Presagis

I am encountering an oddity when using uproject and project coordinates.  It appears as though Creator’s functions treat the origin of a UTM zone as an Easting of 0.0.  This is NOT the case, it should be 500,000.00

For instance, UTM zone 16 runs from 90W to 84W, with a central meridian of 87W.

a UTM Zone 16 coordinate of northing = anything, easting = 500,000 should result in a pure latitude conversion, with the longitude being 87.000000W

More to the point, if I set the database origin to 87.00000W, and put in a UTM easting of 500,000, the output of an “unproject” should be a longitude of 87.0000W

When I wrote my conversion routines, I compensated by subtracting 500,000 from all the easting values and that seemed to work to ge the correct lat lons.  I guess I will have to try backing them out of the projected UTM coordiantes as well.

FYI - there is no definitive easting = 0.0 point to reference an origin to, so I am confused as to the “right” thing to do regarding setting up appropriate db headers.

for now I will use the +-500,000 method, it seems to work.

The database origin is a local origin regardless of the projection.  If you want the UTM origin, when you do Convert Database Project, check the “Ignore Database Origin” box.  This will set the database origin to the UTM origin.

Ach - I see, it creates an origin at the equator where an easting of 0.0 would occur - at least it keeps me from having to do it offline or generate this location.

Yeah, UTM is funny.  “They” intechange the word “origin” with what is the “central meridian”, when origin implies 0,0 and the central meridian equates to an easting of 500,000.

I guess I’ll just have to decide whether I want to reference my UTM files tothe central meridian and keep the offset, or go with the false origin, which actually happens to be outside of the UTM zone it relates too 8*).  I’ll probably keep the central meridian, it is more deterministic and easier to compute, and is actually in the UTM zone.