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Can anyone please explain me the terrain elevation issue that I am facing?

Discussion in 'World Building' started by franziskusb, Aug 26, 2021.

  1. franziskusb

    franziskusb

    Joined:
    Apr 22, 2021
    Posts:
    2
    When I import a RAW grayscale heightmap for a terrain layer I am facing the issue that only the lowest and highest points of the terrain have the expected height, but heights in between are off.

    I tested this by placing little cubes according to the geospatial data that I am working with. There I saw that there always is a big difference between the cubes and the actual terrain.

    My workflow is the following:

    I open the ASC-File containing the terrain data in QGIS (tool for geospatial data)
    -> I export a rendered grayscale TIF file from QGIS
    -> opened in Photoshop
    -> changed image size to 4097x4097 and set the mode to 16-bit grayscale
    -> exported as RAW file
    -> imported as terrain heightmap in Unity
    -> set y coordinate of the terrain to the lowest height of the terrain which is shown in “QGIS” and for the terrain height I used the difference of the highest and the lowest elevation

    You can find the relevant files on my googledrive as they were to large for upload on the
    https://drive.google.com/file/d/1zjwLPxe7jT5SNuT-iwUBSIiWoqT5FKXO/view?usp=sharingforum.

    I also tried directly creating the RAW file from the ASC file using the tool “GDAL” but this resulted in a completely flat terrain.

    I would really appreciate it if someone could help me. I am struggling with this for quiet a while and I really must solve this as it is very important for my bachelor thesis.
     

    Attached Files:

    Last edited: Aug 26, 2021
  2. Kurt-Dekker

    Kurt-Dekker

    Joined:
    Mar 16, 2013
    Posts:
    18,311
    I theorize it might be non-linear colorspace when you make your TIF file.

    You might want to make a test grayscale with a series of height areas, such as 0%, 10%, 20%, up to 100%, then import it, and from within your Unity scene you can see how that imports and reason if something along the way is applying a non-linear function.
     
  3. franziskusb

    franziskusb

    Joined:
    Apr 22, 2021
    Posts:
    2
    Thank you a lot for your reply! @Kurt-Dekker

    I really appreciate it that you are trying to help :)

    I created two 33x33px raw files in photoshop. One with 100%, 80%, 60%, 40%,20% and 0% gray and a second one with a linear gradient from 100% to 0%.

    You can see the results in the attached image.

    With the second gradient you can clearly see that there is some non-linear function applied.
    I am wondering what I could now do to solve the issue and I am surprised that I am nearly the only one who is struggling with this. Maybe it's due to the fact that you only notice the issue when you are doing measurements like I do...

    Any further ideas what I could do?

    There was already someone who experienced the same issue back in 2016 but no one replied.
    https://answers.unity.com/questions/1188501/terrain-heightmap-non-linear-mapping-issue.html
     

    Attached Files:

  4. Kurt-Dekker

    Kurt-Dekker

    Joined:
    Mar 16, 2013
    Posts:
    18,311
    Perhaps try correcting it the way you would correct gamma?

    https://en.wikipedia.org/wiki/Gamma_correction

    You might even be able to find the actual terms used in your TIF step (or wherever the gamma is being introduced) and back it out perfectly.
     
  5. HIBIKI_entertainment

    HIBIKI_entertainment

    Joined:
    Dec 4, 2018
    Posts:
    141
    This is interesting.

    My thoughts are if Unity terrain reads aren't working in IEEE 754 format 32-bit floats on the raw data OR, are not using height/width ratios to support the human perception of mountains.
    then the Y vertical calculations is using a perfect cube for the "volume bounds"

    i know from experimenting a long time ago with the brushes, the resolution and density wasn't always accurate to the unity given in the brush. unless the terrain was at a certain width.
     
    warthos3399 likes this.
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