System Effectiveness Model for Single Location Users

The System Effectiveness Model (SEM) for the Global Positioning System (GPS) provides users with a simple yet precise means of forecasting the availability and accuracy of GPS for any global location and for any date and time. WSEM36 provides the following information:

• Navigation accuracy by time, date, and region
• Dilution of precision graphs
• Satellite bearing/elevation graphs and tables for fixed sites
• Satellite elevation versus time graphs
• Satellite rise/set graphs for fixed sites
• Number of visible satellites for fixed sites

WSEM36 determines the satellite orbital parameters from almanac files and any current Notice Advisories to NAVSTAR Users (NANUs) from status history files. You must have these files before running the model. You may download all necessary files, including the WSEM36 application, by following the steps below.

1. Download the WSEM36 application. (EXE, 1.3 MB) System Requirements: Windows 95/98/NT.
2. When prompted, choose the save to disk option and save the file in the directory of your choice. (Make note of the directory for reference in step 3.)
3. Click the Start button on your desktop, then choose Run, followed by Browse. Locate WS36INST.exe in the directory you chose in step 2, select it, choose Open, and then choose OK.
4. The install program will prompt you to choose a directory in which to install the data files. By default, the files will be saved to the directory C:\Program Files\WSEM. You may choose a different directory if you wish, but note that the application file and the data files (step 6) must be installed in the same directory.
5. Open the Current GPS Almanacs and Status directory. (The directory will appear in a new window.)
6. Download each of the files in the directory. To download a file, right-click on the file name, choose Save Target As (Internet Explorer) or Save Link As (Netscape), and save the file into the directory you chose in step 4.
7. Once you have downloaded all of the data files in step 6, you are ready to run the WSEM36 application. Click the Start button on your desktop, then choose Programs, Wsem, WSEM36.

Once you have successfully installed the WSEM36 application, you can download the most recent GPS data files at any time by clicking the Current GPS Almanac and Status link on the GPS Satellite Almanacs and SEM Program page.

The WSEM36 application requires certain system files that are not included in some releases of Windows 95. If you have difficulty running the application, you may need to download and install OpenGL, which is available from Microsoft at ftp://ftp.microsoft.com/softlib/mslfiles/opengl95.exe