Georeference CAD Data

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10-17-2013 08:31 AM
LaurenWoodruff
New Contributor
I need some advice on georeferencing some CAD data that I have imported in a geodatabase. The CAD data is a network of stormwater drainage for a small city. I have another dataset of points and lines that were created using aerial photos as the source. The features from the aerial photos and the CAD data do not quite match up. I am not quite sure the best way to go about getting the most accurate locations for the features. Should I use the spatial adjustment tool to adjust the CAD data based on the location of the aerial photo data? If so, what kind of transformation should I use? How should I determine where to set my displacement links so that the features will be accurate?

Thanks
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9 Replies
TOMKONG
Occasional Contributor II
I need some advice on georeferencing some CAD data that I have imported in a geodatabase. The CAD data is a network of stormwater drainage for a small city. I have another dataset of points and lines that were created using aerial photos as the source. The features from the aerial photos and the CAD data do not quite match up. I am not quite sure the best way to go about getting the most accurate locations for the features. Should I use the spatial adjustment tool to adjust the CAD data based on the location of the aerial photo data? If so, what kind of transformation should I use? How should I determine where to set my displacement links so that the features will be accurate?

Thanks


Your CAD data imported from another geodatabase & aerial photos should have the spatial reference already, you can't georeference them again.


If your CAD data is the As-Built or Planned map, you should edit eavery incorrect features based on the image (you can check the image accurace first according to some control points).
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RobertBorchert
Frequent Contributor III
Do you have AutoCAD?



It is very quick and easy to georeference in CAD

I won't reply with my long answer as it won't matter if you don't have CAD
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collindegueurce
New Contributor III

I have CAD and a similar issue. Would love to read your reply!

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RobertBorchert
Frequent Contributor III

First find specific places in your CAD drawing that can be referenced to a location in the world.  For most of my CAD georeferencing I have been fortunate to have section corners or QQD. Often when referencing CAD Plat drawings there will be a reference point and distances.  Sometimes in larger drawings it helps a lot to put a POINT on those locations and give it a large obvious symbol.  It would be BEST if you can location TWO reference points as far apart as possible.

IF you cannot determine two points but you have a known distance, say along the edge of a series of parcels.  Calculate that length from the reference point to the end.

Generally speaking some place you can determine the exact location in ArcGIS

For this example I will use section polygons.

I go into ArcGIS and open the section polygons.  I select those that are in the area I am locating.  Export them as a shape file.  Import the shape file into a NEW autocad drawing.  Be sure to import projection data.   Import the polygons as closed polylines.  Once they are in CAD lock the layer.

Add your drawing to be georeferenced as a block. Z enter E (zoom extents).  Make sure all of your drawing layers are visible and unlocked (other than the reference sections).  Select all of the drawing elements and drag them close to your reference sections.

Z E again.  Now wiht all your elements still selected use MOVE, select one of your reference points and move it to the reference point on your reference sections.  IF you feel you need to rotate the drawing and your cad drawing has a East West or North South line then put in a construction line and rotate your drawing using the ROTATE command.

Go back to your section reference point and then use the SCALE command to rescale the CAD drawing between the two reference points.

save your drawing. You should now be able to open it in ArcGIS.  In CATALOG  you can assign it the projectoin from  the shape file.

I once had to convert a 5 county wide electric distribution system that the original CAD technician had thought they were doing to proper size when in fact they had used millimeters instead of feet.  They also made the mistake of assuming all section lines were all norht south east west

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collindegueurce
New Contributor III

Thank you very much for your answer. That helped me out a lot!

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DonKuehne
Occasional Contributor III

If you would like to permanently modify your  AutoCAD drawings to line up with things in the real world based on ArcGIS web services then the AFA_GEOALIGN tool and workflow presented in the ArcGIS for AutoCAD bonus tools were created to do just that.  The tools work with ArcGIS for AutoCAD 350 that you can freely download here:  There are also videos (here) that give you and overview of the tools in action to see if the might work for you.   I think the video uses a map service, but using a feature service would provide more accurate objects to snap to.

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collindegueurce
New Contributor III

I will try that. Thanks!

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larryzhang
Regular Contributor

Generally, it is always challenging to seamlessly integrate CAD into GIS, because the gaps /precisions between CAD and GIS still exist, in particular, when working on 3D integration from Microstation (in that 3D CAD models are usually huge, very detailed and complicated to 3D GIS…)

However, on aspects of 2D CAD integration into ArcGIS, it can mostly be handled without big difficulty. For example, ESRI provides some solutions to georeference/ geo-link CAD drawings through using auxiliary file with GCPs in ArcGIS. Just keep in mind, those CAD drawing are not really geo-corrected ‘permanently’ ...

Please refer to the Doc at http://resources.arcgis.com/en/help/main/10.2/#/About_georeferencing_CAD_datasets/001000000010000000...

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collindegueurce
New Contributor III

Thanks for the reply...very useful doc!

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