Question

Hi,

I've been playing with the above app to try and get a handle on using GPSTk to do DOP Calculations for an app I need to develop and I am getting a number of very bizarre results. I have loaded a SEM Almanac and a RINEX obs file, firstly it shows an Ephemeris Initial date of 2205 and then I get DOP values that range from 0 to over 2 million...I am unsure as to what is going on andwhy teh values are so extreme. I was expecting DOP values between 1 & 20 not 0 & 2000000+. Can anybody help?

Thanks, Calum

-- CalumMacLean - 22 Feb 2012

Answer

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Hi Calum,

If you haven't done this already, run DOPcalc without parameters to check on input parameter requirements, options, and formats. Also, when you do run the app, you may want to increase the debug level or verbosity (again, check parameter list for these) as you look for the cause of the problem.

If you can provide certain information about your usage and environment, that could be enlightening. Specifically, if you would provide:

-- exact command line usage with parameters -- what platform/OS you are using -- which type of GPSTk distribution you're using (built from trunk checkout, built from downloaded zipped source file, pre-built downloaded zipped file for your OS, e.g.) -- which version of the GPSTk you're using (1.7, trunk(=1.7+), other)

That should get us started -- if you find your problem source is the data, or if you solve it with parameter check or debug output, please let me know. Good luck!

Best Regards,

-- Susan Cummins

-- SusanCummins - 23 Feb 2012

Hi Susan,

Thanks for the speedy response. I am running on RHEL 5.6 on an HP Z400 using GPSTk 1.6 source ( I didn't download it so I can't tell you much else about the version of GPSTk). I have tried various ways of running the app but basically I am using this as the basis of my command line:

DOPcalc -e /share/current_sem.al3 -o /share/usno0200.05o

I have tried with debug on full (-d -d -d -d) and verbosity on (-v) I have also tried specifying the location rather than taking it from the RINEX Obs file (-p "X Y Z"). I have also added some extra logging and noted that the return codes from PRSolution::RAIMCompute and DOP::Compute are not being checked and are indicating errors in the calculation / insufficient data. I have to admit that the SEM and Obs files IO am using are not recent, could this have such a dramatic effect on the results?

Cheers, Calum

-- CalumMacLean - 28 Feb 2012

Hi Calum,

What is the format of your obs file data? RINEX? USNO? Of these two, only the RINEX format will be supported under DOPcalc (RINEX 2). The other formats supported are listed along with the required input parameter info when running DOPcalc without parameters, as you may already be aware. I'll pursue this further here as time allows, please let me know if you discover issues with the data.

Best Regards,

-- Susan Cummins

-- SusanCummins - 01 Mar 2012

Hi Susan,

I've been using RINEX obs files.

Regards, Calum

-- CalumMacLean - 05 Mar 2012

My biggest issue is that I want to be able to do the DOP calcs without any obs files, simply using teh position of a receiver (lat, lon, alt), date & time and the almanac file...mathematically I knwo this is possible, just can't find any way to do it in GPSTk....

-- CalumMacLean - 05 Mar 2012 No such template def TMPL:DEF{PROMPT:supportquery}

Topic revision: r6 - 05 Mar 2012, CalumMacLean
 

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