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					                            Workshop #11
                    Global Positioning System (GPS)
Using the Trimble Planning Software

   1. First, download the latest version of the Trimble Planning Software from
      http://www.trimble.com/planningsoftware_ts.asp. Be sure that you download the
      latest Ephemeris file from the same
      page.

   2. Install the software to a computer on
      which you have the appropriate
      permissions.

   3. Start the Trimble Planning Software.

   4. On the Main Menu, go to
      Almanac>Import>SSF…

   5. Browse to the folder where you saved the Ephemeris file. Select it and click
      Open.

Setting the GPS Survey Parameters

   1. On the Main Menu, go to File>Station.

   2. Click on the City… Button to open the City Selector.


                              There are a number of options for selecting the area of
                              your survey. In this case, you will use the City Selector.
                              However, depending upon the area you will be surveying,
                              it may be more appropriate to manually enter
                              Latitude/Longitude coordinates, or to use the Map…
                              Button to search for a station visually.

                                  3. Select the world city that is closest to the area you
                                     will be conducting your survey in and click Select.

                                  4. If there are
                                      significant
                                      obstacles you will
      be confronting in your survey, click on the
      obstacles button and use the Obstruction Editor to
      define any obstructions you know will be a factor
      in your survey (will you be in a canyon, the


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   shadow of a mountain, etc?…).
5. Define the Starting Date/Time and Duration
   of your survey work.

6. Set the Time Zone you wish to have you
   reports formatted with.

7. Click OK




Creating Planning Graphs

Once your survey parameters have been entered, you can use the Trimble Planning
Toolbar to launch each of the graphs created by the planning survey.

   1. Click each of the Graph Buttons to launch its graph.

   2. On the Main Menu, go to Windows>Tile Vertically to view all graphs in the
      same window.

The most important Graphs are described briefly below…

Elevation

Satellites at very low elevation do not contribute very much to the calculation of a
position because of errors in propagating signals through the atmosphere. The
signals are also more susceptible to interference of multi-pathing. The Elevation
Graph shows the elevation in the sky of each of the satellites visible to a GPS receiver
in the area defined across the time period defined. Note that this window may be the
most important for those planning surveys in very vertically developed urban
environment.




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   Visibility

   This graph displays the visibility of satellites as a function of time.




   DOP (Dilution of Precision)

   DOP is an indication of signal quality that takes into account the number and position
   of satellites in the sky and in relation to each other. This graph is probably the best
   indicator of signal quality for planning a survey. The lower the DOP value, the better
   the signal quality.




Converting from Degrees Minutes Seconds format (DMS) to Decimal Degrees

If your GPS coordinates are in Degrees Minutes Seconds (for example 34°42'52"), you
must convert them to Decimal Degrees before using them in ArcGIS. To convert latitude
and longitude values from degree-minute-second (DMS) to decimal format, you can use
this formula:

                     degrees + (minutes*1/60) + (seconds*1/3600)




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Using GPS Data with NAD27 Data

   1. Open the Nad27_83_Compat.mxd Map
      Document from the Tutorial File.

   2. Add the track_line.shp layer (from the
      Shapefile folder) to the map layout.

   3. You will be warned about the Geographic
      Coordinate System differing from the layers in
      the map. Click OK.

   4. Right-click on the track_line layer and select Zoom to Layer.

Note that the track_line layer seems to run across some of the buildings in the Ortho
Photo. This is because of the differing Geographic Coordinate Systems, more
specifically, because the Datums they refer to are different. This causes and error of
about 20 meters north-south and 5 meters east-west in overlay of our data.

We need to transform the data to make it line up properly. For ArcMap to use WGS84
data in a NAD27 data frame, a Geographic Transformation must be applied to the data. In
the case of WGS84 to NAD27, this involves a mathematical calculation that inevitably
introduces a certain amount of error. Geographic Transformations between NAD83 and
NAD27 use a much more
precise “grid-based”
transformation. Therefore,
we will convert the GPS
track_line layer to NAD83
in order to apply the more
accurate transformation.

   5. Open the
      ArcToolbox and
      Search on the term
      “project.”

   6. Open the Project
      tool and select the
      track_line layer as
      the input.

   7. Save the Output as track_line_NAD83.shp

   8. Define the Output Coordinate System as NAD 1983 UTM Zone 18N.




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9. Select NAD_1983_To_WGS_1984_5 as the Geographic Transformation.

10. Click OK. You will get a Datum Conflict error message in the ArcToolbox
                                 results window, but the transformation will be
                                 applied.

                              11. The new projected layer will be added to your
                                  map layout. Note that it better reflects the “reality
                                  on the ground.”




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