As you will see this method is not perfect. It will create some strange edges on the baseboards but you can fix this inside Trainz with the build-in tools.
I use for the GPS locations kuid2:70337:23016:10 Lat-Long reader. The GPS locations can be find using Goolge earth.
Other Trainz DEM tutorial https://docplayer.net/50509772-Converting-dem-files-to-trainz-maps.html
Other Trainz HOG tutorial https://freepages.rootsweb.com/~wewain/misc/trainz/Surveyor/Baseboard/Topology/TerrainGeneration/Downloading-HOG.htm
Microdem program https://www.usna.edu/Users/oceano/pguth/md_help/html/download_md.htm
Trainz HOG program https://trainz.luvr.net/projects-view.php?pid=390&tab=f
DEM download .HGT files: http://viewfinderpanoramas.org/Coverage%20map%20viewfinderpanoramas_org3.htm
TransDem payware http://www.rolandziegler.de/StreckeUndLandschaft/startseiteTransDEMEngl.htm
<kuid2:70337:23016:10> Lat-Long reader ==> download on Trainz download station.