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Georeferencing map coordinates

asked 2017-07-31 01:07:27 -0600

9a3eedi gravatar image

I was wondering how ROS handles georeferencing of map coordinates. My robot currently sets its position when it starts up as position 0.0. However this doesn't give any information about where I am in on earth.

How do I convert map coordinates to GPS coordinates and back again? That is, how do typical ROS-powered robots do it? TF doesn't seem suitable for this because converting GPS to map coordinates isn't as simple as a matrix transformation, if I understand correctly.

I'm also trying to figure out how to do this with map_server. As I understand, the map_server is initialized with a yaml file containing map coordinates of the underlying map. However, my robot could start up at any point on earth, so the yaml file would always be incorrect, if I set it to a particular map coordinate. How can I set up the map_server based on a GPS coordinate, rather than a map coordinate?

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answered 2017-07-31 01:23:06 -0600

tfoote gravatar image

It is true if you do large scale navigation that the euclidian assumptions of most maps does not hold. however if you use multiple maps they can make a pretty good approximation (That's basically how UTM coordinates work)

REP 105 describes how coordinate frames between map and earth frames is recommended to work.

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Can you define what "large scale" vs "small scale" means? Is 600 kilometers considered large scale? or 6,000 kilometers?

9a3eedi gravatar image 9a3eedi  ( 2017-08-01 01:09:51 -0600 )edit

I didn't specify as it's entirely dependent on your application and how precisely you need to know position. If you have higher tolerance you can allow larger approximations by using larger tangent planes.

tfoote gravatar image tfoote  ( 2017-08-01 14:34:36 -0600 )edit

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Asked: 2017-07-31 01:07:27 -0600

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Last updated: Jul 31 '17