Global Mapper v25.0

What is the Difference between Arc 1960 and Arc_1960

btl_kq
btl_kq
in Projection Questions
Good day all

I am having  a problem with reference datum Arc 1960. There seems to be another one in Global mapper which is Arc_1960. What is the difference between these two? Which of them is the correct one, there seem to be about 2.4m shift between them. Can any one help please with advising which one is the correct one to use?

Clarence

Answers

  • geomannie
    geomannie Global Mapper User Trusted User
    edited November 2018
    Hi,

    I used to work widely across East Africa I was never very sure what people meant when they stipulated that the datum Arc 1960 were to be used. Each country seems to have its own flavour of this datum, similar but slightly different, and the specific version is almost never sepecified (e.g. https://microem.ru/files/2012/08/GPS.G1-X-00006.pdf) and . For my work it wasn't critical but I can see where it would become so.


  • btl_kq
    btl_kq
    Thanks

    If it was my choice this Arc1960 thing would have to be removed  just as it is for LOS system in Zimbabwe,  we would be better off to stick to WGS84.

    Why I have raised it is because, I am processing drone data with Pix4D and the key outputs are point cloud file and Orthomosaic image, but Pix4D seems to favor writing into the header two different  Arc 1960 for each of the files. It is injecting the typical Arc1960 into LAS file so when I load it Global Mapper it appears to line up with my GCPs perfectly, but when I load the Orthoimage, it is shifted north by 2.4m off the GCPs and point cloud.  When I looked into the metadata for each of the files, I see that the LAS file is using Arc1960 and the Orthoimage is using Arc_1960. If I change the one from Arc_1960 to Arc1960, everything lines up. But I am still keen to know why are there two? Global mapper software has both of the listed too, older versions did not have. 


  • Richard_Muraba
    Richard_Muraba

    Hi, a user from Kenya. I can confirm that Arc_1960 is incorrect while Arc1960 without the underscore is correct. This is based on overlaying with ground survey data and data from other software.

    The Arc_1960 gives us problems as it may be unknowingly selected by the user, introducing a 2.4m shift to data.

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