ArcSDE CAD Client #4

Storing GIS Features from CAD Entities

I was talking to my carpool partner yesterday about vacations and planning and the alike. One thing I like to do with my family vacations is to have a theme for the vacation. Past themes have included very simple things like... everything you drink on the vacation has to have an umbrella in it. We bought our own drink umbrellas and stuck them in sodas, water bottles, and the fruit smoothies we made with our daughter in the hotel room. We kept well hydrated and enjoyed very much just relaxing anywhere we were while sipping around the umbrella stick. Themes help set expectations for the trip and make it more memorable. Themes also help focus choices. If the theme is PIRATES then the choice between spaghetti and roast chicken eaten with your hands; is easy. Do we go to the maritime museum or the arcade? The choices tend to make themselves, and there is generally no dissension in the group if everyone is on board with the theme.

CAD Client will allow you to specify a gripped/fenced selection set of feature or the contents of the current drawing to be stored into an ArcSDE simple feature layer. CAD Client relies on the configuration of what is called a “Store Template” to define various options of CAD data storage in ArcSDE layer… things like do you want to store CAD graphic properties in the attribute table, if so which ones…in what existing columns? … For example storing the CAD drawing name in an ArcSDE feature attribute column would allow you to select the resulting ArcSDE features based on their source CAD drawing name. Also included in the STORE template is the option of whether I want to store the CAD BLOB in ArcSDE?

The CAD Client is an organizing definition that identifies how CAD data is going to be stored in an ArcSDE layer. Like a vacation theme it defines what gets packed into the car, where the flashlight is going to be stored, and the parameters for future decisions.

Using CAD Client to populate existing ArcSDE simple feature layers pre-supposes you have an ArcSDE simple feature layer created and accessible. Some consideration when defining your ArcSDE layers that will be populated using ArcSDE CAD Client would include: will you include columns to store CAD graphic properties; will you enable your ArcSDE layer to accept CAD blob data storage?

These are some concerns or limitations about its data storage you need to come to grips with before using CAD Client:

• CAD Client retains the full CAD definition of curves and complex objects in the CAD Blob, but the ArcSDE simple feature will be simplified with tessellated straight line segments.
  
• CAD Client allows you to store a copy of a complex object with tags or block attributes, but unlike the ArcGIS CAD Feature Class does not allow you to populate the ArcSDE feature layer attributes with these values. You will be able to store and retrieve CAD BLOBS with tags and block attributes, but that information is not accessible to other GIS applications, since the values are locked in the CAD BLOB and not extracted or included in the feature attribute table.
  
• ArcSDE CAD Client can store features of different geometric types in the same feature layer. ArcGIS only allows you to store one type of geometry in a feature layer (POINT, POLYLINE, POLYGON, and ANNOTATION). CAD Client does not store or retrieve MULTIPATCH features.
  
• You have the flexibility to store different types of geometry in the same ArcSDE simple feature layer for easy storage and retrieval (a little known fact of ArcSDE), but be aware that in doing so only the highest level geometric type would be accessible by ArcGIS. If I am not using ArcGIS to access my CAD data (stored using ArcSDE CAD Client) then I like to mix feature classes and put all the data in one big CAD BLOB repository, which makes one big pool of all my CAD content. In that way I can use a single query to access any of the data I’ve stored.
  
• The ArcSDE CAD Client software was developed before geodatabase style annotation was envisioned and only stores and retrieves CAD TEXT as ArcSDE simple feature annotation. CAD Text stored as ArcSDE simple feature annotation must be converted to geodatabase style annotation before it can be used in ArcGIS.

Continue to Part #5