August 18, 2008


The Balloon Whisperer
I decided to have a traditional picnic in the park last week. We packed a basket, blanket, sandwiches, salad, and a fresh pie we had made the evening before. We found a nice little park in the canyon and enjoyed a family time on the grass under some shade trees in perfect weather. My youngest daughter Evie was enjoying the freedom of running carefree in the open field when I spotted off in the distance a bunch of pink balloons that had evidently escaped from some celebration miles away. One tradition I have with my daughter is to pick her up into the air to see if she can reach the moon. I hold her up and she reaches as high as she can. Each time we expect that maybe we might actually reach it, but when I ask her if she can, she says, …no, its too high.

Busy running to and fro in the open field I attempted to focus Evie’s attention on the significant collection of balloons floating in the distance. My daughter Evie loves balloons. After pointing out the balloons my wife and I noticed the balloons had taken a definite path toward us. They were still very high, but heading in our direction. When the large bunch of balloons neared the edge of the field I thought that it might make the reaching game a little more fun since they were coming toward us. So, I gathered here up. She reached with outstretched arms and fingers while I lifted up on my tippy toes… Then a surreal alignment of child expectations, a bunch of pink balloons, and wind currents sent the fully inflated helium decorations purposefully plummeting to earth from out of the sky directly at us! In the moment of truth a gust of wind sent the balloons racing over our outstretched hands, but as I turned round 10 feet behind me they were collected on the face of the baseball field’s backstop . I walked up to the backstop and pulled the pink bunch of balloons from the chain link and handed them to my delighted four year old. I then turned to my wife and older daughter, and together we marveled at what had just occurred. Amazing.

The default functionality of the ArcGIS Export to CAD tool creates AutoCAD files with MSD encoded data. The GIS feature layer name is used as the AutoCAD layer name and the MSD feature class criteria to define the entities belonging to that feature class in AutoCAD is that same < name =" Feature">. All the attributes included on the exported GIS layer are automatically included as attributes on the entities. Likewise any fields from joined tables would also be included, because they are included in the feature layer.

Using the default functionality of the ArcGIS 9.3 EXPORT TO CAD tool creates attributed AutoCAD files with GIS encoded data. To the AutoCAD user the data is still standard AutoCAD entities with standard CAD entity properties, it just has a little bit extra to make it more useful for those who know where to look for it. These attributed AutoCAD files are created without effort, but are created with the potential to be very effective in sharing GIS content. All you have to do is reach out and grab it.

ArcGIS desktop and server applications read MSD encoded AutoCAD files. The next version of ArcGIS for AutoCAD will also include free tools to read and write this information. Published in the ArcGIS 9.3 online help are sample scripting tools to allow AutoCAD users to work with this information from within AutoCAD. API Samples are available in AutoLISP, the programming language syntax of C# - .NET, and DWGDirect code (The DWG Software libraries published the Open Design Consortium).

August 11, 2008


Into the Wilderness

I am planning a camping trip with my daughter. I grew up understanding that the term camping was a word reserved for the act of wilderness hiking. Our family made a distinction between hiking and lesser forms of camping like car-camping, which is prone to result in too much stuff and too little place to pack it. I later learned that camping might also apply to vacationing in a cabin in the Northeast. In my youth I would often hike a week at a time in the national parks of Washington State and never see another person; deer, bears, mountain sheep, chipmunks and mosquitoes, yes, but no other people.

In planning this short overnight hike with my daughter I am contemplating the minimum amount of gear I will need to enjoy the trip. I am a firm believer that the key to camping is comfort! It is a family creed.

As with many things in life, the idea of carrying everything you need to be comfortable up a steep mountain can create opposing requirements. If you pack too much gear you won’t be comfortable carrying it. If you don’t carry enough gear you might be miserable without it.

Packing GIS data for the CAD wilderness is what MSD is all about. There are many different ways to organize data in an AutoCAD file. There are also various strategies to associate attributes with entities. These include attaching external databases, linking entities together and leverage block attributes for polygons and lines as well as point feature, adding simple text. Extended Entity data is another way to add additional information in the dwg file, most of these lack a user interface all have significant limitations. Xrecords, their container objects, the Extension Dictionary and the Named Object Dictionary, are the modern mechanism for storing non-graphical data and attaching them to entities in AutoCAD.

The Mapping Specification for DWG (MSD) is ESRI’s response to evolving technology. Leveraging these methods of storing information in a well defined and consistent way allows GIS information to be encoded directly in the drawing without resorting to the pitfalls of implementing and supporting AutoCAD custom objects that are powerful yet ambiguous additions to the DWG/DXF file and are impossible to use without the application that created them.

MSD allows ArcGIS users to share feature class data, feature class organization, and attribution with plain AutoCAD users. Likewise standard AutoCAD users can create rich GIS content with attributes for future use in ArcGIS and their own AutoCAD application needs, knowing the resulting data created in AutoCAD will be directly usable in AutoCAD and ArcGIS. Most importantly MSD allows CAD draftsman to create standard AutoCAD entities using their existing CAD standards to create this data. MSD uses standard CAD entity properties to define the criteria for inclusion in a GIS feature class and therefore uses rather than replaces existing workflows.

The MSD specification is published here in the CAD Section of theArcGIS 9.3 online help.
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