[PROJ] Pipeline from "Local" projection to EPSG:4326

[Māris Nartišs]

Hello Even,

2020-09-25 18:42 GMT+03:00, Even Rouault <even.rouault at spatialys.com>:
> On vendredi 25 septembre 2020 15:22:40 CEST Māris Nartišs wrote:
>
> See discussion thread
> https://lists.osgeo.org/pipermail/proj/2020-September/thread.html#9818
> in case you missed it

Thanks, I already seen that.

> Which must be as close as you wish
>
> echo "22000 77000 0" | cct -d 8 +proj=pipeline +step +inv +proj=ortho
> +lat_0=41.329238
> +lon_0=69.295403 +x_0=24547.608 +y_0=76540.608 +ellps=krass +step +proj=push
> +v_3
> +step +proj=cart +ellps=krass +step +proj=helmert +x=25 +y=-141 +z=-78.5
> +rx=0 +ry=-0.35
> +rz=-0.736 +s=0 +convention=coordinate_frame +step +inv +proj=cart
> +ellps=WGS84 +step
> +proj=pop +v_3 +step +proj=unitconvert +xy_in=rad +xy_out=deg +step
> +proj=axisswap
> +order=2,1

I was so close :-(

> This isn't exactly the coordinates you mention, probably due to the issue of
> PROJ ortho not
> implementing the ellipsoidal formulation whereas ESRI Local does.

Most likely. If I replaced +proj=ortho with +proj=tmerc, it would give
exact coordinates I mentioned.

>
>> 2) how to make it "default" pipeline for the source CRS for all proj
>> utilizing tools (ogr2ogr, QGIS etc.)?
>
> This is a tricky aspect. The current philosophy is that you either trust
> PROJ automated way to
> select the right pipeline (PROJ's cs2cs, GDAL utilities with no explicit
> pipeline, etc.), or you
> choose it yourself (with PROJ's cct utility, GDAL's ogr2ogr/gdalwarp -ct
> switch, QGIS UI datum
> change preference dialog box)
> You could manage to change PROJ's default by tweeking PROJ's db. Either by
> adding a new
> record to it with a better accuracy than the ones present, or modifying the
> accuracy of an
> existing transform to be better than the best one presented by PROJ

Thanks for detailed explanation.
Māris.