August 11, 2010

Hidden CAD Properties In ArcMap

Someone dropped their cell phone into a standing body of water… again. She claims it was on the blink anyway… off to the cell phone store for the “free” phone upgrade with 2 year contract etc… but turns out the week before I was browsing on the cell provider's web site and found a clever new way to save money with an upgrade of the family’s existing phone plan to the “plus plan” that has the *same service and that is cheaper (bad sign). Apparently one of the plus’s I get with the new plan is that I don’t get any more phone “upgrades”.

ArcGIS reads the graphic properties of CAD entities (color, layer, line style etc…) as feature attributes. In recent versions of ArcMap the more esoteric CAD graphic properties are hidden from view. The reason is that many of those graphic properties such as the extrusion vector have limited application in GIS and people were doing more work to hide them. In the same spirit of simplicity feature classes defined in ArcGIS for AutoCAD don’t include these hidden lesser-used graphic properties (I can’t unhide them because they are not there), the thought being with this type of CAD feature class I intend to work with my attributes exclusively as GIS content. One exception to this I can think of is working with text or block attributes as a feature class of say MANHOLES or VALVES and I am interested in the rotation angle of the features.

That rotation angle information is accessible to me in the CAD file, but not on the named feature class MANHOLES I have set up in ArcGIS for AutoCAD. Because feature class definitions in ArcGIS for AutoCAD files are really filtered queries or “database views” of the CAD file, all of the graphic property information is included on the default unfiltered feature class views of ANNOTATION, POINT, POLYGON, POLYLINE and MULTIPATCH. I can join the two together to get all the attributes I need.

If I turn on the visibility of the HANDLE property of my MANHOLE feature class and the HANDLE field of the POINT feature class I can use ArcMap to JOIN the two layers together. I join the two layers based on the entity HANDLE field. I change the field visibility in ArcMap by using the FIELD tab of the properties panel that I invoke from right-clicking the layer in the table of contents. In this way my MANHOLE feature classes from ArcGIS for AutoCAD can display any of the CAD graphic properties supported by ArcMap including my rotation angle value.

Sometimes less is more and only because I don’t want too much. Sometimes (like when I need what is missing) less is just less. Simple = good; complex = bad is generally a good adage. Unless the aim is to confuse, like cell phone billing and credit card promotions, but I think that is a different issue all together. Good for them bad for me!

FREE hit counter and Internet traffic statistics from