Tag Archives: GPS

Finding Waypoints

Here is the map of the locations of the waypoints to find. At each point there is a yellow label with the name of a person or place from forest history that is prominent in the¬†America’s First Forest documentary.

Overview of How GPS Works

Create a Map of Your Woodlot with a GPS and Google Earth

Click here to see the KML Tools Page.

GPS Testing

During the GPS testing lab each team recorded the UTM coordinates 25 times at each of five points.We finished with 200 measurements for each of the test points. We combined all the measurements for each of the points and calculated descriptive statistics.

The difference of each point from the average coordinate was calculated using the Pythagorean theorem. Histograms of the differences show a big difference in the results. In point 1 there was a great deal of difference among the results of each team. The combined data shows the wide variation. It would probably be a good idea to remeasure this point. Since the teams all used the same model of GPS receiver and measured during the same time period, these results point to a likely user error.

Point1histogram.jpgFor point 5 the differences are much smaller overall. They are also much more concentrated, indicating that all the readings were concentrated around the average, a consistent fix on the coordinates.

point5histogram.jpgNote that these charts used all the data points.

GPS Testing

During the GPS testing lab each team recorded the UTM coordinates 25 times at each of five points. After combining the readings I wanted to see if the results were statistically compatible or if they shouldn’t be compared. Another way to put it: are each team’s results form the same population or are there other factors that make the results not comparable.

There are some statistical methods to do this analysis. However, a simple way is to take the average of the eastings and northings, calculate the difference of each coordinate pair from the average, and plot the differences. The results should look like a scatter shot from shooting a target.

At point 5, the results seem to be randomly scattered around the average, or bullseye. The size of the spread is not very great.

Point 5 differences-corrected.jpg

Click on the thumbnail to see a larger version.

Point 1, on the other hand, shows the readings divided into distinct groups. Also, the magnitude of the differences is much greater.


All of the teams worked in the same time period, which means that GPS reception conditions must have been similar. The differences could be due to the differences between the GPS receiver units. More likely there was some variation in the operators or human error. I would recommend remeasuring this point to rule out human error.

Russian Rocket Fails with Three Satellites On Board

Yesterday a Russian rocket crashed near Hawaii with three satellites on board shortly after launch. The satellites were destined to be part of the GLONASS satellite navigation, which operates similarly to the American NAVSTAR GPS or the European Galileo.

Follow this link to a Yahoo News article quoting from an AFP article where Russian Prime Minister Putin stresses the importance of GLONASS to offset US influence. He wants all Russian cars to be equipped with GLONASS. In another article he said that he wanted cell phones sold in Russia to use GLONASS instead of NAVSTAR. He would also heavily tax units that use the American navigation system. See the Reuters article.

I was under the impression that the Russians wanted to sell their system to the world, which makes sense. I was surprised, but not that much, they would institute such a restrictive policy at home.

In this Russian article, the launch failure is attributed to a programming error, which reminds me of the mathematical units error that caused the loss of a NASA Mars explorer vessel. You have to check the programming!The article also has pictures of the launch.

The launch failure shouldn’t hurt the systems, which is already operational over all of Russia with 26 satellites in service.

Bear Trackers Use GPS in Bid to Preserve Animals


This article  on CNN describes how black bears in South Florida are being fitted with GPS collars to track their migration habits. The bears are facing an increasingly restricted environment which leads them to be isolated so that many of them are experiencing a loss of genetic diversity.

The researchers use doughnuts to entice the bears to traps. (They didn’t say which flavor.) The bears are then anaesthetized and fitted with tags and a collar. Hair samples are also taken for genetic testing.

The results of the work should show how much land needs to be conserved so that the bears have room to migrate and maintain healthy breeding populations.

The article doesn’t make clear that the GPS data has to be transmitted somehow from the collar so that it can be analyzed. In the captions of the photo galleries it says a text messaging system is used to relay the data. That’s an important link since a plain GPS receiver doesn’t transmit data.

Photo from the Flickr Digital Commons. American Black Bear. Lincoln Park Zoo mammal. 1900.

GPS Practice

Today we practiced saving waypoints and tracks with the Garmin 76 GPS. Here is a  map of our work.

View Larger Map

GPS Seclective Availability

During the introduction to GPS class yesterday we discussed the issue of Selective Availability (SA), which was discontinued in May, 2000. SA is the purposeful introduction of an error in the timing signal so that civilian users cannot get an accurate signal without using differential GPS. Specially equipped military GPS can remove the error on the fly.

The decision to turn off SA was made to promote GPS for civilian use. As more users came on board the degraded signal actually became a big obstacle. Also, the military developed other ways to limit the degradation of signal to battlefield areas. There is an interesting article in Wikipedia that describes SA and why it was eliminated.

The Wikipedia article notes that President Reagan directed that GPS be opened to civilian use as a public resource after the downing of the Korean Airlines 747 by the Soviets in 1983. I didn’t realize that was the reason this high security system was opened up.

Currently, although highly unlikely, SA could be turned back on by the Department of Defense. However, DOD announced in fall 2007 that the new GPS III generation of satellites would not have SA capability at all.

GPS is a great example of how military technologies eventually make their way to civilian use for the benefit of all. It would be great if that tremendous research and development capabilty could be musted without the need for wars.


File Format Questions

Everyone seemed to have the GPS data downloading working well. Several of you had questions about which program to use for the different tasks. Also, the file formats are important. As you work with digital geographic data you will find that file formats can really get confusing.

In USA Photomaps everything is included in the program. It is really not meant to share data with other applications. If you look in the program folder you will see that data is stored in xml format files. Xml  is a data base specification for text files. Many programs use it in one form or another. One more USA Photomaps hint. It’s best to create a new file (Map Location) for each area you work in. It makes it easier to store the waypoints and tracks separately. Also, when you open the file it will got directly to the area you are interested in.

DNR Garmin is a utility program. It doesn’t really do much by itself. It prepares the data for use by another program. Most of the time we convert the data to ArcView shape files (another format). In our case we are converting the data to kml format. Kml is a special text file that Google Earth and Google Maps can read.