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Coordinates Transformation Issue

Question asked by nikolaev_d on Nov 14, 2011
Latest reply on Nov 14, 2011 by geonetadmin
Hi ESRI and all,

I am not sure if this is a proper forum but...

I think I have an important question to ask and I am sure that sharing this information will be a great benefit to everyone.

I have discovered a huge spatial difference in results when reprojecting data (project command) using different transformation methods available from the standard ESRI transformation list.

This is what I have done in ArcGIS10.

I have generated a point, which is located in Papua New Guinea using GDA94 MGA Zone56 coordinate system.

I have projected original point to AGD66 Zone56 using NTv2 transformation and my output point is shifted only about 1m from the original location, which is a bit suspicious as I know that the difference between AGD66 and GDA94 in Papua New Guinea should be about 180m-200m.

Also I have projected the original point to AGD66 Zone56 using

AGD_1966_To_GDA_1994
AGD_1966_To_GDA_1994_2
AGD_1966_To_GDA_1994_3
AGD_1966_To_GDA_1994_4

And all my results are significantly spatially distributed (far away from each other). For instance the difference between AGD_1966_To_GDA_1994_2 and AGD_1966_To_GDA_1994_3
transformation results is about 17 metres!

Is anybody out there can explain me what is going wrong with my transformations? I am aware that all transformations are supposed to produce slightly different results but 17m... I think it is too much.

I have attached an illustration for a better understanding of this issue and the original point as a shapefile.

Thanks
D

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