[Proj] Krovak again
Mikael Rittri
Mikael.Rittri at carmenta.com
Wed Aug 17 05:40:52 EST 2011
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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