Trying to trasnform GCS_Bessel_1841 PCS_Trasnverse Mercator (central meridian 18) to WGS1984 using "Project tool" in ArcGIS 9.3. I tried to do it in several different ways, every time from the beginning.

In project dialog box under Output coordinate system I choose

a) Select predefined PCS. I choose WGS PDC. Nothing happens. b) Select predefined GCS. I choose World/WGS_1984. Nothing happens. c) Import from an existing dataset. Nothing happens. d) I go to Layers, Transformations, select "Convert from GCS_Bessel_1841 to World/WGS_1984 (from the drop down menu). I select "using New Geographic Transformation" and choose position vector with seven variables which I got from here


Nothing happens. The polygons remain the same, and the PCS is always the TM I started with.

Please help. Obvious ideas are welcome. As are a few short sentences behind the rationale of the system. I know what a PCS and GCS and datums are :) The country is Croatia.


In ArcGIS 9.3, the Project Tool doesn't support custom geographic transformations. We also hadn't added MGI 1901 yet. There is a tool, Create Custom Geographic Transformation, that allows you to create a custom geographic transformation which is saved in a .gtf file and can then be used in the Project Tool or in ArcMap. You have to be careful to match the GCS definition in the transformation with the one being used by the data.

Your description of (d) sounds like it's in ArcMap. I'm assuming that the display changes, but the original data doesn't. That's what should happen. ArcMap is creating a temporary, in-memory version. If you want to persist the data in the new coordinate system, right-click the layer in the table of contents and select data, export data. In that dialog, use the data frame's coordinate system.

Note: when you define a custom transformation, if the source and target GCS are swapped in the transformation definition that you have, make sure to change the signs on all the parameter values.

If the display doesn't change after setting the new data frame's coordinate system, I suspect something's wrong with the data's coordinate system already. The coordinate values are so out of whack with the coordinate system definition that the software can't do anything with the data. That could also occur in the Project Tool. If this is the case, please update your question with a sample coordinate pair from your data plus approximately what place it represents (or its lat/lon equivalent).

  • Correct, it is ArcMap. What happens is actually nothing - even the display doesn't change (I mean, the new layer is added, it changes colour and name, but says exactly in the same place). Also, in Layers menu after the Custom Geographic Transformation (with importing the coordinate system, because I have one shp which is correctly projected and I want to match evertyhing else with it) it still says GCS_Bessel_1841 PCS_Transverse Mercator, so nothing changes. The place is Krapina County, Croatia. It's capital, Krapina is at 15,8 and 46,1 decimal degrees. I hope I understood well what you asked. – Marin Aug 7 '13 at 9:53

So, I found what was the problem. My data was in PCS and first I had to change it to GCS. So I went to Data Frame Properties/Coordinate System and selected a GCS.

For Croatia and a big part of ex-Yu it's MGI or Bessel_1841 or Hermannskoegel. Basically it's the same thing but with different names.

So after I have my data in GCS I went to do the vector position transformation with seven parameters I found at Georepository. Worked perfectly. But thanks for your help.

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