[PROJ] Understanding dropped parameters for stere and latlong

[David Hoese]

Thanks Even and Martin,

I've never tried changing the prime meridian. I'll give that a shot.

The end goal for the user I'm talking to is to make a geotiff with 
satellite data that spans the anti-meridian but is still one contiguous 
image (no split at -180/180). I'm not sure how they are using the image 
so not sure of their limitations. I'm thinking that an old hack we have 
in our image generation software to always return lon/lat degrees for 
geographic coordinate transformations (lon/lat <-> lon/lat) instead of 
the radians that were being used is causing the issue they are seeing.

I *think* I can take it from here. Thanks for the information.

Dave

On 4/12/20 5:26 PM, Even Rouault wrote:
> On lundi 13 avril 2020 00:10:14 CEST Martin Desruisseaux wrote:
> 
>  > Why not using PRIMEM, for example like below?
> 
>  >
> 
>  > GEODCRS["WGS 84 (anti-meridian)",
> 
>  > DATUM["World Geodetic System 1984",
> 
>  > ELLIPSOID["WGS 84", 6378137, 298.257223563,
> 
>  > LENGTHUNIT["metre",1.0]]], PRIMEM["Anti-meridian", 180,
> 
>  > ANGLEUNIT["degree",0.01745329252]], CS[ellipsoidal,2],
> 
>  > AXIS["latitude",north,ORDER[1]],
> 
>  > AXIS["longitude",east,ORDER[2]],
> 
>  > ANGLEUNIT["degree",0.01745329252]]
> 
>  >
> 
>  > It should create a CRS with longitude in -180 to 180° range, but where
> 
>  > 0° is at 180° from Greenwich (I not sure if this is what you wanted).
> 
> That's a good point. If you use "+proj=longlat +pm=45", this will 
> actually set the PRIMEM[]. "+proj=longlat +pm=" and "+proj=longlat 
> +lon_0=" seem to behave quite simimarly from a quick test. The +over 
> trick however is a PROJ specific thing. If you need to serialize this, 
> there's no alternative than storing the PROJ string itself.
> 
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> 
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