns another 90 degrees, and so on to make a kind of rounded-corners square path.

I've tried playing with surface friction params but not seemign to make much difference. Is this is known issue with 4wheel skid steer sims or could something else be wrong?

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2015-11-06 09:57:06 -0600 answered a question heightmap "Coordinates out of range" error

Answering own question for future reference -- problem was that pngs were still being saved as 16bit not 8bit. Looks like Gazebo interprets 16bit image values as pairs of 8bit values, which gives rise to the choppy/buggy appearance.

2015-11-06 09:32:03 -0600 asked a question Heightmap -- how to get sub-meter accuracy?

I'm working with some DEM data containing hills and mountains, and want to simulate a robot driving over them. The difference in heights at the top and base is more than 250m and I have DEM data to ~10cm accuracy. How can I get this into gazebo?

I first tried using png terrains with heightmap. With an 8bit png I can only represent color depth with ints from 0-255, which only gives 1m accuracy. 16bit pngs make gazebo fail, it interprets the 2-byte codes as two separate points.

I'm now trying DEM format files but having trouble understanding how to write to the DEM format (I need to generate the terrain programatically). Wikipedia's DEM page is not so helpful and there doesn't seem to be much else around.

Any suggestions how to do this?

2015-11-06 09:16:57 -0600 asked a question heightmap "Coordinates out of range" error

Hi,

I'm looking at the heightmap tools in gazebo but getting this error. The heightmap works OK when I use the shipped example png:

<collision name="collision"> <geometry> <heightmap> <uri>file://media/materials/textures/heightmap_bowl.png</uri> <size>1 1 1</size> <pos>0 0 0</pos> </heightmap> </geometry> </collision>

But when I swich to my own png I get a load of errors like Error [Image.cc:311] Image: Coordinates out of range [995 1024]

Something gets loaded into gazebo, I can see a spiky terrain (it should be smooth) that suggests there may be some problem interpreting bytes as pixels. There is an area that's all zero height which does display correctly.

My own png has 1025x1025 pixels, and I've tried saving it in 8-bit (heights 0-255) and 16-bit, with no change to the error. It is supposed to represent an area of 2050m x 2050m, with heights from 0 to 250m.

Is there something I need to change in the size setting perhaps, I have tried <size>2050 2050 250</size> but still getting the error.