Trying to make a modified map of South America with real-world height data

[Coriolis]

I'm trying to create a map of a future, post-apocalyptic South America with elevated sea levels and some topographical changes, but I want to start with present-day South America height map as a baseline, and I'm having a lot of problems with that.

My tools are GIMP (2.8 is my preferred, but I have 2.10 and can use it), WILBUR, and Inkscape (which I use for icons and labels, not much use for this part of the process)

I've been trying to pull USGS data from Earth Explorer, and while I've tried multiple data sets, the only one that includes all of South America and isn't ludicrously over-defined (I'm wanting to make an image that's no more than 3300x5000 pixels) is GTOPO30. This data can come in two formats: DEM and GeoTiff.

DEM doesn't work with GIMP. I get some layers, but nothing I can use as a height map. I'm not sure what program I could use to play with DEM.

Geotiff is really finicky with GIMP; it doesn't work at all with GIMP 2.8, and even 2.10 sometimes refuses to open it, and cites errors when it does. That said, I did manage to open the four source map images, stitch them together into a coherent 9,600x12,000 pixel map, and shrink it down to something manageable. Problem is, the height map is almost a pancake. The difference between lowlands and mountaintops is barely noticeable.

South America Real Life.png

So I tried using the Color Curves tool to make the elevation differences more pronounced, which helped, but this yielded a tiered look to the terrain, and most of the continent appears totally flat and at the same elevation. This is a problem, especially when I want to play with sea level effects on the coasts; it means that either the coasts aren't going to be affected, or most of the continent will be underwater.

South America Attempt 1.png

So this is my problem: I need a way to get height map data for South America that I can open with GIMP and that uses the full spectrum of black to white to define heights.

I haven't found any good tutorials that seem to cover this. Any ideas?

[Turambar]

I'm trying to create a map of a future, post-apocalyptic South America with elevated sea levels and some topographical changes, but I want to start with present-day South America height map as a baseline, and I'm having a lot of problems with that.

My tools are GIMP (2.8 is my preferred, but I have 2.10 and can use it), WILBUR, and Inkscape (which I use for icons and labels, not much use for this part of the process)

I've been trying to pull USGS data from Earth Explorer, and while I've tried multiple data sets, the only one that includes all of South America and isn't ludicrously over-defined (I'm wanting to make an image that's no more than 3300x5000 pixels) is GTOPO30. This data can come in two formats: DEM and GeoTiff.

DEM doesn't work with GIMP. I get some layers, but nothing I can use as a height map. I'm not sure what program I could use to play with DEM.

Geotiff is really finicky with GIMP; it doesn't work at all with GIMP 2.8, and even 2.10 sometimes refuses to open it, and cites errors when it does. That said, I did manage to open the four source map images, stitch them together into a coherent 9,600x12,000 pixel map, and shrink it down to something manageable. Problem is, the height map is almost a pancake. The difference between lowlands and mountaintops is barely noticeable.

South America Real Life.png

So I tried using the Color Curves tool to make the elevation differences more pronounced, which helped, but this yielded a tiered look to the terrain, and most of the continent appears totally flat and at the same elevation. This is a problem, especially when I want to play with sea level effects on the coasts; it means that either the coasts aren't going to be affected, or most of the continent will be underwater.

South America Attempt 1.png

So this is my problem: I need a way to get height map data for South America that I can open with GIMP and that uses the full spectrum of black to white to define heights.

I haven't found any good tutorials that seem to cover this. Any ideas?

A couple thing. First in Gimp, you can use levels to set the highest and lowest values as black and pure white respectively, which should help with contrast (make sure your DEM is as high resolution as possible for best effect).
Another thing you can do, is pull the DEM into a program like Gaea to add texture to it before working it in Gimp. For example I actually did a quick experiment with South America not long ago:
SA map.png

[Coriolis]

A couple thing. First in Gimp, you can use levels to set the highest and lowest values as black and pure white respectively, which should help with contrast (make sure your DEM is as high resolution as possible for best effect).
Another thing you can do, is pull the DEM into a program like Gaea to add texture to it before working it in Gimp. For example I actually did a quick experiment with South America not long ago:
SA map.png

Thanks for the tip with the levels setting. The result is much better.
South America Experiment 2.png
It's still not quite perfect; it's very steppy at lower elevations, but it's much more workable than what I had before. This might just do the job.

[Redrobes]

QGIS can handle many types of file format related to height maps but I am not personally familiar with the one your using so cannot comment. DEM is more of a classification of many file formats. For example ArcASCII is a common one for height maps but there are many. For GeoTIFF I think it should handle that one and there are other apps which can too. If you have more problems then post the URL link to the earth explorer with the settings that you want from the data - or upload the DEM data file in a zip file here and ill take a look. We can host ZIP files and I believe USGS data is public domain.

[Coriolis]

QGIS can handle many types of file format related to height maps but I am not personally familiar with the one your using so cannot comment. DEM is more of a classification of many file formats. For example ArcASCII is a common one for height maps but there are many. For GeoTIFF I think it should handle that one and there are other apps which can too. If you have more problems then post the URL link to the earth explorer with the settings that you want from the data - or upload the DEM data file in a zip file here and ill take a look. We can host ZIP files and I believe USGS data is public domain.

Thanks for the help! The specific site I'm using for download is https://earthexplorer.usgs.gov/
The specific data sets I've tried playing with are the Digital Elevation category, and the specific data I used was GTOPO30. There were four source images I downloaded for South America:
GT30W100S.tif
GT30W100N.tif
GT30W60S.tif
GT30W60N.tif

If you think we can do better than what I tried with adjusted color levels, please do share, and thanks for the help!

[johnvanvliet]

For Goe-tiff's i use Nip2 ( a GUI for the vips image library )

install vips first
https://www.libvips.org/
windows binarys are here
https://github.com/libvips/build-win...es/tag/v8.13.0

then the GUI nip2
https://github.com/libvips/nip2
a Microsoft windows binary is here
https://github.com/libvips/nip2/releases/tag/v8.7.0

nip2 is almost a cross of excel and gimp , and takes some getting used to

for the Earth data you will want to " normalize" the 16 bit data from height in meters to the full 65536 data depth
to do that use the nip2 math functions

find the min. value
subtract the min. value
find the max. value
and divide by the max.
add a number ( 65536 )
and multiply

then convert to 16 bit unsinged integer and save

[waldronate]

GTOPO30 is 30 arcsecond resolution (about 1km) and ships in tiles. ETOPO1 is 1 arcminute resolution (about 2km) and ships in a single file, including ocean depths (bathymetry probably doesn't matter for this project). GTOPO30 was questionable in some areas and ETOPO1 was better in quite a few places.

A few years back - 11 years, it looks like - there was a discussion on importing the ETOPO1 data set into ProFantasy's Fractal Terrains product over here at ( https://forum.profantasy.com/discuss...at-with-etopo1 ) if you're interested. The settings are what's important and the same import tricks will work in Wilbur. Recoloring directly in Wilbur will work, as will using Wilbur to do things like adjusting spans and saving to a few common image formats and adjusting water levels.

The quick version from ETOPO1 directly into Wilbur with one import:
e0.jpg

In Wilbur:
File>>New, Width=21601, Height=10801.
File>>Open, Pick your flt file name, THEN pick "Binary Surface (*.bin)" as the type and click Open.
On the dialog, set Type=4 byte, float; LSB first, not Signed, Line Width 21601, Header Length 0 bytes. File Block - XStart=0, Y Start=0, Width=21601, Height=10801. Memory Block - Width=21601, Height=10801.