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I don't even no where to begin... I am involved with a group that is in Ethiopia and the want to set geodetic control.  They have access to a trimble R8-2 and TSC1.  What is the process like...I mean I understand the post processing in the States, but I have no idea what the process is outside of the USA.


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  • Great help from all...thank you for the guidance and feedback.
  • Dear Sir,

    It’s my pleasure to send my suggestion on basic geodetic reference control point input for geodetic/supplementary survey works in Ethiopia.

    You can get CORS, Zero Order, 1st order etc basic control points data either from shelf, depending on your project location, or you can get service to establish (GPS surveyed and processed) for a particular project from Ethiopian Mapping Agency, the only national mandated organization to make, archive, manage, administer, disseminate, regulate and assure quality of geo-spatial information (fundamental geo-spatial data set) throughout Ethiopia.   

    With Best Regards

    Girma Habtegiorgis

    • If any addtional question please do ot hesitate.

  • You need reference (base) GPS data from a known point. If there is no control points with known coordinates, you can try to use either the NGS's OPUS service or the Australian AusPos.

    In this case you need to collect enough raw data on the point you have to use. Enough means several hours, because NGS and AusPos will search for the nearby known GPS base stations, but sometimes the closest is 500-1000 km far from your point. The longest your data is the best chance to get fix position from the mentioned services. 4 hours was enough for me to calculate a vector from Hongkong to Hanoi (800 km), but 12 hours was not enough from Bahrain to Tehran (1100 km)

    The logging rate must be about 1 per minute, or 1 per 3 minute if you want to use these external services.

    If you can find base stations closer to your point, and you are processing the data with your own sw. such as Trimble TBC, you need to log raw GPS data at the same rate which the Reference stations are using (1/sec..1/15sec, etc), and the length of your data may be shorter (30 minutes if the base is 10-20km far from you, 1 hour if the base is 30-50 km, etc.)

  • This has some useful info. Might be the place to start.
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