[Proj] confused from krovak

Clifford J Mugnier cjmce at lsu.edu
Fri Mar 17 09:10:03 EST 2006

The comment below regarding transformed ellipsoid height is getting quite
far from the general topic of cartography, GIS, and map projections.  When
concern is voiced over ellipsoid heights in combined datum shift and
projection transformations, the user is now deep into geodesy.

In fact, the topic is termed PHYSICAL Geodesy, and the appropriate
application of "GEOIDS" is in order.

The Bessel ellipsoid was cooked up in 1841.  The Krovak projection was
cooked up in 1922.  The Czech Republic is still referenced to the
Hermannskoegel Datum of 1871 when using the Krovak projection.  Note that
these are systems with origins from two centuries ago!  Trying to reconcile
these ancient systems with a GPS system is mostly a waste of time with
respect to ellipsoid heights.  That old datum does NOT have a geoid
associated with it.  It does not even have an old-timey astrogeodetic
deflection geoid computed muchless a geoid that could be comparable to the
EGM96 geoid.

The PROJ4 collection of cartographic and geometric utilities is not a
panacea to all problems geodetic!  If the Czech Republic is prepared to
sink several hundred million dollars into defining a geoid for its old
datum, then ellipsoid heights will make then make (more) sense to the
neophyte GIS user.  Until that happens, don't expect miracles from PROJ4.
You will need a Hermannskoegel 1871 Datum Geoid for that to happen, and
that's not going to happen.  It would be a waste of money.

I believe the Czech Republic government is working on a local national
geoid to be compatible with a new inertial datum that is associated with
the International Terrestrial Reference Frame (ITRF); a proper use of
public money.

Clifford J. Mugnier, C.P., C.M.S.
Chief of Geodesy,
Department of Civil Engineering
CEBA 3223A
Baton Rouge, LA  70803
Voice and Facsimile:  (225) 578-8536 [Academic]
Voice and Facsimile:  (225) 578-4474 [Research]

> 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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