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Topic: Problems with sim908 and coordinates (Read 1 time) previous topic - next topic

xload

Hello, I'm working with sim908, usually it works well and give me the correct location, but sometimes it returns bad locations, they are too far from real location, to obtain the location I check if SIM908 is 3D fixed with AT+CGPSSTATUS? command, and then I get the location with AT+CGPSINF=0 command.

Here you can see an example with converted coordinates:
real position: 41.680399466667 -0.8860718
sim908 position: 41.675466983333 -0.8852484

┬┐somebody can help me?

pylon

The coordinates look like you're inside a building and the GPS reading is about 300m off your real position. That's an acceptable offset for your situation in my opinion given that you're using a GPS module with only a small integrated antenna. Go to an outdoor place where you have at least a 90┬░ clear sky (no obstacles like trees or buildings) and measure again. You'll probably get readings that are accurate to about 5-10m.

xload


The coordinates look like you're inside a building and the GPS reading is about 300m off your real position. That's an acceptable offset for your situation in my opinion given that you're using a GPS module with only a small integrated antenna. Go to an outdoor place where you have at least a 90┬░ clear sky (no obstacles like trees or buildings) and measure again. You'll probably get readings that are accurate to about 5-10m.


Hello pylon, we are testing outdoor with hardware inside a plastic box, we use this antenna http://www.cooking-hacks.com/internal-gps-antenna, most positions are on 10m radius from real position, but some positiong give the wrong position, we take 72 position and only 2 are bad.

pylon

Quote
Hello pylon, we are testing outdoor with hardware inside a plastic box, we use this antenna http://www.cooking-hacks.com/internal-gps-antenna, most positions are on 10m radius from real position, but some positiong give the wrong position, we take 72 position and only 2 are bad.


You may be outdoors but inside a town and I guess that you have high buildings around you. Depending on the current satellite positions there may be smaller or bigger errors because of that (absorptions and reflections). Did you try under an open sky?

I don't know your specific GPS hardware but I have quite some experience with other GPS hardware under varying circumstances and if that hardware is not installed on a ocean ship or something similar, never trust a single measurement, always take several and build some meaningful average from them.

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