Is there a way to combine Coordinate Frame transformation method and custom grid-based NTV2 method into single transformation method? Right now, in ArcGIS Desktop there is only possibility to choose either first or second method, but have anybody tried to combine these two into singular one?
Thanks in advance!
Sub twoGT() '1)Create our factory Dim pSpatRefFact As ISpatialReferenceFactory2 Set pSpatRefFact = New SpatialReferenceEnvironment Dim pGeoTrans_A As IGeoTransformation Dim pGeoTrans_B As IGeoTransformation '2)Use the factory to create our geotransformation objects Set pGeoTrans_A = _ pSpatRefFact.CreateGeoTransformation(esriSRGeoTransformation_ED1950_To_WGS1984_1) Set pGeoTrans_B = _ pSpatRefFact.CreateGeoTransformation(esriSRGeoTransformation_Belge_1972_To_WGS_1984_1) '3)Create a composite geotransformation object Dim pGeoTransComposite As ICompositeGeoTransformation Set pGeoTransComposite = New CompositeGeoTransformation '4)Add the two separate geotransformations to the composite pGeoTransComposite.Add esriTransformForward, pGeoTrans_A pGeoTransComposite.Add esriTransformReverse, pGeoTrans_B '5)Give the new transformation a name. Dim pNewGeoTrans as IGeoTransformation Set pNewGeoTrans = pGeoTransComposite pNewGeoTrans.Name = "ED_1950_To_BD_1972" End Sub
Thank you for VBA sample, it did help us. While exploring this combination of transformations, we have spotted some problems. We are trying to do transformations from Gauss-Kruger to ETRS89 using combination of Helmert transformation of 7 parameters and custom grid-based transformation. Grid has cells of 1000x1000 meters, and covers entire territory of Serbia, is based on residuals from Helmert transformation, while for gridding method was used Inverse Distance to a Power, with radius of 10000 meters. Doing such transformations, we got results that differs from results we got using other software (non-GIS) that calculates transformations: 95% of coordinates were exact, whilst 5% were wrong (not satisfying standards of our client, since coordinates must have error not larger than 10 cm). By researching all the methods we have used, we spotted that NTV2 custom grid in ArcGIS is in arc-seconds. Is it possible to have custom NTV2 grid in Cartesian coordinates rather than in arc-seconds, in ArcGIS? Also, is there a tool that can convert grid from ASCII to GSB format in ArcGIS?
Thank you in advance!