Great free software for calculating your GPS accuracy (DOP)!

In the last blog, I gave an introduction to dilution of precision or DOP and explained when you need to know it and when you don’t. This time, I want to show you a very cool, free program to calculate your DOP values throughout the day. All you need to know is your latitude and longitude and day. The program is called “Planning” and is from Trimble. You can download it here.

To use this program, you need to first enter your position through File > Station. You can use the map feature to get ‘close’ but you really should use the correct latitude and longitude. On this screen, you also set the date and time and duration of observation. Then, you need the satellite almanac information. This is downloaded from the Trimble site as an ‘.alm’ file or you can use an ‘.ssf’ file.


Here we see a plot that shows the total DOP at 10 minute intervals for San Diego (where it is very lovely right now). Looks like 7:30 a.m. is the time to work.

That’s it! Now, play around with the different map features, it is surprisingly easy to navigate. Notice that you can use GPS (United States system) or Glonass (Russian system). WAAS is available but since those satellites don’t affect the DOP, they are not included in the almanac.


This cool screenshot shows the visibility of each satellite throughout the time period. You can turn satellites off and on to clean up the graph.

But wait…if the DOP is based on satellite positions, what happens if you cannot see a particular satellite because of mountains or buildings? Obviously, that satellite is no longer used in calculating the DOP. The “Planning” software doesn’t directly allow you to blank out areas of the sky (but you can turn off certain satellites). However, there is another great program that allows you to show the blocked view based on topography. Stay tuned…


Explore posts in the same categories: GIS, GPS, Mapping, software

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One Comment on “Great free software for calculating your GPS accuracy (DOP)!”

  1. Julian Says:

    Actually, the planning software does allow you to create obstacles around your station. You’ll need to set up a station position as normal and then click on the Obstacles… button. This will allow you to ‘paint in’ the horizon seen from that station, which may include mountains, buildings, or trees, etc.

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