problems georeferencing a dwg file

Question

I am having trouble fitting a dwg file to the display and existing base map, georectified image and polygons within my workspace.  I have set the coordinate system to WGS_1984_UTM_Zone_56S but it seems to be way off - like of the base map.  I can get it to display in a new workspace and when adding a new base imagery it has appeared but of the world projection.

Any ideas on what I am doing wrong and how I can get it to fit my display on the zoomed in aerial imagery?

MichaelLohr · Answer

I come across this from time to time and here are some things I always start checking.

* Does the CAD file have a coordinate system internally defined? Like Chris said, many don't. If it doesn't, but the coordinates still match the data frame coordinate system, it will still display correctly, after getting the ESRI message about your "data missing a spatial reference and able to display it but not reproject it".  This is a tip off that it might not display correctly. You have to know what the coordinate system of the CAD file is intended to be, even if it is not defined in the DWG.
* Is the base imagery being used have a coord system that really matches what you have the data frame set to? Cross check with imagery from another source. If it really is Zone 56 and you say it is Zone 54, obviously that won't work. I have seen mis-displays where the CAD file was correct and the base imagery was incorrect.
* Go to your CAD staff, if you don't run CAD, and insert imagery of a known source and coord system. If it matches then you know your system.
* Go to a local surveyor who would be familiar with coordinates in the area where the CAD file depicts data. He may be able to tell you a probable coord system for the CAD file.
* I have created Projection (PRJ) files to store with the CAD file when the coord system does not match the data frame system.
* If all else fails, and you know where on your data frame imagery the CAD file should be, and there are enough photo identifiable sources you can pick out from the CAD file (like road intersections maybe), then you can georeference the CAD file. If your CAD data is good and just an issue with figuring out what the coord system is, you should not have to do this.

WesMiller · Answer

Try selecting some points lines or polygons in the CAD tables and then zoom to selected that should get where you can see it.

KarenHodge · Answer

It should be able to zoom to the layer, but sometimes CAD drawings have single entities at 0,0 that make it appear that zoom to layer isn't working correctly because of this one small feature way out in the distance.

Another useful technique is to use the georeferencing toolbar's "Fit to Display".