This page started on 05/25/04 and last updated 01/01/05

Previous | Index | Next

The Earth Explorer Project

GPS Experiments - 5/25/04

I connected my DeLorme TripMate GPS receiver to my laptop computer and walked around the farm. I stayed in the open areas, which aren't all that open anymore. The farm is approximately 1/4 mile on each side.

The image above shows the results. The green line shows the path that I walked. The red line is what the GPS receiver recorded. The path is way off. So I deciced to put the GPS in my car and drive around the road.

The image above shows the results. You can see that I back out of the driveway, drove around the circle and down the driveway. I drove north and turned at the corner to go down the dead end road. You can see I turned around in a driveway on the north side. I then drove back east and turn north at the corner. I went north about a mile and turned around. (That isn't visible since it is cut off at the top of the image.) I came back south and turned on the dead end road again. I followed the road to the end and turned around in a driveway on the south side. I drove back around by the house and continued south. When I got to the property line I did an S curve so I could indentify it later. I continued south and turned around. (That isn't visible since it is cut off at the bottom of the image.) I came back north and did the S curve at the property line again. I went back to the driveway and parked.

This all looks exactly right... I purposely put the GPS receiver in front of me on the dashboard so it would be in the center of the road as I drove. And you can see the recorded path retraces itself as I drive back and forth on the road.

So maybe it was that the 12/120V invertor or my laptop was causing interference when I was carring it around. So I connected a MiniRoboMind board to the GPS and walked around to test that. (It was also about 20 lbs lighter since I now didn't have a 15 Ahr battery and an invertor.) I also concluded the GPS receiver may need a ground plane to work correctly. So I placed the GPS receiver on a cookie sheet for this test.

The image above shows the results. They are way off again. Again the green line is the path that I walked. The red line is the recorded path.

So I will have to play with it some more...

More GPS Experiments - 12/24/04

I bought a new GPS receiver on eBay. It is a Rikaline GPS-6010 and it has a USB interface. I wanted to compare the new GPS receiver to my old Delorme Tripmate that I had problems with. I taped both receivers to a board and plugged them both into my new laptop. (I have a new laptop with new batteries. So I didn't have to carry a battery and invertor this time. :-) I wrote a Visual Basic program to read both receivers and write to separate files. I saved everything that was output so I can go back and check the satellite conditions along with the coordinates. I didn't do any extensive testing since it was getting cold and dark. I just wanted an approximate path that I could verify to see if I was getting better results. Below are aerial photographs with the data points.

Result from the Delorme Tripmate.

Result from the Rikaline.

Both plots superimposed.

It is obvious from these plots that the Rikaline receiver is working much better. The Tripmate seemed to work a little better this time also.

I didn't add the green path to show where I walked. Mainly because I'm not sure exactly where I went, since I was in a hurry. But the blue plot looks darn close. You can see it follows the road and property lines very well. It even retraces itselfs at the driveway which is the starting and ending point.

I haven't tried to verify the accuracy resolution. But the Rikaline has the new WAAS. (Wide Area Augmentation System) So I need to design some tests for that. The new receiver probably still won't keep a robot lawn mower out of a flower bed, but it looks like it will work great for mapping where my Earth Explorer has been.

I still haven't figured out why the Tripmate isn't working very well...

Previous | Index | Next

Visit Twin Cities Robotics Group
Back to my Home Page

This page is currently maintained by Jeff Sampson