I’ve been using a GPS Micro-Mini in SiRF binary mode. Sitting in one place and testing the GPS, I recieve XYZ locational data that have awful accuracy. Calculating the distance between measurement gives me a accuracy <50m and the chip is suppose to be accurate <3m. So I’m confused. :?
Is something wrong with the chip?
I’m fairly confident that I’m reading in the values correctly on my MSP430 UART so that shouldn’t be the problem.
I’ve also read in NMEA data but I’m not sure how to calculate distance from longitude and lattitude. However the accuracy doesn’t seem right either.
Thanks in advance for any help.
GPS accuracy will vary wildly depending on current conditions. Get the unit outside with a nice clear view of most of the sky. Let it sit there running for 30 min or so, then check it. It has to download a bunch of data from a really slow datastream from the satellites. It takes a while to get it the first time. After that, locks should be faster and more accurate.
Short version: Don’t ever expect GPS to be <3M accuracy at any given moment. It might be, but you can’t guarantee that. Just because the chip can do it, sometimes, under ideal conditions, that doesn’t mean it will often.
Thanks,
I was testing it outside for about an with clear view of sky.
So from what you said, I can’t expect great accuracy from the GPS even most of the time.
I had originally wanted to set gps points that I can then detect when I arrive at those points but it seems that this would be a lot more difficult than I thought with this accuracy issue. Any suggestions on how I should proceed?
You can set up your software to be a little easier on the matching. There are other things that can help, but GPS just isn’t all that accurate. It’s pretty darn good for a bunch of satellites, but it’s not going to give you cm accuracy at these sorts of prices. 
Others might be more help depending on your application. What are you trying to do? The UAV sensor platform might be useful.