# GPS tracking – trip to the Cities

January 9, 2011 2 Comments

To further test my Phi-1 shield‘s capability to track and store GPS information, I used the GPS logger program that I wrote during a trip to the Cities. Here is a map that I made with gps visualizer:

If I zoom into the details, I can see the coordinates match relatively well with google map, except for places that I highlighted in the inset on the bottom right. The big bend that I drove through, with an inset on the top right, seems ok but not for the other big bend. Plus, the logger recorded about 600 points, with the first few as zeros. I will have to find out why it’s recording zeros. Plus, there is one time the same coordinates were recorded 4 times. Have to find out what’s causing this, the TinyGPS library or my code. I also tried to calculate the speed and compare with the GPS speed. The results are not very accurate, sometime off by 30%.

Here is what I used as an estimate: SQRT((Lat change)^2+ (Long change)^2)/(time change)*1.11

The 1.11 accounts for the factor between 10 micro degrees and 1 meter. From the radius of the earth, 6370Km, and the 360 degrees of latitudes or longitude. I think I have made a mistake on the latitude. Will derive an accurate formula later though. But overall I’m alright with my GPS logger. I will hopefully have more time to add more display functions to it so I can read all information from the GPS, including speed, time, altitude, etc. while it records. Right now it only displays Lat/Long as it records.

You forgot that although one degree of

latitudemay be about 110km, and one degree of longitudeat the equatoris also about 110km, Minneapolis is at 45 degrees north, not at the equator, so each degree of longitude is only about 79km.(and of course if you travel a significant distance north or south, the factor changes — but as long as you stay within 100km or so of where you started, the approximation should be good within a percent or two)