[OSRS-PROJ] Horrors of --- Krovak projection

Gerald I. Evenden gerald.evenden at verizon.net
Tue Feb 25 12:37:27 EST 2003

The test scripts as they are now constructed use the Ferro PM.  To
use Greenwich PM modify the lon_0 factor to account for the offset
of Ferro from Greenwich---17d40 if I recall correctly.  The main
thing is to keep the geographic longitude coordinates correct
relative to longitude parameters such as lon_0.  How the PM option
that was installed in your PROJ works is unknown to me at this time.
If it only translates the I/O longitude then only modify the
controls in the script to indicate the PM and use Greenwich I/O.

An aside to the Ferro PM is its exact value.  The statement has
been made that the rounded 17d40 value is often used by topographers but
the true correction is 17d39'59.7354".  What do geodesists and
cadastral users employ?

The +czech flag merely puts the x-y output in the form defined
by the Czechs for their system: Y positive to the left of the
origin longitude and X positive south from the conic apex (a point
in Finland).  Without the flag the x is negative to the left of
the origin longitude and y is negative south of the cone apex.
If you need positive numbers in this mode use false eastings/

Another aside: to test the projection's inverse, the script shows
how the -o, -i binary I/O link the forward and inverse executions
so the formatter does not get in the way of transferring the
data and thus giving slight but confusing differences in the
inverse results.

On Tue, 2003-02-25 at 10:32, Frank Warmerdam wrote:
> Gerald I. Evenden wrote:
> > Per yesterday's promise the following web site contains Krovak
> > documentation, PROJ.4 C code and test script:
> > 
> > http://members.bellatlantic.net/~vze2hc4d/proj4/
> Gerald,
> I have added a link to your web site from the site at RemoteSensing.org.
> I hope to incorporate your version of the Krovak into my version though
> I am not sure when I will get to that.  I will likely remove the existing
> code and replace it with yours though I want to review how to get the
> expected results with prime meridians and also the implications of the
> +czech flag.
> Best regards,

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