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I received a DGN file, I believe created in Bentley 8, and there is a bit of a misalignment problem. The dgn, when overlain on a Bing Maps aerial or NAIP image, shows up about 20 m or so off. I'm set up in NAD83 State Plane 1601 Kentucky North and using ArcGIS 10.2.1 for Desktop.

It's important that these line up fairly close because this dgn will be used to create a regulatory boundary for field surveys.

So my question is, are the aerials correct and the DGN is just slightly off or vice versa? I assume the DGN is just slightly off. My initial inclination was to align the buildings in the dgn with the buildings in the aerial photograph and go from there. However, I started getting a little nervous that maybe that would end up putting one of the field workers off the mark.

Any suggestions?

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  • Is it possible to contact the source of the DGN to confirm that the data is, in fact, supposed to be in NAD83 State Plane 1601 Kentucky North? – phloem Oct 14 '14 at 22:49
  • It has been confirmed that the projection is correct. – Robert Oct 14 '14 at 23:02
  • There will be positional error in both the DGN and Bing/NAIP. A quick search tells me Bing is generally accurate to within 5-10m, so I wouldn't count on it being more accurate than that. Your source may be able to tell you the accuracy of their dataset, which will depend largely on the instrument (e.g. GPS, survey) or digitizing scale used to create the data. Both sources of error will contribute to data not overlaying. If you need highly accurate data, you need highly accurate methods (surveys, expensive equipment, ground control, etc.). – phloem Oct 14 '14 at 23:16
  • Alright, well then I'll have to roll with what I've got until I can get an answer out of them. Thanks phloem. – Robert Oct 14 '14 at 23:34
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The first step is ensure which data have the proper information, for this matter I would try to get the coordinates from other resources (google maps, OSM, geographic services in your country),if you can identify a geodesic vertex will much better. When you compare with your data you can identify the wrong information. In case of your DGN file have the problem, the better way to fix it is transform your DGN information in shapefile and use the Spatial Adjustment tool to relocate your data (use Bing Maps aerial or NAIP image as per reference)

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As mentioned in the comment, a possible problem is the precision of your dataset, which could eplain that the data do not align. However, 20 m seems to be quite large especially in Kentucky where I would expect bing map to be at least below 5 m.

The more likely issue is the absence of transformation between WGS 84 and NAD83 when you use "on the fly" projection in ArcGIS. Go to the properties of your data frame > coordinate system > transformation and select a transform between WGS84 and NAD 83.

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