State Plane Coordinates
vs. Surface Coordinates, Part 7.
by James P. Reilly, Ph.D.

In this column I’m going to show how to start a traverse using state plane coordinates. Before that, let’s go online to the home page of the U.S. National Geodetic Survey (NGS) and locate a software program that converts geodetic coordinates to state plane coordinates. I’m doing it this way because most readers of this column have access to the Internet at home. I’m not going to show all web pages leading to the software, just the pertinent parts that get us to the conversion software.

Figure 1. NGS Home Page

The Internet address for the NGS is www.ngs.noaa.gov. Once the home page loads, click on Products and Services, a link in a list of links along the left side of the page under the header Site Contents. Scroll down the Products and Services page and click on the link for Geodetic PC Software Programs under a bold Software header. This will take you to a page with another Geodetic PC Software Programs link; click on it as well. Scroll down the next page and click on the SPCS83 (Version 2.0) link.

This will bring you to a page headlined Current directory is /pub/pcsoft/spcs83. Scroll down through the warnings until you find these three files: spcs83.doc, spcs83.exe and spcs83.for. Download these files by clicking on them.

Figure 2. Sketch of Sample Problem.	Station Name	Latitude (North)	Longitude (West)
	Bromilow	32 16 52.33969	106 45 15.77636
	Reilly	32 16 55.93458	106 45 15.16429
	Wakeman	32 17 00.10142	106 45 29.49809

Figure 2 is a sketch of the sample problem. There are three stations, all established using GPS. NAD 83 geodetic coordinates for each station are given in the figure. We will use SPCS83 to calculate the state plane coordinates for each station.
With SPCS83 ready on your computer, do the following:

1. SPCS83 is a DOS program; the executable file is SPCS83.EXE. Type spcs83 and hit the enter button.

2. You will see the following:
       *** PROGRAM SPCS83 *****
       VERSION NUMBER 2
       LAST UPDATE 06/27/88
   DO YOU WANT TO COMPUTE:
   GEODETIC POSITIONS TO STATE PLANE COORDINATES STATE PLANE COORDINATES TO GEODETIC POSITIONS PRINT THE OUTPUT FILE ON THE PRINTER TYPE NUMBER

3. Type 1, hit the enter button.

4. The following line will appear:
   DO YOU WANT TO RUN INTERACTIVELY (Y/N)?

5. Type Y, hit the enter button.

6. The following line will appear:
   DO YOU WANT THE OUTPUT SAVED IN A FILE (Y/N)?

7. Type Y, hit the enter button.

8. Give a name to the output file. It should be no more than eight characters. Then hit the enter button.

9. Follow the instructions on the screen for entering latitude and longitude. When asked for direction of longitude, enter W, for west longitude.

10. The last question asked is
    ENTER ZONE CODES, AS MANY AS THREE

Figure 3. State Plane Zones

Figure 3 shows zone codes for each zone of every state. In our example, the zone is New Mexico Central, zone 3002. (We only have one zone in our sample problem.)

11. Repeat this procedure for every station. At the end, print the output file. For our sample problem, the output file is shown in Figure 4.

We are now ready to traverse on the state plane grid. Looking at Figure 4, we input the latitude and longitude, on the 1983 datum, for stations Bromilow, Reilly and Wakeman. The output for each station are the northing, easting, convergence and scale factor. (We haven’t discussed convergence, that will be in the next, and last column, of this series.) This is what we are looking for: Inversing between each pair of coordinates gives the grid distances. Taking the coordinate differences leads to the grid azimuth. From the differences in grid azimuths we get horizontal angles. We will do all these calculations, and more, in the next column.

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James P. Reilly serves as head of the Department of Surveying at New Mexico State University, College of Engineering, in Las Cruces.