Geog 417 - Advanced GIS

Lab 2 - GPS 2

The task: calculate the accuracy of the handheld GPS receivers.

Step one - select a campus campus survey point. To find out where the points are and their surveyed locations, open the files in the GPS subdirectory (the monument file). If you examine the table associated with the points, you will see that the coordinates are recorded in both State Plane and UTM. I'll let you figure out which set is UTM.

Remember, the first thing you will do is clear the GPS's memory.

Now, head out to that point, stand over it, and log data - one point every 15 seconds or so for at least 15 minutes (bring a coffee or something). Collect the data in UTM Zone 10, NAD83 datum. TURN OFF BOTH GLONASS and WAAS (it's under setup - system). Make sure you spend the full 15 minutes, otherwise you won't get much variation in your points and the lab will be pretty pointless.

Next, do the same with EITHER GLONASS or WAAS enabled. About 15 minutes. Either save it as a new waypoints file or note the waypoint number when you started this. Note which is turned on.

Wander back into the lab, goto the back computer, download the data into a shapefile. Now, thanks to a new version of ArcGIS, one more step. You need to add the UTM coordinates as fields in the shapefile table. To do this, open ArcToolbox - data management tools - features - add geometry attributes. Select your shapefile, then check point_x_y_z_m. Scroll down and select UTM, NAD 83 as your coordinate system. We're in zone 10N. Run it. Now, if you look at the table, you will see UTM coordinates in there....

OK. Now take the .dbf file (one of the shapefile files) and MAKE A COPY - open this copy in Excel. Be sure to use the copy so you don't screw up the original.

Now for some stats (in excel)- do this seperately for each dataset (with and without glonass/waas). And answer the same questions for each dataset (questions 1-4).

  1. Calculate the average position in x,y, and z - also,calculate the average error in x,y, and z from the average positions (the difference between the average positions and the correct value.
  2. Next, calculate the x,y, and z errors for each of your points (each individual point, not the average position from above). Note, you'll have to make any negative distance errors positive so they don't cancel each other out. Make a nice table out of this and paste into Word.
  3. What are the minimum and maximum errors in x,y,z?
  4. What is the average error in x,y,z? Also, calculate the standard deviation of the x,y,z errors.
  5. Did the GLONASS or WAAS improve your signal? yes/no? How much? Why?

Now - to ArcMap. Bring the data in and plot it out. Zoom in so that you can see the distribution of the points. Create a quick layout, label the correctly positioned point. Plot it on top of the airphoto or any ole base map.

Hand in - the statistics (1-4), the layout, and a paragraph (5) which summarizes your results (how good in x,y,z, why, etc) and explains the accuracy implications- refer to your charts and layout.

3 points.