February 26, 2008

Import From CAD and Chainsaws

When someone is talking on their cell phone in the car and you’re riding along, you really can’t help but eavesdrop on the conversation, albeit one-sided. I recently heard this from a friend of mine while talking with his 8yr old son on the phone:

…Did you get all the leaves picked up? ...How about sweeping the back porch? ...and the grass?.... the what?, …why? ... No buddy, you don’t need a chainsaw for that!
The girls in the back seat immediately tuned in at that last exchange. His sister quickly asked, “Chainsaw?! What is Riley doing with a CHAINSAW?!”

The right tool for the job may be less powerful and simpler than the one I might first think. There is a geoprocessing tool in ArcGIS called Import from CAD. Judging by its name, many people gravitate to the tool to make use of CAD files in ArcGIS. Its original design was to generate a normalized view of a CAD file for dissecting and reassembling into all manner of difficult and sophisticated workflows. However for most purposes it is more than overkill, it is much more work than simply opening and using a CAD file directly.

ArcGIS reads CAD files as GIS content and the process of Importing is not necessary. I can create GIS data sets like Shapefiles, or Geodatabases simply by opening a CAD file and copy-and-pasting or, using any number of tools that copy data such as Copy Features, Merge, Append, Feature Class to Feature Class, etc…

The Import From CAD tool creates a Staging Geodatabase that is a highly normalized set of tables that mimics the actual internal organization of a CAD file. The imeadiate result is less directly usable than the default CAD feature classes created by ArcGIS when it opens a CAD file. In fact when I do use the Import From CAD tool the first thing I usually look to do is link the tables together in a useful way, then create a subset of the data, and copy that data to a Geodatabase. Opening up a CAD file and using the Feature Class to Feature Class tool does that for me in a single step.

Import from CAD is a tool that does handles SPLINE geometry better than the default CAD file direct read, and can access AutoCAD Extended Entity Data. However, if I am not working with this type of data there is little reason for me to bother with the tool.

In like manner, just because a chainsaw can make short work of a rose bush, it may be just a little overkill, resulting in even more pieces for me to pick up after I’m done.

February 15, 2008

GIS and CAD Windfall

The fortune cookie after my dinner the other night claimed that I would enjoy a windfall. There was some discussion around the table as to what the definition of a windfall was, and the origins of the term.

Webster’s defines it thus:
1 : something (as a tree or fruit) blown
down by the wind

2 : an unexpected, unearned, or sudden
gain or advantage.

I didn’t think much of it at the time, but when I was taking the trash cans out to the curb that windy night and a lotto ticket came cart-wheeling along the ground to my feet,... I was intrigued. It was trash night so scraps of paper blowing around wouldn’t necessarily be uncommon, but a lotto ticket!? Surely the stars were aligning and good things were happening!

I wasn’t sure if the lotto drawing had already taken place or if the ticket was still alive. The data on the ticket in itself was not enough to tell me much of anything. However a quick check on the internet to the lotto website winining-number-server gave me my answer.

Two independent pieces of data that just happen to show up in the same place, although intriguing don’t necessarily mean anything at all. GIS and CAD interoperability is more easily trusted when I get my information right from the source, whether that source is GIS or CAD. When in ArcGIS I can use the contents of a CAD file without creating a copy of it. I certainly can make a copy of it in a GIS format if needed, but sometimes CAD file is the proper source and should be included in a map as such. The same can be true when working in CAD, getting a copy of data from the GIS basemap in a CAD format although useful can be prone to getting out of date or losing the context of how it is used in a map. How GIS data is symbolized is a large component of the value of GIS-generated maps. Directly accessing the GIS basemap from ArcGIS Server using ArcGIS for AutoCAD is one way to ensure I've got the most up to date and relevant information in its proper display format inside AutoCAD.

There is a movie of ArcGIS for AutoCAD on the same page where I can download the application for free. For more information on working with CAD files inside ArcGIS you might consider some of my past articles on the subject.

Alas the lotto ticket was no winner… perhaps I should have played
the numbers printed on the back of the fortune cookie fortune instead… hmmm... I’ll let you know!
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