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Preface: Some time ago the Czechoslovakian used the S-JTSK (Souřadnicový systém Jednotné trigonometrické sítě katastrální, lit. "Coordinate system for unified trigonometric cadastral networks") on the S-42/SK-42 Krasovski 1940 ellipsoid, through the Krovak transform. After splitting to Czechia and Slovakia in 1993, modifications were added to this system (and the Krovak transform) in order to be more accurate in each country. These are JTSK03 for Slovakia, and S-JTSK/05 for the Czech Republic now. Unfortunately, many sources and applications don't make this distinction, calling all three versions simply as "S-JTSK". It makes a lot of confusion.

Question: What EPSG should I use? I've tried all reference/coordinate systems in QGIS having JTSK or Krovak in their names but all of them were off by large. By that I mean hundreds of kilometres.

I have the following points from LPIS (Land Parcel Information System) that I try to match:

-818384.5723, -1014296.9815 (S-JTSK/05) => 50.245373328547686, 13.31661422185417 (WGS-84)

-528744.5675, -1176787.8436 (S-JTSK/05) => 49.11477804083318, 17.577094303962053 (WGS-84)

I have the conversion formulae so I can calculate the forward and reverse transform. Still, it would be nice to display the original data in GIS software.

Edit: As I was sure the Czech cadastre used CRS:2065, I've played with it in QGIS. Finally I've managed to get the points in <10 cms accuracy using EPSG:2065. I only had to remove the negative signs from the coordinates manually. One may change it in the PROJCS itself, by using PARAMETER["X_Scale",-1.0],PARAMETER["Y_Scale",-1.0].

Why not closing the question then? I still don't have a clean EPSG number that I can apply without modifications. Moreover, it uses Ferro as the prime meridian while my formulae are Greenwich-based. (The Remarks section of the EPSG:2065 page gives some insight on its reasons.)

The EPSG Geodetic Parameter Registry gives a nice list for the "S-JTSK/05" search - and big thumbs up for them as they distinguish the geodetic CRS, the projected CRS, the coordinate transform, etc. One can even check which EPSG is northing-easting, and which one is southing-westing.

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  • I think, if you have the conversion formulae, you can define your own custom CRS in QGIS. – Stefan Jun 17 '20 at 13:10
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The first entry in DuckDuckGo for "S-JTSK/05" leads to https://epsg.io/5228

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  • epsg.io/?q=S-JTSK%2F05 will give all of the possibilities – Ian Turton Jun 17 '20 at 13:18
  • I myself use DDG, and of course I've met this EPSG. However, the shapes from LPIS (e.g, the official land cadastre) are quite off using 5228. – Yogurt Jun 17 '20 at 13:40
  • I didn't want embarrass you. There was a high chance that you had used a search engine. It was not clear from your question what you had tried. :) – Stefan Jun 17 '20 at 15:23

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