[OSRS-PROJ] Horrors of --- Krovak projection
Gerald I. Evenden
gerald.evenden at verizon.net
Wed Feb 19 11:59:54 EST 2003
This is just a short note on the status of the Krovak projection.
The forward projection appears to be working in its native
math-based mode. Tests for conformality with the -V option
show it is OK. Math-correct x-y are in the -x -y quadrant
for Czech geographic coordinates.
Currently the execution script looks like:
<S-JTSK> +proj=kocc +ellps=bessel +czech
+lon_0=24d50 +lat_0=49d30
+lat_t=59d42'42.69689 +lat_1=78d30 +k_0=.9999
To generate Czech grid system values the flag option +czech
must be used to shift math-x to Y and math-y to X, changing
the sign to positive in Czech area. That is plus y west of
Helsinki and plus x south of Helsinki.
Another factor to resolve is the longitude used by the Czechs.
Test values of FORTRAN and C code examples us Greenwich PM
data but one example obviously must use another meridian---
perhaps the Ferro one. The above script is set for
Greenwich.
Lastly, the inverse has to be added but once we have a
good forward, this should not take as much time.
If anyone is interested in the math I would be glad to
email a pdf file---about 26k in .gz or 50+k in uncompressed
form. As far as I know, this is now the defining math
for the Krovak in English. Please ask for a copy, review
it and let me know of any deficiencies.
For hassles in using the Krovak in Grass, I suggest they
use the native math form with false eastings and northings
to get positive first quadrant values and not mess with the
code.
Lastly, I tried to make the basic projection modifiable for
general applications. Some simplifications in the cod were
made so that future mods may be required for true generality.
If I had included the total math there would have been a few
more + options to worry about.
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