GEOG 488
Acquiring and Integrating Geospatial Data

Bringing GPS Data into a GIS

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A. Download the Lesson Data

My story:

If you recall, one of the layers that the State College Borough Water Authority identified on their GIS wish list was fire hydrants. I decided to acquire hydrant data for this activity even though that type of data may call for sub-meter accuracy, something my recreational grade Garmin eTrex receiver will not give me. I noticed that there are some new developments in Pine Grove Mills that aren't included in the CAD data yet. Acquiring features in new developments is a great use for GPS.

NOTE -- If you are going to be collecting data in neighborhoods or in some place where your activities may look suspicious, it is a good idea to let the police department know where you will be and what you are doing in case someone calls. In these days of heightened security awareness, I suggest that you stay away from obvious military or government facilities.

Registered Students download from ANGEL the Lesson 7 data (lesson7files.zip) to a new folder (e.g., C:\MGIS\GEOG488\Lesson7). This .zip file is about 73 mb.

B. Load the Basemap and GPS Data

We will be overlaying the GPS data I acquired with some of the county basemap data you've seen in previous lessons.

  1. Add the streets layer first. The data frame will assume the projection of that layer.
  2. Add the digital orthophoto clip_9230a.tif.
  3. Add the PGM_hydrants layer. These are the hydrants I acquired with the GPS. My receiver units are: Position Format: degrees, minutes, seconds; Map Datum: WGS 84.
  4. Rather than adding attributes directly into the GPS unit, I took notes in the field, being sure to include the waypoint number with each hydrant number. I personally always keep a data log incase of subsequent problems with the unit. Add the hydrants_lookup.dbf table into ArcMap.
  5. Join the hydrants_lookup.dbf table to the PGM_hydrants layer using the waypoint number for the join.
  6. In the next section, you will be adding fields and populating them. Export this layer to make the join permanent. Give the layer a new name such as PGM_hyd_ids.
  7. If you zoom around the ortho, you can see that one hydrant I acquired (z2-10-05) is in a development that was put in since the aerials were flown.

C. Add X and Y Coordinates

You'll notice that the X and Y coordinates are not included in the table.

  1. Open the Attributes of PGM_hyd_ids table.
  2. Add fields to hold the coordinates, e.g. X_coord and Y_coord. Be sure to specify parameters that will be able to hold the values, e.g. type: double, precision: 10, scale:6
  3. Right-click the field heading for the X field and click Calculate Geometry.
  4. Calculate the X Coordinate of a Point
  5. Right-click the field heading for the Y field and click Calculate Geometry.
  6. Calculate the Y Coordinate of a Point

D. Compare GPS Coordinates to a Known Location

  1. Add the benchmarks layer. These are benchmarks from the National Geodetic Survey site [http://www.ngs.noaa.gov/].
  2. Add the digital orthophoto clip_9243c.tif.
  3. Add the psu_ngs layer. These are GPS points I collected for one of the NGS benchmarks on the PSU campus.
  4. Measure the distances between the collected points and the benchmark with known coordinates. The 16 locations I acquired are off between 2 feet and 15 feet - not bad!

Now, you will be given some instructions on how to acquire these benchmarks from the NGS site to test the accuracy of your receiver.

E. GPS a National Geodetic Survey Control Station

  1. Go to the National Geodetic Survey site [http://www.ngs.noaa.gov/].
  2. Click the datasheets link.
  3. Click the Shapefiles button.
  4. You can pick from any of the Retrieval Methods, but these instructions will be for a Radial Search.
  5. Enter a Center Latitude and Center Longitude. These can be acquired with your GPS receiver.
  6. Enter a Radius.
  7. Keep the defaults for Data Type, Stability, and Compression Options.
  8. Enter a File Prefix and click Submit.
  9. A list of stations should appear. Highlight the stations you want to download or click Select All and click Get Shapefile.
  10. Save the file to your Lesson 7_8 directory. Unzip the file and add the shapefile to ArcMap.
  11. Now, you should now GPS these stations to see how accurate your GPS data are.

F. Optional Go Further into GPS and Location

Here is a look at geodetics and GPS

That's it for Part I!

You have just completed Part I of this module, which involved looking at acquired GPS data and adding X and Y coordinates. In Part II, you will load GPS data you've acquired.