topic Re: Beginner Problem Projecting CAD data in Data Management Questions

Beginner Problem Projecting CAD data

AletheiaBouknight — Fri, 01 Mar 2013 17:03:06 GMT

Hi Everyone!

I apologize in advance; I am new to GIS.

I have a CAD drawing of an archaeological site that was made using assumed coordinates using total station data. Therefore, there is only one point on the map, set at a northing of 500m and an easting of 500m, that I actually know where is corresponds to in the real world (I have the real world location in UTM coordinates of the single point). I need to project this onto a topographic basemap of the area. I have tried using the georeferencing tool with little success. Do I georeference it before turning it into a shapefile? How do I even georeference this with just one point? Any advice as to how to do this would be greatly appreciated.

Thank you very much for your time! I have been banging my head against the wall for a couple days now....

Re: Beginner Problem Projecting CAD data

KarlWilson — Tue, 05 Mar 2013 06:07:12 GMT

To reference your (vector) CAD data you would need to load it into GIS first as shapefiles or feature classes. Then you would use the "Spatial Adjustment" tools in an ArcGIS Desktop edit session to reference this vector data to your basemap.

You would need more than one surveyed control point though, otherwise all your data could rotate freely about that point. I suggest surveying a good spread of additional control points if you can, for the best accuracy.

Alternatively pick easy to identify features that are both in your CAD data and on the basemap so that you can tie them together. You should be able to work out the UTM coordinates of your chosen CAD features based on the offset in x,y from your surveyed position. With this approach you are limited somewhat by the accuracy of your basemap.

Some useful links:
http://www.aubreyrhea.net/gis/index.php/2009/11/georeferencing-for-vectors-overview-of-spatial-adjustment/
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/About_spatial_adjustment/001t000000t5000000/

Note - In ESRI terminology, "Georeferencing" is for raster data, "Spatial Adjustment" is for vector data.

Re: Beginner Problem Projecting CAD data

KarlWilson — Tue, 05 Mar 2013 06:32:39 GMT

Just saw this too:
http://resources.arcgis.com/en/help/main/10.1/#/About_georeferencing_CAD_datasets/001000000010000000/

Re: Beginner Problem Projecting CAD data

AletheiaBouknight — Tue, 05 Mar 2013 15:41:58 GMT

Thank you very much for your response! The links have been very helpful. Unfortunately, resurveying the data is not an option, as it is an archaeology site located in the Southwest that has since be reburied. Because of the fact that it is an archaeology site, there are few/no visible geographic references either. I think I may have to continue without actually placing it in the "real world."

Re: Beginner Problem Projecting CAD data

NeilAyres — Wed, 02 Sep 2015 11:22:16 GMT

If it is actual paper you can just use a set square and the scale bar to offset 3 other cords from your 1 known point.

A similar procedure applies if the data is digital. You would have to figure out (by examining the scalebar in the drawing) if the digital units are actual real world units or some fraction of them.

Re: Beginner Problem Projecting CAD data

NeilAyres — Thu, 03 Sep 2015 12:45:43 GMT

Its just simple trig.

Make a sketch.

Offset from grid = 6.5deg (in this example, to the right of north).

If adding an offset of 100...

newX = KnownX + Sin(6.5) * 100

newY = KnownY + Cos(6.5) * 100