Which preposition to use with triangulates

from Occurrences 1%

This mountain, from its inaccessible position beyond our frontier, and in the midst of lawless Afghan tribes, had long been the despair of geographers, but Major Holdich with a small survey party had at length succeeded in ascending it, and was said to have triangulated from its summit over an area of 50,000 square miles.

Which preposition to use with  triangulates