Lat/Long to cartesian (And the other way too)
Jon Witte
Hello, all.
My problem...
I've scanned in a Transverse Mercator Projection map of the UK, and
thrown it in a picture box. Moving the mouse pointer around gives me a
cartesian value for cursor position that I want to convert to a
Lat/Long. I also have some points as Lat/Long that I would like to
display on the map.
My maths is (very) rusty, so before I sit down and work this out from
first principles, can anyone help!
TIA
Jon Witte
Gary Ardell
Jon,
See,
http://wwwhost.cc.utexas.edu/ftp/pub/grg/gcraft/notes/mapproj/mapproj.html#TM
Unfortunately, it seems you've chosen an extra confusing scaling system to scan. (A simple Mercator projection
would be much simpler. Longitude is linear and latitude goes as the integral of 1/cos(y). ) Plus, scanning
of paper maps often introduces some annoying non-linearities and alignment problems.
My advice would be to build a table with the Cartesian and geographic coordinates of the four corners of the map
plus 10 to 25 strategically chosen landmarks. (Atlases often have a table of the lat/longs of all the cities in the
area.) Then for any point you can simply find the nearest surrounding neighbors and interpolate. If you need to speed
this process up, you can pre-calculate the lat/long of every pixel of the map and store it in a table.
Good luck,
Gary