The concept of mensuration isn't even close to being a secret; it's just arcane. You don't find a lot on google about it because it's really a niche subject, and google seems to want to redirect you to <ahem>, uh, "feminine issues not related to targeting". The key element is elevation data, combined with precise reference imagery. Here's a decent summary:^^And that's as much as we need to discuss regarding mensurated coordinates.
This post isn't so much for the guys with the info, but rather the guys with the questions.
"When engaging targets with PGMs,accurate target location, to include altitude, is paramount. (When targeting buildings, the feature height or a three-dimensional target grid is critical.)The target location error (TLE) is the key determinate of the risk to troops andcollateral damage estimate. Minimizing the TLE is the difference between atarget hit and a miss.Because even minor inaccuracies canlead to tragic results, most grids are mensurated. (Mensuration determines the exact three-dimensional target location by applying mathematical algorithms to compare two images within the digital point position database, or DPPDB, of the same terrain iteratively until they match.) For target mensuration, certain software must be employed for both planned and unplanned targets. Targeting specialists use systems based on the DPPDB, such as Dewdrop, Raindrop,and Rainstorm, to determine the most accurate target location. These assets are typically at the theater level, however, and are not practical for use against time-sensitive targets (TSTs)."
And from the "I learned something new today" bucket, if you go to slides 24-26 from this brief you can see how data from Litening pods or UAVs can be linked quickly to a laptop to produce mensurated points. Everybody wins!! :icon_tong
http://www.dtic.mil/ndia/2006psa_psts/kuz.pdf