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Is there a streamlined method to bring over CAD .dwg files that have unknown coordinate systems into ArcMap as ESRI .shp files and project the coordinate system of each new .shp accordingly? I have only been able to re-draw polygons or polylines in Auto CAD, project them there, save as .shp and then bring over that way with any luck. It just seems there would be a better method for this. There will be multiple layers and multiple .dwgs to bring over and preserve integrity of.

  • Please edit the question to clarify how you can reproject shapefiles with unknown coordinate systems. Do you really mean a "known, but undefined projection"? – Vince Sep 29 '15 at 19:22
  • I...thought I commented on this Q. Anyway, is there one unknown coordinate system or many? If there's one, do you have any information on converting its coordinates to UTM or State Plane? A grid-to-ground value or rotation/scale/translation values? CAD is often on a 'local' plane system. Sometimes it's possible to make a custom prj file for the 'unknown' definition. – mkennedy Sep 29 '15 at 20:01
  • There are many unknown coordinate systems. I am assuming its local being that its CAD.... another question is if I just assign a projection to the created .shp in ArcCatalog does that suffice? – Nathan Sep 29 '15 at 20:04
  • I'm not sure I'd consider what's in the Esri KB as streamlined, but maybe this will get you started. support.esri.com/en/knowledgebase/techarticles/detail/32939 – Kirk Kuykendall Sep 29 '15 at 20:37
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There is a great website for helping define projections. It's called proj finder (I think it used to be called "pull my proj"). Often CAD drawings are in page coordinates in which case there is nothing you can do to project the data. If the projection is in the spatial reference database then this website can help you find out which one it is. Just put the map to where you think your data is then feed it some coordinates from the data. It will then give you some options at to what is the most likely projection.

Once you know the projection you can simply generate a prj file by finding the prj file at the spatial reference website.

Once you have the prj file just rename it to the CAD data you are trying to project and add it to the directory with the CAD file. So, for the CAD file "MyCAD.dwg" rename the prj file to "MyCAD.prj". If you have a boat load of DWGs and they are in the same projection you can script the production of these using shell scripting, python, R or whatever. I am working on a similar problem now. Here is my python script for generating those prj files.

import os, shutil

prj = "Full_Path_To_Prj.prj"
dwgDir = "Directory_To_Dwgs"

for i in os.listdir(dwgDir):
    if i[-4:] == ".dwg":
        shutil.copyfile(prj, dwgDir + i[:-4] + ".prj")

This should create all the prj files for each DWG you have and store them in your DWG directory.

If you want certain features as shapefiles then you can export them from the DWG via the right-click menu in the table of contents. Make sure you are right-clicking the individual geometry types and not the group layer. Alternatively you can select certain geometries and export the selections. Once exported to shapefile you can project to whatever your project's coordinate system is.

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