Anyway a proper pipeline I use for years is:
+proj=pipeline +step +inv +proj=krovak +lat_0=49.5
+lon_0=24.8333333333333 +alpha=30.2881397527778 +k=0.9999 +x_0=0
+y_0=0 +ellps=bessel +step +inv +proj=hgridshift
+grids=Slovakia_JTSK03_to_JTSK.gsb +step +proj=krovak +lat_0=49.5
+lon_0=24.8333333333333 +alpha=30.2881397527778 +k=0.9999 +x_0=0
+y_0=0 +ellps=bessel +step +inv +proj=krovak +lat_0=49.5
+lon_0=24.8333333333333 +alpha=30.2881397527778 +k=0.9999 +x_0=0
+y_0=0 +ellps=bessel +step +proj=push +v_3 +step +proj=cart
+ellps=bessel +step +proj=helmert +x=485.021 +y=169.465 +z=483.839
+rx=-7.786342 +ry=-4.397554 +rz=-4.102655 +s=0
+convention=coordinate_frame +step +inv +proj=cart +ellps=WGS84 +step
+proj=pop +v_3 +step +proj=webmerc +lat_0=0 +lon_0=0 +x_0=0 +y_0=0
+ellps=WGS84
It is the official pipeline provided by our national cartography
office, together with Slovakia_JTSK03_to_JTSK.gsb file. Without this
pipeline the offset varies up to more than 10 meters. With the
pipeline the transformed geotata matches that from state office's WMS 🙂
It makes slightly more sense, but still seems dubious to me
The part "+step +inv +proj=krovak +lat_0=49.5 +lon_0=24.8333333333333
+alpha=30.2881397527778 +k=0.9999 +x_0=0 +y_0=0 +ellps=bessel +step +inv
+proj=hgridshift +grids=Slovakia_JTSK03_to_JTSK.gsb +step +proj=krovak
+lat_0=49.5 +lon_0=24.8333333333333 +alpha=30.2881397527778 +k=0.9999
+x_0=0 +y_0=0 +ellps=bessel" is what you would want to apply to go
*from* "S-JTSK / Krovak East North" to "S-JTSK [JTSK03] / Krovak East
North"
and then the second part uses the expected Helmert tranformation from
"S-JTSK [JTSK03] / Krovak East North" to WGS 84, so this pipeline is to
go from "S-JTSK / Krovak East North" to WebMercator WGS 84.
Perhaps your dataset is mislabelled as being in "S-JTSK [JTSK03] /
Krovak East North" whereas it is in "S-JTSK / Krovak East North" ?
--
http://www.spatialys.com
My software is free, but my time generally not.
Butcher of all kinds of standards, open or closed formats. At the end, this is
just about bytes.
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