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Resolution (GSD) for photogrammetry (3D mapping + DSM)

Posted by Lui Habl on March 25, 2016 at 10:38am

Hi everybody,

I am starting to plan the construction of a small plane to do photogrammetry, in special to do 3D mapping and the DSM.

I'm stuck in two questions:

  • What is the resolution that you need to do, for example, a topographic map? 

I saw some application and people used most of the time 1 to 5 cm of GSD, but is there any technical explanation or rule of thumb for this?

  • Is it necessary to have an oblique camera to do 3D mapping or it is enough to have just the one facing downward? 

If is necessary, what usually is done? You put two cameras or do the survey two times changing the position with a gimbal?

Thank you a lot!

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Tags: 3d, dtm, maps, photogrammetry
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Replies

  • Vusal Jalilov March 27, 2016 at 11:57pm

    Hi Lui, 

    In response to your 1st question, please, note that since historically topographical maps were printed on paper the "resolution" (density or level of details) was identify based on their scale.

    Links to good articles and tools on this matter are below

    Relation between printing scale and GSD

    Ground Sampling Distance (GSD)

    TOOLS - GSD Calculator

    Focal length and flight altitude vs Ground Sampling Distance

    (you may or may not need to sign-up)

    As for the 2nd question, camera only in NADIR position (facing downward) is enough for 3D mapping (DSM, DTM, Orthophoto Map). However, if you need to do a 3D scan of a building or structure or a tower, then you must use an oblique camera and take photos flying around a structure in circles of incremental heights.

    More on this below:

    Vertical / Oblique imagery

    Image Acquisition Plan

    Regards,

    Vusal

    Relation between the printing scale and the GSD
    When the final output has to be printed, the printing scale has to be defined. Typical output to be printed is the orthomosaic as it serves as a map.…
    • Lui Habl > Vusal Jalilov March 28, 2016 at 7:52am

      Hi Vusal,

      Thank you for the information, it helped a lot!

      Best regards,

      Lui

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