[gdal-dev] Re: C# Nad27 to WGS 84

[Tomas R]

I have no luck

Downloaded compiled package form http://vbkto.dyndns.org:1280/sdk/ 
(MSVC2008 (Win32) -stable, v 1500).

I set the path as described before, that is:

nadPath = 
Path.Combine(Path.GetDirectoryName(this.GetType().Assembly.Location), 
@"Gdalbin\Nad");
Environment.SetEnvironmentVariable("PROJ_LIB", nadPath);

If I check the environment variable it is set. But proj.dll perhaps do 
not share the environment variables with the C#-project? Must it perhaps 
be set globally?

I also try setting a GDAL setting with same arguments:

OSGeo.GDAL.Gdal.SetConfigOption("PROJ_LIB", nadPath);

and also that one checks out OK afterwards, that is, the setting exists 
in Gdal.

The result of the code is the same with my first version, with an 
unknown version of proj.dll. That is just de given values back. (no 
matter what target projection I use). No exception thrown as with the 
latest version of Proj4 from their website.

And the, the same as before:
            SpatialReference spatNad27 = new SpatialReference("");
            spatNad27.SetWellKnownGeogCS("Nad27");
            SpatialReference spatNad83 = new SpatialReference("");
            spatNad83.SetWellKnownGeogCS("WGS84");
            CoordinateTransformation trans = new 
CoordinateTransformation(spatNad27, spatNad83);
            double[] p = new double[3];
            trans.TransformPoint(p, -117, 30, 0);
            this.textBox1.Text = p[0] + ", " + p[1] + ", " + p[2];


and the result in the textbox is
-117
30.0000000008175
2.61394307017326E-05
which is the same result  as I get if I remove the path setting or 
remove all of Projs data files. Something is amiss.

Gdal-test env. Unsure how to set up. Should not the code above be enough?
A friend did a test in Python and he could do the transform, but that is 
no big help for me.

Any ideas what I miss or what I should test?

/Tomas
Frank Warmerdam skrev:
> Tomas R wrote:
>> Hi again,
>>
>> New problems arises as the world of Gdal is quite complex to grasp.
>>
>> Have understood that the transformation of coordinates from Nad 27 
>> datum to WGS 84 requires some look up tables to be done correctly, 
>> tables that differ with the are the Nad 27 is valid in.
>>
>> Simple question is, how to set up a general solution in C# that uses 
>> these shift tables.
>> I have in code a simple test:
>>           SpatialReference spatNad27 = new SpatialReference("");
>>            spatNad27.SetWellKnownGeogCS("Nad27");
>>            SpatialReference spatNad83 = new SpatialReference("");
>>            spatNad83.SetWellKnownGeogCS("Nad83");
>>                      CoordinateTransformation trans = new 
>> CoordinateTransformation(spatNad27, spatNad83);
>>            double[] p = new double[3];
>>            trans.TransformPoint(p, -117, 30, 0);
>>
>> that gives back
>> -117, 30,0000000008175
>> which I believe is not correct ( see http://proj.maptools.org/faq.html )
>>
>> I have Proj4.dll, I have set an environment path to PROJ_LIB where 
>> the nad shift tables should exist. Must I do something else in the 
>> setup or is the call to the transform different? or have I done 
>> correctly but misinterpreted the results?
>>
>> What I in reality is interested is transforming whatever coordinate 
>> in whatever projection/datum to and from WGS84 without any extra 
>> hassle fast and easy via the C# interface. That should not be to 
>> hard? Or?
>
> Tomas,
>
> If I test with the testepsg program (using GDAL services) with
> CPL_DEBUG and PROJ_DEBUG defined ON I get the following output.
>
> warmerda at gdal64[264]% setenv PROJ_DEBUG
> warmerda at gdal64[265]% testepsg -t NAD27 NAD83 -117 30
> OGRCT: Source: +proj=longlat +ellps=clrk66 +datum=NAD27 +no_defs
> OGRCT: Target: +proj=longlat +ellps=GRS80 +datum=NAD83 +no_defs
> pj_open_lib(conus): call 
> fopen(/wrk/home/warmerda/bld/share/proj/conus) - succeeded
> Ctable Conterminous United States 273x121: LL=(-131,20) UR=(-63,50)
> pj_open_lib(alaska): call 
> fopen(/wrk/home/warmerda/bld/share/proj/alaska) - succeeded
> Ctable Alaska 529x249: LL=(-194,46) UR=(-128,77)
> pj_open_lib(ntv2_0.gsb): call 
> fopen(/wrk/home/warmerda/bld/share/proj/ntv2_0.gsb) - failed
> pj_open_lib(ntv1_can.dat): call 
> fopen(/wrk/home/warmerda/bld/share/proj/ntv1_can.dat) - succeeded
> NTv1 393x177: LL=(-142,40) UR=(-44,84)
> pj_open_lib(conus): call 
> fopen(/wrk/home/warmerda/bld/share/proj/conus) - succeeded
> pj_apply_gridshift(): used Conterminous United States
> (-117.000000,30.000000,0.000000) -> (-117.000806,30.000113,0.000026)
>
> I don't know if it is practical for you to enable debugging and see
> stderr output, but if you can it might help you deduce what is
> or is not working.
>
> It *sounds* like you have done what is necessary, but it is hard
> for me to know if you have made some mistake, such as preprocessing
> the grid shift file into binary form.
>
> Best regards,