Transform coordinates using nadgrids? about projnet4geoapi HOT 12 OPEN

@FObermaier I'll do a pull request.

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PROJ4 extension is not supported by ProjNet4GeoAPI at this time, I think.

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I'm hitting the same issue, in my case I need to transform GK4 to WGS84 using BETA2007.gsb gridfile. Is there any plan to implement this?
Thanks!

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I needed the same transformation from GK to ETRS89/UTM, so here's some code to test: https://github.com/wo80/NTv2

Take a look at CoordinateTransformTest.cs to see how a grid file can be used.

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Works great, thanks!
Would be nice to have it integrated into NetTopologySuite.

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@wo80, well done, do you mind us merging your project into this project?

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@FObermaier not at all.

For a more feature complete version the CoordinateTransformationFactory extension methods have to be reviewed/extended, since they were just written to work with the German coordinate systems. Other CS combinations might not work as expected (I tested NAD27 <> NAD83 and there was a clear difference to what some online converters show, see TestNAD).

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@wo80, I noticed that you are still working on it. Give us a hint when you think it is in a state for merging.
Or would you like to do it yourself?

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@wo80, just noticed that WGS84->GK4 fails with "No support for transforming between the two specified coordinate systems", can also this transformation be supported? Isn't it just a matter of extending the IF inside CreateFromCoordinateSystems method?

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Seems that adding this part in there, does the trick:

else if (sourceCS is GeographicCoordinateSystem && targetCS is ProjectedCoordinateSystem)
{
	ct = factory.CreateFromCoordinateSystems(sourceCS, targetCS);

	var list = GetCoordinateTransformationList(ct);

	// list[0] = source geographic -> geocentric
	// list[1] =        geocentric -> target projected

	// Replace the geographic transform with our grid transformation.
	list[0] = CreateCoordinateTransformation((ICoordinateTransformation)list[0], grid, inverse);
}
else if (sourceCS is ProjectedCoordinateSystem && targetCS is GeographicCoordinateSystem)
{
	ct = factory.CreateFromCoordinateSystems(sourceCS, targetCS);

	var list = GetCoordinateTransformationList(ct);

	// list[0] = source projected -> geocentric
	// list[1] =        geocentric -> target geographic

	// Replace the geographic transform with our grid transformation.
	list[1] = CreateCoordinateTransformation((ICoordinateTransformation)list[1], grid, inverse);
}

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@ondrasvoboda thanks, I'll add it to the pull request.

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cool, thanks

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