Convert DOP into accuracy in meters

We use Reach RS with our own application. We want to know in what position is our machine and we want to have this information in our own application. We also want to have an information about GPS accurancy. And I know that this information is avaliable in Reach View app.
I also know that I can get an info about Dop to our own app. But can I convert DOP into accurancy in meter as You have in Your app?

I looking forward for Your opinion

1 Like

DOP numbers are without dimension by definition. So it is tempting to multiply them by a pre-defined scale’ and tell the world it is meters. However it is very tricky to convert DOP numbers to actual accuracies. There is no 1 on 1 mathemathical relationship between DOP’s and real life variances/accuracies. DOP numbers are good indicators on how usable the sattelliet constellations is to reliably/accurately compte fixes. For many purposes. As there are HDOP, PDOP, TDOP, etc. numbers… But please refrain from making them a scalable error indicator.

The accuracy produced by apps is usually tied to the closing errors of the position computation or something similar. Most RTK receivers can output their computed estimated errors to an external application. There are NMEA messages that can be used for instance. However be aware that those numbers are often ‘precision indicators’ alone. Precision with RTK is usually very high. Accuracy (that is precision + systematic errors) is often significantly worse than just the precision with RTK. In other words: Use the numbers that your receiver produces: But do not rely om them as absolutely true/correct.
Do not use DOP’s for error estimates.

Feel free to ask further.


Ok thanks a lot. We can use NMEA frames to log for error estimation instead of DOP, it is fine for us. Can You let us known, what frame type (GGA, GSA, etc…) We should use and what the indicator name should We use?

Standard GLL, GGA messages and such report back DOP’s. But many receivers (brands) have proprietairy messages and/or the actual output to the string can be changed. A generic message you can use is GST (Did not check if the reach has this string as an output, I must admit.)

Could you also tell me which arguments of GST frames to record?

You can check:

So you are most likely looking for arguments 6, 7 and 8.

Avialable of GST messages is depend on the ReachView version or somthimg more? I check it, We have the newest version of ReachViewer with GST messages and I check in docs that NMEA for Reach RS have GNGST messages. If I understand it well, then we should have a GST messages on our GPS?

I assume so. You might have to activate it in the menu.

This topic was automatically closed 100 days after the last reply. New replies are no longer allowed.