February 14, 2007

Create Features From CAD Layers or Color...etc

I am just now getting back into the swing of things after the big super sports weekend. I lost my voice cheering for my team, and then caught a nasty cold. I am happy to say my team was victorious; Yes in all three games. Of course I am talking about high school girl’s basketball. We had three games in 18 hours. Our record is now 10-0. Our girls have a feisty full court and half court trapping press.

The head coach and I both have daughters on the team and we still sometimes struggle to figure out what ultimately motivates our girls, different from boys who seem to have a more natural fighting instinct. From time to time we inadvertently use jargon that doesn’t translate into a girl’s world. One time during a game the coach was hoping to get some more inspiring effort from the team. He looked down the bench at the girls and exclaimed, “WHO’S HUNGRY!?”, and then quickly focused his attention back to the game in progress. I was left to field the puzzled responses from the players sitting next to me. One said quietly, “ No, I’ve got my chocolate milk (holding up the container for me to see).” Another said, “no, I already ate.” And, a third asked, “What does he got?”

The term LAYER has a different meaning in the CAD and GIS worlds. I’ve written before how CAD layers are similar but very different from GIS layers, both in how they are used and how the data is stored. In CAD a layer is a graphic property, like entity COLOR, or entity line type. CAD does treat the layer property in a special way in that visibility can be controlled by the LAYER property. But, in every other way the LAYER property is like any other CAD graphic property. The choice to organize a CAD drawing by the LAYER property is arbitrary, and often CAD drawings are organized by combinations of other properties such as entity TYPE or COLOR in addition to the layer property.

In ArcGIS a GIS layer is used as a logical name for a group of features in a map or geoprocessing operation. A layer can denote a selection set of similar features; it may include joined tables, and may also include information on how the features are to be displayed. It is often convenient to talk about a GIS layer as synonymous to a GIS feature class, but generally a layer is build from a feature class.

When CAD data is organized more or less by CAD layers a sample geoprocessing script tool like SplitByColumn can make use of the CAD Layer property of a CAD file to automate the task of converting a CAD file with data on various layers to ArcGIS feature classes based on those CAD layer properties. This general use tool will take as input any feature class and split it into multiple feature classes based on unique values that appear in a given column.

Here is an updated version of the SplitByColumn tool for ArcGIS 9.2. There is a similar tool in the CAD Sample Toolbox for ArcGIS 9.1. Changes were made to the script so that it doesn’t require Python Win and a change was made in the ways string values are recognized in columns. You can download this new version of the sample tool on ArcScripts.


Anonymous Anonymous said...


I have a simple yet complex problem that I can't solve. I have Civil 3-D and have station numbers and elevations on 22 different cross sections as labels. Is there any way to extract those labels from my drawing and put them into ARCGIS 9.1 or Excel or something so that I don't have to type 1100 labels from AutoCAD????

11:18 AM  
Blogger Don Kuehne said...

I am not the Civil 3D expert, but I do know that ArcGIS reads AutoCAD text and block attributes just fine. The question is what type of entity does Civil 3D create? If its a custom object can it be exploded or exported to plain AutoCAD entities? Can the data be exported to a shapefile from which you could generate Text Labels from attributes? You might want to read my blog posts about custom objects or object data: http://giscadblog.blogspot.com/2006/12/mysteries-of-autocad-object-data-part_18.html

2:35 PM  

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