[PROJ] Units in a derived system

[Even Rouault]

Javier,

I have had a bit of hesitation if the current behaviour was a feature or 
a bug, and opted for the later while investigating what happened: the 
axis unit and order of the source CRS (projected CRS) were well taken 
into account to "normalize" to metre, easting/northing order before 
applying the user provided PROJ string, but the axis unit and order of 
the target CRS (derived projected CRS) were ignored.

I've addressed this per https://github.com/OSGeo/PROJ/pull/3281 . It 
might potentially break people that have compensated for that, but I 
feel it is such a marginal use case that fixing it is the best thing.

Note however that you must adjust your PROJ string: xoff must be 
expressed in meters. So you should change xoff to 65.6166666666667. Or 
do like I did in the test I added, that is convert xy from m (as I said 
above, PROJ normalizes to (resp. from) metre, easting/northing  each 
step before (resp. after) applying the user PROJ string) to us-ft, then 
apply the affine with xoff=20, and finally convert back from us-ft to xy.

Even


Le 03/08/2022 à 19:52, Javier Jimenez Shaw a écrit :
> Hi
>
> I am trying to make a derived projected CRS... in feet.
> The conversion method is a "PROJ-based operation method" with an 
> affine transformation (simplified here with just xoff of 20 feet).
> https://proj.org/operations/transformations/affine.html
>
> The derived system is something like this (my data is 3D, but in 2D is 
> also reproduced):
>
> $ cat derived.wkt
>
> DERIVEDPROJCRS["Custom Site Calibrated CRS",
>     BASEPROJCRS["NAD83(2011) / Mississippi East (ftUS)",
>         BASEGEOGCRS["NAD83(2011)",
>             DATUM["NAD83 (National Spatial Reference System 2011)",
>                 ELLIPSOID["GRS 1980",6378137,298.257222101,
>                     LENGTHUNIT["metre",1]]],
>             PRIMEM["Greenwich",0,
>                 ANGLEUNIT["degree",0.0174532925199433]]],
>         CONVERSION["SPCS83 Mississippi East zone (US Survey feet)",
>             METHOD["Transverse Mercator",
>                 ID["EPSG",9807]],
>             PARAMETER["Latitude of natural origin",29.5,
>                 ANGLEUNIT["degree",0.0174532925199433],
>                 ID["EPSG",8801]],
>             PARAMETER["Longitude of natural origin",-88.8333333333333,
>                 ANGLEUNIT["degree",0.0174532925199433],
>                 ID["EPSG",8802]],
>             PARAMETER["Scale factor at natural origin",0.99995,
>                 SCALEUNIT["unity",1],
>                 ID["EPSG",8805]],
>             PARAMETER["False easting",984250,
>                 LENGTHUNIT["US survey foot",0.304800609601219],
>                 ID["EPSG",8806]],
>             PARAMETER["False northing",0,
>                 LENGTHUNIT["US survey foot",0.304800609601219],
>                 ID["EPSG",8807]]]],
>     DERIVINGCONVERSION["Affine transformation as PROJ-based",
>         METHOD["PROJ-based operation method: +proj=pipeline +step 
> +proj=affine +xoff=20"]],
>     CS[Cartesian,2],
>         AXIS["easting (X)",east,
>             ORDER[1],
>             LENGTHUNIT["US survey foot",0.304800609601219]],
>         AXIS["northing (Y)",north,
>             ORDER[2],
>             LENGTHUNIT["US survey foot",0.304800609601219]],
>     REMARK["EPSG:6507 with 20 feet offset"]]
>
> But the output I get seems to be in meters (I deduced that running 
> with PROJ_DEBUG=3) It is kind of ignoring the CS.
> $ echo 29 -88 0 | cs2cs EPSG:6318 EPSG:6507
> 1250642.38 -180875.29 0.00
> $ echo 29 -88 0 | cs2cs EPSG:6318 "$(cat derived.wkt)"
> 381216.56 -55130.90 0.00
>
> If I concatenate the pipeline with cct, I get the result I was 
> expecting (20 feet more in the x):
> $ echo 29 -88 0 | cs2cs EPSG:6318 EPSG:6507 | cct +proj=pipeline +step 
> +proj=affine +xoff=20
> 1250662.3800   -180875.2900        0.0000
>
> Is that expected? Am I doing anything wrong?
>
> Thanks.
> .___ ._ ..._ .. . ._. .___ .. __ . _. . __..  ... .... ._ .__
> Entre dos pensamientos racionales
> hay infinitos pensamientos irracionales.
>
>
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