[Proj] confused from krovak

Oscar van Vlijmen ovv at hetnet.nl
Fri Mar 17 05:00:28 EST 2006

> From: Jachym Cepicky
> Subject: [Proj] confused from krovak

> My data are stored in Krovak projection (known as S-JTSK). All the data
> are in "GIS version of Krovak", which means for the axes, that X=-y and
> Y=-x. I used patch of PJ_krovak.c from Radim Blazek's site.
> Output of cs2cs gives me expected result:
> echo "-603056 -1.16353e+006" | cs2cs +proj=krovak +ellps=bessel
> +a=6377397.1550000003 +es=0.0066743722 +f=299.1528128000
> +towgs84=570.8,85.7,462.8,4.998,1.587,5.261,3.56 +to +proj=latlong
> +datum=WGS84 +ellps=WGS84 +no_defs
> 16d32'43.318"E  49d9'55.923"N 44.706

I can confirm this:
With my krovak function (not derived from (lib)proj) and the input
x=1163530; y=603056; (note the +)
I arrive at lat, lon wrt Greenwich:
lat=49.1661377; lon=16.5466812 decimal degrees
which after datum transform with your parameters gives:
lat=49d 09m 55.9232s; lon=16d 32m 43.3178s; h=44.7065 m

> ....
> To use EPSG code seems not to be working -- Krovak is defined with
> <2065> +proj=krovak +lat_0=49.5 +lon_0=60.16666666666667
> +alpha=30.28813972222222 +k=0.9999 +x_0=0 +y_0=0 +ellps=bessel +pm=ferro
> +units=m +no_defs

In the mean time EPSG has updated the parameters (alpha for 0.1
milliarcsec), but this won't make any difference.

> and using this parameters with cs2cs gives
> echo "-603056 -1.16353e+006" | cs2cs +proj=krovak +lat_0=49.5
> +lon_0=60.16666666666667 +alpha=30.28813972222222 +k=0.9999 +x_0=0 +y_0=0
> +ellps=bessel +pm=ferro +units=m +no_defs +to +proj=latlong +datum=WGS84
> +ellps=WGS84 +no_defs
> 34d12'48.052"E  49d10'0.227"N -701.834
> which is definitely bad result

Remains to be seen. With my 'krovak' set to Ferro as prime meridian I
lat=49d 09m 58.0958s; lon=34d 12m 48.0524s
This is still on the Bessel ellipsoid!!!
For your excessive height (depth) I have no explanation. Your latitude
differs by 2" with mine, which is not very significant.
Probably this information will help you to cure the cs2cs command line?

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