On 12/9/24 3:06 PM, Javier Jimenez Shaw via PROJ wrote:
What always make me nuts is the false easting and northing. They are just to have positive numbers in your coordinates (it is just adding an offset to the final numbers). I am never sure if they are "real" meters or "distorted" meters (I think the latter).
I sympathize! However there's a sound reason for having all the coordinates positive, namely computing their differences is more systematic. If one of the numbers is negative you have to switch to the rules for addition. (We're talking about hand calculations here, of course.) I'm old enough to have used log tables and there was a similar notational trick here. Thus log(2) = 0.3 (these are common logs) and so log(0.2) = 0.3 - 1 = -0.7. But when multiplying a bunch of numbers, i.e., adding a bunch of logs, you don't want a few of them to be negative. So log(0.2) was written either as bar1 . 3 (bar1 means -1 only in the units place), or 9 . 3 (10 added to negative logs) [Yes, the false easting and northing are distorted meters.] -- Charles Karney <kar...@alum.mit.edu> 702 Prospect Ave Princeton, NJ 08540-4037 _______________________________________________ PROJ mailing list PROJ@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/proj
