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matching coordinate systems of all my data (transforming, projecting)

My data uses the GCS_Bessel_1841 coordinate system. Would there be any inaccuracies if i would transform it to DHDN 3-Degree Gauss Zone 3? Or should i rather match all my other data to the DEMs coordinate system?

How would i do that?

  • Unfortunatelly, there seems to be no transformation method for this specific transformation from Bessel_1841 to GK3 available... At least ArcGIS does not suggest any. – chris3o12 Oct 21 '14 at 14:58
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You would only use a datum transformation if you wanted to transform your data based on Bessel to another model like WGS84/ETRS89. If all your data has a common (Bessel) base to don't need to do this.

When the data frame in ArcMap has data with several different datum(s), a warning should pop up. Get to the dataframe properties page, coordinate system tab. Click the button "Transformations". The available ones for the geographic extent you are looking at should pop up. There is a Ntv2 transform for Germany available, plus numerous others. The epsg dataset states that this Ntv2 transform is good to 1m.

  • Thanks for your answer. Unfortunatelly, there seems to be no transformation method for this specific transformation from Bessel_1841 to GK3 available... At least ArcGIS does not suggest any. – chris3o12 Oct 21 '14 at 14:57
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As long as you stay on the bessel ellipsoid, your data is pretty accurate after reprojecting to Gauss-Krüger.

You might run into datum shifts if you add WGS84 (or ETRS89) based data. There is a bunch of valid datum shifts between bessel and WGS84, depending on the part of Germany you work on.

Most accurate will be using a NTV2 datum shift grid, but this is a bit complicated in QGIS. And, to confuse more, there is a Russian definition for Bessel 1841 too. I don't know if that was used in Eastern Germany at some time.

  • Thanks for your answer! I forgot to mention that I'm working with ArcGIS and I'm located in the southwestern part of Germany. So your advice would be to use a NTV2 datum shift grid? How would I do that in ArcGIS? Sorry, I'm quite a beginner with GIS... – chris3o12 Oct 17 '14 at 7:42
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    I don't have access to Arcgis. You can add an arcgis tag to your question to declare the software you use. – AndreJ Oct 17 '14 at 8:07
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Coord sys tab ArcMap 10.2.2 Pic 1 Pic 3 Available transformations

ArcMap tells me that DHDN Gauss Zone 3 is also Bessel based (the Deutsches Hauptdreiecksnetz datum). So no trandformation is required. If you do want to transform your data to a WGS84 base, then there are a stack of transformations available. Including Ntv2 method.

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