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I apologise if I'm not using the right terms but I'm not a GIS expert.

This page has some GeoTIFFs (at least, I'm pretty sure they're GeoTIFFs) which I'd like to analyse and I have downloaded the first one:

http://data.ess.tsinghua.edu.cn/fromglc10_2017v01.html

When I open this file in an image viewer (e.g. PhotoShop) it opens as 8 bit greyscale. When I examine a specific pixel in, say, water (since that is visually obvious in the file) PhotoShop tells me the RGB values are (80,80,80). All other land cover values seem to follow the same pattern e.g. (29,29,29), (113,113,113) etc.

There is nothing on the previous page (http://data.ess.tsinghua.edu.cn/) that seems to give any indication of a "legend", or what type of land cover each RGB value in the GeoTIFF file maps to. I am assuming this is something commonly known or understood amongst GIS experts, but no amount of searching on this SE or google searching turns up any result. I even tried to look through the GeoTIFF standard but I couldn't see anything obvious there.

Is there somewhere I can get a breakdown of the RGB values in that file to common land cover types such as water, urban, forest etc.?

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    I suggest you have a look at the docx which is the topmost file in the link you posted.
    – Erik
    Commented Feb 5, 2021 at 9:19
  • @Erik That was the first thing I looked at :) The table lists land cover types but the numbers (10, 20 ... 100) don't make any sense in relation to the RGB values. For example, water is listed as "60" in that document - how does that map to "80"?
    – Arj
    Commented Feb 5, 2021 at 9:30
  • GIMP shows a 60 for a cell that I assume is water. Are you sure you clicked the right pixel? ;) It looks like the "level codes" in the DOCX and on data.ess.tsinghua.edu.cn are the values. Anyways, use a GIS like QGIS to look at GeoTIFF. That is data, not imagery an image viewer is used to.
    – bugmenot123
    Commented Feb 5, 2021 at 12:21
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    @bugmenot123 I definitely clicked the right pixel :) I appreciate your advice, but my original question still stands: is it possible to map land types (i.e. the "level codes" in the DOCX) to RGB values in the GeoTIFF using an image viewer, not GIS software. There are only 10 level codes, so I am prepared to go through the image files and map them manually (e.g. using the water example, the water level code of 60 maps to RGB (80,80,80)). But if there's a way to do this mathematically, I'd appreciate knowing how to do so, and I feel that it would be a valuable answer for this SE.
    – Arj
    Commented Feb 6, 2021 at 23:43

1 Answer 1

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OK so after a lot of messing around with some GIS software, the simplest way to do this is to open a GeoTIFF in PhotoShop (or any other image software) and set the mode to "Indexed Color" instead of "RGB Color". This seems to preserve the mapping of GeoTIFF data exactly, so that in this case water which is specified as "60" in the map layer table maps to an RGB value of (60,60,60) in the image software - i.e., the same as the index value. I hope this helps someone out.

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