[Proj] Krovak again

[Mikael Rittri]

Hello Irwin.

> What is EPSG 102067?  It's not in the EPSG database. 

True, there is no such thing as EPSG:102067. Someone must
have meant ESRI:102067, which is called Krovak East North.

http://spatialreference.org/ref/esri/102067/

There are basically two families of Czech-and-Slovakian
Krovak instances.  

  * In the "classical" ones, for example S-JTSK / Krovak (EPSG:5513), 
    the first axis (X) goes south, and the second axis Y goes west.

  * In the "GIS" variants, for example ESRI:102067, the
    axes go east and north, which is necessary in many 
    GIS systems. They should have the phrase "East North"
    in their name. 

A property they all share is that the grid origin 
(where both projected coordinates are zero) is at the 
oblique cone apex between Helsinki and Tallinn,
northeast of Czech-and-Slovakia.    

This means that in the "classical" (South West) variants,
all projected coordinates are positive in Czech-and-Slovakia,
but in the GIS variants, they are negative there. 

You wrote:

> The national Inspire Czech Geoportal site shows 
> negative values increasing to the south and west

I don't understand that. So I hope that when you say 
"negative values increasing" to the south and west, 
you mean that the values become _more_ negative, 
that is: the values decrease, but their absolute 
values increase, towards south and west.

It took many years for EPSG to add GIS-Krovak variants,
so the ESRI codes for some Krovak variants have become 
popular: 

   ESRI:102065, S-JTSK Krovak
   ESRI:102066, S-JTSK Ferro Krovak East North
   ESRI:102067, S-JTSK Krovak East North

These are equivalent, as far as I know, to the recent EPSG entries

   EPSG:5513, S-JTSK / Krovak
   EPSG:5221, S-JTSK (Ferro) / Krovak East North
   EPSG:5514, S-JTSK / Krovak East North

respectively. Then, you have also the oldest variant

   EPSG:2065, S-JTSK (Ferro) / Krovak.

Furthermore, Czech authorities have introduced a modified 
version of the S-JTSK datum, which is called S-JTSK/05. 
With this modified datum, you must use a "Modified Krovak" 
projection, which somehow compensates for distortions in 
the datum realisation (I don't understand the design or purpose,
but I believe the modifications do not change coordinates 
more than about 1 meter). There are four EPSG entries based 
on S-JTSK/05: 
    EPSG:5224, 5225, 5515 and 5516. 

Best Regards,

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com

-----Original Message-----
From: proj-bounces at lists.maptools.org [mailto:proj-bounces at lists.maptools.org] On Behalf Of Irwin Scollar
Sent: den 17 augusti 2011 10:44
To: proj at lists.maptools.org
Subject: [Proj] Krovak again

The Czech GeoPortal site:

http://geoportal.cuzk.cz  (COSMC)

shows positive coordinates (Krovak) increasing to the south and the west when the mouse cursor is moved over a map or an orthophoto.

A map area centered on Prague on the COSMC site automatically shows the bounding box coordinates as negative numbers in the search field of the web browser.

http://geoportal.cuzk.cz/cuzk_wmsklient/Default.aspx?CRS=EPSG:102067&variant=ortofoto&BBOX=-826324.245856,-1224934.494271,-713435.417927,-1140267.873324

The national Inspire Czech Geoportal site shows negative values increasing to the south and west in the lower left corner on mouse movement.

http://geoportal.gov.cz/web/guest

Which Krovak variant shown in OGP Publication 373-7.2 p 25ff is involved here or is this yet another variant?

What is EPSG 102067?  It's not in the EPSG database.

Irwin Scollar

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