October 13, 2009

Creating Multiple CAD files from ArcGIS

When coaching sports, executing a play can be rather complex with interrelated situational options involving both rules-based and opportunistic options that are very dynamic. Once you have diagramed the play and the team has really learned it, the result is all the players doing the right thing when the coach gives a single command. When the team doesn’t learn the play in a game there is no time to explain how each player needs to respond specifically to a given situation. Which results in the meaningless rants of coaches: “Move your feet!”, “Reverse it!”, “See the floor!”, “GO!” which taken at face value are not very instructional… but they make coaches sound wise, or at the very least make the coaches feel like they are contributing.

GIS data sets can be huge, CAD files can be big. Sometimes big gets to be too big. ArcGIS is designed to accommodate large datasets by managing data from the source in ways that it doesn’t have to load all the data into memory while also employing database science to manage large queries and analysis. The drafting environments of AutoCAD and Microstation employ high-end graphics technology that promotes fast drawing of large datasets, but was never designed for large scale data management. Traditionally the CAD solution is to break up files into vertical or horizontal tiles that can be combined together by reference or to be viewed individually. Within the context of mapping these might be vertical tiles where different drawings are stacked on top of one another based on their content discipline. For example a layer of electrical distribution data, another drawing which contains the parcel and street data, another for water, sewer etc…

Another method of tiling is by geographic zone. Horizontal tiles include all of the data in each tile, but multiple tiles are used to cover a geographic area. This form of tiling also supports the idea of pages in a map book, or districts, zones or other arbitrary or gridded system of breaking up the map. These grids may be to distribute responsibility, or they may be based on, ownership or other geographic boundaries. When moving CAD data from a gridded tiling system into ArcGIS tools like APPEND and MERGE are common tools to create a seamless map.

To recreate the tiling systems of CAD, the EXPORT TO CAD tool can be used to generate multiple files from a single GIS data set. The key is to include a field in the data sets feature attribute table called DocPath. Within this field you can populate each feature’s DocPath value to control which Microstation or AutoCAD file the data should be exported to.

First you will create a polygon grid that represents the geographic boundaries of what would be each CAD file. Then populate each polygon with a value in a field called DocPath that represents each CAD file name. Then I use that grid to perform a spatial join or an overlay function and maybe the CALCULATE tool to include the CAD DocPath on each feature I intend to export. I then invoke the EXPORT TO CAD tool. Be sure to leave the Ignore Paths In Tables option of the EXPORT TO CAD tool unchecked because this is what this option is for.



Anonymous Vectorone said...

So - is the assignment of grids geographically a manual process or is that something that is automated?

Not every grid will have the same amount and types of data, so do they get balanced in an automated way when dividing them?

3:34 PM  
Blogger Don Kuehne said...

I was assuming that the polygons to distinguish your different drawings would be up to you the user.

As you have pointed out a rectangular grid might work in certain situations but in others the geography such as in coastal regions might produce empty drawings and data density might also influence how to divide the data.

I would suggest using tools in ArcGIS to count features and ballance the areas in a manual or more sophisticated automated fashion using GIS techniques beyond my expertise, GIS techniques you might employ to ballance service zones or sales territories, etc.

2:04 PM  
Anonymous Anonymous said...

Can you use ExportCad to convert ESRI schematic diagrams to DWG files ?

4:10 PM  
Blogger Don Kuehne said...

No not directly. To get your schematics in CAD you'll need to use a GP tool to convert the diagram to features. Then export the features. You may also want to label those features and convert the labels to annoation if you want the anno to get converted. Once you have feature and annotation you can export the result to CAD. If you export the data to AutoCAD you'll get the original attibute too with feature classes.

4:44 PM  

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