January 22, 2007

The Universal CAD Projection File

My daughter’s basketball team that I help coach is off to a great start. In two freshman contests we are 2-0. These same players with Elise forming our Junior Varsity team, won their first game against a Varsity opponent.
With our small school team we use the same coaches, essentially the same players and the same offense and defense playbook for two teams. We position the players and their rolls on the floor using just the one set of instructions.

In ArcGIS 9.2 you can use a single ArcGIS projection file to describe the spatial reference for an entire workspace of CAD drawings. By naming an ArcGIS projection file with the name esri_cad.prj all of the CAD files in that workspace that do not have their own projection file will use that file’s instructions to identify the coordinate system of the included CAD drawings. Therefore if you have a directory full of tiled CAD drawings you need only define the coordinate system once for the whole set. Be sure however that if you move a file out of that directory that you also make a copy of the projection file specifically for that drawing.
Coming up on the basketball schedule will be a weekend with 3 games in 18 hours…, Go Lady Warriors!

From the ArcGIS 9.2 Help System:

Tip

The universal projection file is for defining a coordinate system for all CAD drawings in a workspace. esri_cad.prj will apply to all CAD drawings in that folder, which do not already have a projection file designated. If one exists for a specific file it will override the esri_cad.prj file.

7 Comments:

Blogger Glory said...

I found your blog through a google search, so I figured I'd at least ask for advice.

I have an undefined CAD feature dataset. I need to project it in NAD 83 Illinois East. Shouldn't it project on the fly if I define the data frame in ArcMap? I'm having extreme difficulty doing this as my CAD experience is pretty much nill. Any help you can offer would be great!

7:29 AM  
Blogger Don Kuehne said...

You can identify the coordinates of a CAD file by creating a .prj file. You can select a projection file using the spatial tab of a feature classes property sheet in ArcCatalog. This .prj file is then recognized by ArcGIS and would project the CAD data on-the-fly in ArcMap.

Here is another BLOG post on the subject: http://giscadblog.blogspot.com/2006/02/complete-cad-spatial-reference.html You can also view more on this and other topics by following the link on the right to this blogs master index.

3:01 PM  
Blogger snowgecko said...

The universal CAD projection file is awesome! Do you have a similarly slick trick for reprojecting CAD files?? (NAD 27 to NAD 83).

Neither Project in Arc nor a VB script I found will work on CAD datasets. Autodesk Map makes no sense to me. A batch option would be the best.

3:46 PM  
Blogger snowgecko said...

I'm thrilled with the esri_cad.prj file to define the projection of CAD files. I wonder if you know how to now reproject the CAD files? They are in NAD 27 and I need them in NAD 83. A batch option would be even better! Thanks!

5:01 PM  
Blogger Don Kuehne said...

ArcGIS does not project the CAD file itself, but can project the contents in memory while your using it in ArcGIS. To actually change the contents of the CAD file itself, you might consider a secret tool found in the no-cost extension ArcGIS CAD Client:

http://giscadblog.blogspot.com/2006/06/arcsde-cad-client-10.html

2:23 PM  
Blogger Erin said...

I've just recently changed jobs and that means that Auto Cad and GIS systems are different. With Auto Cad Map version I was able to import GIS shapes files. Now that the system is Auto Cad 2008 how do shapefiles get imported from GIS? Is it still possible to do this with the different Auto Cad version?

And, will I still be able to import updated Cad files back to GIS?

If you could help me out by answering this question or refereing me to resources you'd rock!

10:32 AM  
Blogger Don Kuehne said...

Erin,

Autodesk Map is an add-on application to AutoCAD. There is a version of Map that works on top of AutoCAD 2008 that has the same utility to work with shapefiles, as your previous version. You can also use ArcGIS to generate .dwg files or .dxf files from shapefiles or any other GIS formats if you do not have or want to get Map just to read shapefiles.

And yes, ArcGIS supports CAD files created in AutoCAD 2008 like previous versions.

3:38 PM  

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