3 ms·

Googles solution sounds very familiar to what we used in the military: GRGs or geographical reference grids. Every point on earth was contained within a box na

Googles solution sounds very familiar to what we used in the military: GRGs or geographical reference grids. Every point on earth was contained within a box named with two letters. Within each box was a theoretically infinite number of digits that could be assigned. Practically, we had immense precision with as few as 8 numbers - 4 each for the horizontal and vertical axes on the map. While flying Close Air Support missions, we could be flying 30k feet overhead and within seconds have our sensors on whatever the ground controller wanted us to look at. It was a version of Lat/long, but far more intuitive with each digit representing a different order of magnitude of the base measurement unit.

stouset 9y ago
For those interested, this is the Military Grid Reference System (MGRS): https://en.m.wikipedia.org/wiki/Military_Grid_Reference_System https://en.m.wikipedia.org/wiki/Military_Grid_Reference_Syst...
colek42 9y ago
MGRS is a pain to program. So many edge cases.
- pouta 9y ago
  Can you elaborate? I'm really interested in knowing more...
  - colek42 9y ago
    Polar regions are tough, not many libraries support them. Lat/Lon represents a point, MGRS represents an area. This causes issues when converting between MGRS and lat/long and back again. Also, a single location can be represented by several MGRS coordinates since the numerical value is an offset from a line, the letters represent where this line is. Then we get into other issues. When converting from lat/lon we need to know what projection the data is in. I often have to make assumptions here, if my assumptions are wrong it could cause an error of many km, depending on how far away from the equator you are. There are several other edge cases I am probably no stating. If you are interested there is some pretty good sample code here: https://svn.osgeo.org/gdal/trunk/gdal/frmts/nitf/mgrs.c https://svn.osgeo.org/gdal/trunk/gdal/frmts/nitf/mgrs.c

stouset 9y ago

For those interested, this is the Military Grid Reference System (MGRS): https://en.m.wikipedia.org/wiki/Military_Grid_Reference_System https://en.m.wikipedia.org/wiki/Military_Grid_Reference_Syst...

colek42 9y ago

MGRS is a pain to program. So many edge cases.

pouta 9y ago
Can you elaborate? I'm really interested in knowing more...
- colek42 9y ago
  Polar regions are tough, not many libraries support them. Lat/Lon represents a point, MGRS represents an area. This causes issues when converting between MGRS and lat/long and back again. Also, a single location can be represented by several MGRS coordinates since the numerical value is an offset from a line, the letters represent where this line is. Then we get into other issues. When converting from lat/lon we need to know what projection the data is in. I often have to make assumptions here, if my assumptions are wrong it could cause an error of many km, depending on how far away from the equator you are. There are several other edge cases I am probably no stating. If you are interested there is some pretty good sample code here: https://svn.osgeo.org/gdal/trunk/gdal/frmts/nitf/mgrs.c https://svn.osgeo.org/gdal/trunk/gdal/frmts/nitf/mgrs.c