Definitions for projected map coordinate systems which are in use in Czech Republic.
This definitions are recommended for use in MapTiler to correctly warp existing raster maps.
Click on the name of the projection to see the details:
FAQ - Frequently answered questions:
Can I use this definition in another software as well?
The definitions are also usable for other open-source GIS utilities and systems and for automatic transformation of coordinates with tools based on Proj.4. More info at: Open-source tools for map coordinate transformation.
Why can I not use EPSG codes for Czech Republic directly like I do for other countries?
Because the same code is used for both Czech Republic and Slovakia, and for each country EPSG database contains diferent suggested transformation. We can't claim EPSG code for Czech Republic when it is shared with Slovaks as well (and they use different transformation). The original idea is that cartographer choose the correct transformation himself, and in case higher quality transformation is needed he calculates his unique 7 parameters transformation from the official ground control points database of the country. So now we have several different definitions which are used for the same coordinate system.
Is there a way out of this situation at least for S-JTSK?
Cleanest possible solution for S-JTSK seems to be the usage of the grid shift file for conversion between Bessel ellipsoid [EPSG:7004] and WGS84 ellipsoid [EPSG:7030] eliminating local distortions - caused by the age of S-JTSK (history goes back to nineteen century to Austro-Hungarian empire).
Such grid should cover area of both Czech and Slovak Republic. It would eliminate the need for local-only transformations and definitively solve the transformation ambiguity for Czechoslovak S-JTSK datum. BTW there are two datums, one with Ferro meridian EPSG:4818 and second with Greenwich EPSG:4156 for this area.
Question is what precession should be choosen for this grid, high density grid (like we generated right now for area of Czech republic) is a bit slowing the transformation process, but has average error under 3cm. The original official transformations for S-JTSK system had accuracy around 60 cm.
Where can I read more about historical backgrunds of S-JTSK?
Very nice summarization is in the article of Clifford J. Mugnier, written with assistence of Bohuslav Veverka from CVUT: http://www.asprs.org/resources/grids/01-2000-czech.pdf
What would be best and clean solution?
Of course ideal solution would be to for the Czech Republic a new system (proposed S-JTSK05), without local distortions and easily tranformable with 7-parameters Helmert equations to the modern global systems like ETRS89/WGS84. Such step is problematic and it should be done by official Czech authorities - probably VUGTK/CUZK.