[Proj] Pipeline +init files, inverse

[Thomas Knudsen]

Steve,

Essentially (leaving out the double inversions), your "case 2" does this:

<case2>
proj=pipeline
step proj=tmerc lat_0=49 lon_0=-2 k=0.9996012717
                          x_0=400000 y_0=-100000 ellps=airy
step proj=vgridshift grids=OSGM15_GTX_OSGBtoGRS80.gtx
step proj=hgridshift grids=OSTN15_NTv2_OSGBtoETRS.gsb inv

But your grid is given in geographic coordinates, not transverse mercator
(cf. gdalinfo output [1] below), so starting your pipeline going from geo
to transverse mercator takes you way outside the grid coverage.

So start doing the gridshifts, then do the projection. When doing that, you
get this:

$ echo -3 55 100 | cct -t0 +init=OSGBtrans:case2
  335948.6065    567743.2288       47.5270        0.0000

/Thomas




[1]  gdalinfo OSGM15_GTX_OSGBtoGRS80.gtx

Driver: GTX/NOAA Vertical Datum .GTX
Files: OSGM15_GTX_OSGBtoGRS80.gtx
Size is 661, 1441
Coordinate System is:
GEOGCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.257223563,
            AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0,
        AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.0174532925199433,
        AUTHORITY["EPSG","9122"]],
    AUTHORITY["EPSG","4326"]]
Origin = (-9.008333333333329,61.004166666666627)
Pixel Size = (0.016666666666667,-0.008333333333333)
Corner Coordinates:
Upper Left  (  -9.0083333,  61.0041667) (  9d 0'30.00"W, 61d 0'15.00"N)
Lower Left  (  -9.0083333,  48.9958333) (  9d 0'30.00"W, 48d59'45.00"N)
Upper Right (   2.0083333,  61.0041667) (  2d 0'30.00"E, 61d 0'15.00"N)
Lower Right (   2.0083333,  48.9958333) (  2d 0'30.00"E, 48d59'45.00"N)
Center      (  -3.5000000,  55.0000000) (  3d30' 0.00"W, 55d 0' 0.00"N)
Band 1 Block=661x1 Type=Float32, ColorInterp=Undefined
  NoData Value=-88.8888000000000034





2018-02-23 8:46 GMT+01:00 stevejking <stevejking at talktalk.net>:

> Kristian,
> Thanks for the reply, I'll take a look at the link.
>
> For the moment, I've added the missing +step to case 3, and it now works :)
> I also removed the command line -t0's which I had in error put in the init
> file.
>
> Unfortunately case 2 is still giving the error. I even tried removing the
> breakline \'s.
>
> Will look more when time allows.
>
> ...
>
> Steve
>
>
>
> --
> Sent from: http://osgeo-org.1560.x6.nabble.com/PROJ-4-f3840930.html
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