topic Re: Wrong values for Geographic Transformation in ArcObjects SDK Questions

Wrong values for Geographic Transformation

AlexanderHaberl — Mon, 08 Jul 2013 14:10:35 GMT

Hi!
I want to transform a number of points from MGI_Austria_GK_East to GCS_WGS_1984. When I do that in ArcMap (with the "Project" tool) everything works perfectly. Now I tried to do the same programmatically in C#, but the results are totally wrong. Please help and tell me, what I am doing wrong! Thanks a lot!
Here's my code:

private void btnStartTransform_Click(object sender, EventArgs e)         {             Type factoryType = Type.GetTypeFromProgID("esriGeometry.SpatialReferenceEnvironment");             System.Object obj = Activator.CreateInstance(factoryType);             ISpatialReferenceFactory2 spatialReferenceFactory2 = obj as ISpatialReferenceFactory2;              IGeoTransformation geoTransformation = spatialReferenceFactory2.CreateGeoTransformation((int)esriSRGeoTransformation3Type.esriSRGeoTransformation_MGI_To_WGS_1984_3) as IGeoTransformation;              //In Point (MGI_Austria_GK_East): -50545.72, 362614.3             //Out Point should be: (WGS1984 Longitude/Latitude in decimal degree): 15.649504022257, 48.3997325959545              double[] inPoints = new double[2];             double[] outPoints = new double[2];              inPoints[0] = -50545.72d;             inPoints[1] = 362614.3d;              geoTransformation.TransformPointsFF(esriTransformDirection.esriTransformForward, 1, ref inPoints[0], ref outPoints[0]);              //Values are: -6.2468353377012207, 89.99439100965067 ????             System.Windows.Forms.MessageBox.Show("Longitude:" + outPoints[0] + ", Latitude: " + outPoints[1]);         }

Re: Wrong values for Geographic Transformation

MelitaKennedy — Mon, 08 Jul 2013 17:15:05 GMT

Change the order of the input x and y values. In Esri-land, x = easting, y = northing and the order is x,y. If coordinates are in a geographic coordinate reference system, they're usually given in longitude,latitude order.

Melita

Re: Wrong values for Geographic Transformation

AlexanderHaberl — Mon, 08 Jul 2013 17:42:42 GMT

Thanks for your reply, I already tried to swap the coordinates, that gives me

[0] = 25.035063914873405
[1] = -89.994743157825781

in my outpoints array...

Here are the values I should get again:

//In Point (MGI_Austria_GK_East): -50545.72, 362614.3
//Out Point should be: (WGS1984 Longitude/Latitude in decimal degree): 15.649504022257, 48.3997325959545

Re: Wrong values for Geographic Transformation

MelitaKennedy — Mon, 08 Jul 2013 18:15:55 GMT

Oh, stupid me! I didn't read your post closely enough.

Is there a reason why you aren't using ProjectEx rather than TransformFF? I think it's treating the input coordinates are decimal degrees rather than unproject them, then apply the geotransformation.

Melita

Re: Wrong values for Geographic Transformation

AlexanderHaberl — Mon, 08 Jul 2013 19:55:04 GMT

Thanks a lot, it works with ProjextEx() method.