Some scripts to sample quadratic patches from given real-world heightmap data.
Data source: https://www.eorc.jaxa.jp/ALOS/en/aw3d30/index.htm

Download the GeoTIFFs of your target area from the source above and place the folders in a root directory (In this case /SSD/Datasets/Terrain/ ). Execute the RunSampler and put this root directory to the first argument to get equal-sized sample patches.

./RunSampler ROOT_DIRECTORY_OF_ALOS_DATA DESIRED_PATCH_SIZE_IN_KM NUMBER_OF_SAMPLES_PER_PATCH

-o: Output directory
-s: Size of output patches in pixels
-d: Enable debug mode

./RunSampler /SSD/Datasets/Terrain/ 10 150 -o ../output -s 256 -d
Result: 150 patches of real world size of 10x10km and pixel size 256x256 for each GeoTIFF in /SSD/Datasets/Terrain/