[Proj] Krovak again
Mikael.Rittri at carmenta.com
Wed Aug 17 05:40:52 EST 2011
> 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.
There are basically two families of Czech-and-Slovakian
* 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.
> 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
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
EPSG:5224, 5225, 5515 and 5516.
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:
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.
The national Inspire Czech Geoportal site shows negative values increasing to the south and west in the lower left corner on mouse movement.
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.
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