July 01, 2008

MSD: Leveraging CAD Standards

Which came first the Grand Canyon or the river at the bottom of it? Did the Colorado River carve it, or fall into it? By just looking at it certainly seems like the later. I got a chance not only to visit the Grand Canyon on my recent trip, but also followed the headwaters of the Colorado River down the Rockies into Utah until it headed south to the Grand Canyon while I headed west. Southern Utah seems like another even bigger Grand Canyon from the highway…just without a river.

Instead of defining a whole new path of interoperability, the Mapping Specification for DWG, MSD, falls completely within the existing DWG file data constructs and file format to provide a means to let GIS information persist between ArcGIS and AutoCAD workflows. In ArcGIS 9.3 a small change was made to the way CAD files were read to look for a simple query and entity attributes encoded on the entity’s extension dictionary in a DWG file.

I often need to share basemap parcels and attributed infrastructure data from the enterprise GIS with private developers and design contractors that use simple AutoCAD. Using ArcGIS 9.3 these contractors can use the GIS information in plain AutoCAD. Previously the best I could do was create blocks with attributes as points and simple geometry. Sharing attributed lines and polygons was always awkward in plain AutoCAD.

In AutoCAD I can add information exported from ArcGIS. The GIS feature classes when exported create MSD feature class definitions and a copy of the GIS schema in AutoCAD for me to use. I am now able to populate attributes on standard CAD entities using that schema. Inside AutoCAD I can simply add to the data on the AutoCAD layer that is used as the MSD feature class definition criteria. If ArcGIS ever opens the DWG file again it will understand the new information as belonging to that MSD CAD feature class.

Feature Class groupings in MSD are based on a simple CAD property-based filtering query. It is very similar to the concept of a definition query on a CAD feature class added to ArcMap. Instead of creating data in a specific data or custom object somewhere in CAD, I define which entities in a CAD file participate in the feature class. Entities that satisfy the filtering criteria are considered part of the feature class.

I think it is best to use the most basic criteria to define the MSD groupings such as CAD layer names, however more complex criteria can be used. Since most CAD Standards use Layer names as the primary method of organizing data now, by defining an MSD feature class based on CAD layers or combinations of CAD Layers, I can build GIS-ready data with only minor changes to my existing CAD workflows. MSD feature classes are usable in an AutoCAD drawing either by adding the MSD feature class definition within AutoCAD, by adding entities to data exported from ArcGIS, or by utilizing a seed file with the feature class definitions already defined from either or both sources.

5 Comments:

Anonymous Lynn Kim said...

I am encouraged by ESRI's support of Autodesk's XRecord format. There is a constant tension between the GIS and CAD worlds and I feel caught in the middle at times. Back in the 90's I did a stint as an ArcCAD instructor here in the Seattle area. I was saddened to see this bridging technology go away.

This added functionality will go far in bringing two seemingly competing technologies closer together. My only frustration is that I do not have an ArcINFO level license of ArcGIS 9.3 to try out this new API. I will eagerly read about other's use of this ESRI/Autodesk interop solution.

I enjoy your photography and tie ins with your personal love of family and outdoors with technology. Hopefully my next post will be under a more official banner. Lynn Kim, Principal, Northwest Geographics, Inc.

9:33 AM  
Blogger Don Kuehne said...

Lynn,

Good news on the Licesnse level front. The next service pack of ArcGIS (9.3 service pack 1)the Export to CAD tool will be availble with ArcView for this very reason! Also the next release of ArcGIS for AutoCAD that will be free for download will support MSD for the AutoCAD user. (Available... November?)

9:58 AM  
Anonymous lynn kim said...

Don,

That is great news, especially since, as a small business owner, I have to purchase all of these development tools for both ESRI and Autodesk.

It seems, from the ESRI link:

http://www.esri.com/software/arcgis/arcgis-for-autocad/index.html

that the ability to interact with an ArcServer session is limited to read-only access? Curious how the MSD API will come into play here. Will the developer be able to generate AutoCAD, data-laden entities using the ArcGIS for AutoCAD map service? I had better do some more reading/research. The answer is probably already out there.

Thank you for your prompt reply.

11:01 AM  
Blogger Don Kuehne said...

Lynn,

Right now the MSD is a form of AutoCAD file-based interoperability, and the Map Service functionality is for Services-Oriented interoperability that leverages ArcGIS Server connections. In the future MSD may play more of a role in both.

In the next release of "ArcGIS for AutoCAD" you will be able to create AutoCAD drawings that ArcGIS desktop will see as well-formatted GIS data and also use GIS data exported from ArcGIS via MSD. I look forward to blogging more about that when it is released.

11:52 AM  
Anonymous autocad drawings said...

Wow this is a really good article

8:13 AM  

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