Howto put your real world data terrain into google/mymaps. Example PMC ArmA 3 Terrains - Google/MyMaps.

Step by step:

1. open global mapper project
2. make sure only the user created feature grid box of your terrain is visible, file → export → export vector/lidar format → select export format KML/KMZ. use default export options values
3. go to Google/MyMaps and login (yes you have to login, sorry)
4. click big red/orange button; create a new map
5. mymaps untitled layer click import link, choose a file to import → upload → select a file from your computer → browse to your new KMZ file you created with global mapper
6. click the new untitled polygon shape, it selects your new KMZ area
7. click the new dialog style paint bucked icon, choose red color, set polygon transparency and border width to your liking
8. click edit pencil icon, set a terrain name here
9. now you can click and hold down LMB, then drag the terrain from untitled layer into any layer you prefer (you must create new layers of course)
10. use share to set so other users can view your mymap link without needing to login

The projection between UTM local and google mymaps might skew the terrain box a bit.

On the shared mymaps link, the last bit of “z=?” is the zoom level.