As it goes, Trespasser creates the massive terrain texture by rendering a combined version of all the large and small textured "terrain objects" and using this during gameplay. This all-in-one version of the texture only exists in the game itself and cannot be extracted with any utility.
To date, I've not heard of anyone successfully getting an all-in-one Tres terrain texture image. However, if you have skill or can get someone else who does to do it for you, in theory you could do it like this:
- In TresEd, click the landscape button or go to "Terrain > Draw Terrain Objects"
- Go to "Visibility > Select All"
- Go to "File > Export Selection as TPM"
- In 3DS Max, load the "tpmimport2.ms"* max script
- Use the script to import the TPM file you made earlier
- Set one of the viewports to "Isometric", so that no perspective is applied
- Zoom out to such a distance that the entirety of the terrain objects are visible (may take some adjusting)
- Render the scene from this viewport at whatever resolution you desire; I recommend allowing for a black (empty) outline around the terrain objects as a whole and then cutting it out in photoshop, afterwards taking steps to create image dimensions which fit what remains
*Trespasser's max scripts may be found on the main site or in the "MaxScripts" folder of Trespasser Twilight (linked in my signature)