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Converting .dwg files   Matthew Martin Jun 02, 2006
Re: Converting .dwg files   David Lamb Jun 02, 2006
Re: Converting .dwg files   James Hemphill Jun 05, 2006
Re: Converting .dwg files   David Lamb Jun 05, 2006
Re: Converting .dwg files   Matthew Martin Jun 08, 2006
Re: Converting .dwg files   David Lamb Jun 08, 2006
Re: Converting .dwg files   Don Kuehne Jun 09, 2006
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Subject Converting .dwg files 
Author Matthew Martin 
Date Jun 02, 2006 
Message I recently received a ".dwg" file, which to the best of my knowledge is a drawing file from AutoCAD software. When I tried adding this data into ArcMap I got my favorite message, "This data is missing spatial reference. The data can be drawn in ArcMap, but it can not be projected." After I received the message I was able to view the file in ArcMap. Can this file be used just like any other shapefile or do I have to import it to a shapefile? Is there a way to convert a ".dwg" file into a shapefile? Any help with this issue would be greatly appreciated. Thanks in advance.

Matt 
   
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Subject Re: Converting .dwg files 
Author David Lamb 
Date Jun 02, 2006 
Message I'm using ArcMap 9.1, so my description is for that version. You can add the dwg file just as you would a shapefile. ArcMap will break up the drawing into the different vector formats - points, lines, polygons, etc. A drawing contains all of these features in one format, whereas shapefiles only allow you to store one type of feature. Then in arcmap, you can right click on the layer that you need, --> data, --> export data. This should let you export to a shapefile. Then you can assign a projection to the shapefile.

Another option if you have access to Autocad Map, or autocad map 3d is to open the drawing there. And use map's export function to export to a shapefile. This option gives you more control over what to export, so you don't have as much clean-up.

Hope this helps,
David 
  David Lamb 
   
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Subject Re: Converting .dwg files 
Author James Hemphill 
Date Jun 05, 2006 
Message Hi Matt,

In addition ot David's comments, before you convert the .dwg to shapefile you will have to georeference it in AutoCAD first, taking a select few points and assigning them to a British National Grid Coordinate...

You will then be able to view the .dwg in context with your other shapefiles...

James 
  James Hemphill
GIS Programmer/Analyst 
   
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Subject Re: Converting .dwg files 
Author David Lamb 
Date Jun 05, 2006 
Message I've had better luck assigning the projection to the shp file post export. I usually export to a shapefile from AutoCad Map though. Like most things there are at least 2 ways of doing something. Of course this all depends on whether or not you know the projection of your dwg. Sometimes with dwgs, there is no real world coordinate system assigned, and is just a coordinate system specific to the site, like James was saying. :)

David 
  David Lamb 
   
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Subject Re: Converting .dwg files 
Author Matthew Martin 
Date Jun 08, 2006 
Message Thank you Dave and James. The information that you have provided to me will be very beneficial. In regards to the georeferencing...I know where this .dwg file is located spatially. Couldn't I just do the georeferencing in ArcMap? Thanks again.

Matt 
   
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Subject Re: Converting .dwg files 
Author David Lamb 
Date Jun 08, 2006 
Message Yep, just define the projection in arccatalog for the shapefile that you created from your dwg.

David 
  David Lamb 
   
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Subject Re: Converting .dwg files 
Author Don Kuehne 
Date Jun 09, 2006 
Message CAD Feature classes can be used just like shapefiles for display, query and analysis, however they are read-only. If you want to create a shapefile out of a CAD feature class or an ArcGIS layer that is based on a CAD feature class (that may have a definition query to filter the data, for example) you can use any geoprocessing tool or ArcMap user interface tool that can copy data.

Geoprocessing tools like COPY FEATURES, FEATURE CLASS TO FEATURE CLASS, APPEND and MERGE are all examples of GP tools you can use to create any ArcGIS feature class from CAD features classes including shapefiles. The type of data you create from these tools is dependent on the data type you specify as the output. There aren't separate tools necessarily to create different kinds of feature classes. You can for example open and edit session in ArcMap and copy CAD data into any other ArcGIS feature class open for editing.

By the way if you don't like the message for spatial reference just create a projection file for you CAD data. It is just file, so if you have a lot of data in the same projection, you can just copy one projection file so that it has the same name as the drawing with the .prj extension.