My House Is Not a Point

By Gary Smith

Do you remember the first time you were shown GIS technology? The smile which that introduction most certainly brought to your face may have faded over time, but I hope you are continually stimulated by the thought of new ways you can use the technology. For me, the use of 3D in GIS is like my first cup of coffee in the morning. After 30 years with GIS, the smile still comes to my face, not from traditional 2D work but from things we now do in 3D. Since I suspect that most readers of this editorial have never created a 3D GIS environment, it is my belief that GIS users have simply not thought about the available opportunities using existing 3D technology. GIS users are so entrenched in their 2D world that they don’t even know how to get started in 3D. With this editorial, I hope to stimulate you to expand your horizons and look at 3D, using currently available tools and data formats. Have you ever heard of the multipatch? If you think that 3D buildings and other landscape features cannot be treated as GIS layers, please read on.

To illustrate my point, let me describe three different ways someone might create a 3D GIS environment. All three will start with a terrain model and have an orthophoto or land cover layer draped over the terrain. The next step would be to begin populating this environment with 3D landscape features (e.g. buildings, trees, signs, etc.). Using a software package like SketchUp Pro, I can construct a building that I want to add to the landscape. How I use this building model in my 3D GIS scene is critical to the scene’s effectiveness and utility. My first option is to treat the building as a graphic that I can simply add to the scene and position wherever I desire. Needless to say, this is not what I think of doing when I work in GIS. The graphic is as dumb as a bag of rocks. It has no attributes and no spatial coordinates that would allow it to work with other features or layers.

My second option is to use this building as a symbol in my 3D scene. If you are an ESRI user, this is the easily accessible option in the ArcScene and ArcGlobe environments. In these ESRI 3D viewing environments, building symbols are associated with a point layer. The last time I looked at my house, it was not a “point.” It is an object that has a footprint, with area (and volume). The building symbol does not store attributes or know its spatial location. It must rely on its associated point feature for attribute and coordinate information. Symbols may work for the 2D environment, but not in 3D.

The use of graphics or symbols is not what I want or need in my 3D GIS. I want buildings to be GIS features. They should have attributes, know their spatial location in X, Y and Z space and be able to participate in GIS analysis. Judging by the very limited acceptance of 3D GIS using symbols or graphic representations, it would seem that most GIS users share my feelings. To make the investment of time and effort, we need buildings to be smart participants in GIS activities. If you are an ESRI user, this capability has been available to you since 1998. The multipatch is a type of shapefile designed to accommodate the 3D geometry of a building or other landscape feature. Look at page 20 of this pdf document and you will find the multipatch shapefile specifications. Space does not permit a greater explanation and to be honest, none is needed. The multipatch uses triangle strips and fans and might best be thought of as the origami of the 3D GIS environment.

Now, if the building I have created in SketchUp is saved to a multipatch format it becomes a GIS feature. My multipatch building can be added to a buildings feature class, be assigned attributes and begin to participate in geoprocessing tasks. Within my understanding, the multipatch is the only format that allows 3D objects to participate as GIS features. If there are others, please share them with all of us. Using the multipatch is the third way to add buildings to the 3D landscape. Why would someone want to present a building as a graphic or a symbol in a 3D GIS? Is it any wonder why 3D has not caught on? If we are going to do 3D, let’s do it right. Just imagine for a minute that the building we created could be an individual GIS feature class and the rooms or the floors of the building could be recognized as the individual features. This would mean that I could have the ability to show the location of all commercial office space in a 3D environment. I could develop the ability to track fire fighters in a burning building. Just think about the opportunities and see if the smile mentioned earlier does not return to your face.

So why has the use of multipatch not taken off? It is a part of the ESRI shapefile specifications and allows objects like buildings to be treated as GIS features. The reason, I am going to speculate, stems from the intense loyalty of the ESRI customer base. Since there are no tools in any of the ESRI software to make multipatch buildings, users must look to a third-party for a solution. This is something ESRI users seem very reluctant to do. Proof for my hypothesis comes by asking anyone to identify a third-party-developed extension to ArcGIS that has been very successful and does not have “ESRI” on the box. In the case of the multipatch, the only affordable option to create 3D GIS features comes through the use of SketchUp Pro. Before being acquired by Google, the developers of SketchUp (@Last Software) created a free plug-in that allows users to save their work to multipatch. Has the ESRI loyalty blinded users to the opportunity to transition to 3D GIS and start using the multipatch? It would seem so. In my professional work, we have been using the SketchUp solution for several years. The creation of this free conversion capability has made 3D GIS work possible. The folks that created the original plug-in are still working on SketchUp Pro (Version 6 is coming soon) and want to see this link to ArcGIS and the multipatch continue.

Last week I had a booth at the local high school career fair. This was the fifth year in a row that I have participated in this event. This is my contribution to GIS Day. The first few years were really slow. 2D really did not go over very well. Last year, interest took a great leap forward, partially because I had built the school in 3D and I could also show the new Google Earth. This year was by far the busiest I have experienced. Students and teachers were talking about Google Earth and a number of students had found the free Google SketchUp. I had several inquiries about possible internships. On my laptop I had the local imagery used in Google Earth and I was running ESRI’s 3D Analyst to bring the conversation back to GIS and its powers of spatial analysis. These young people get it. What is it going to take for the rest of us to see what they see and have come to expect?

As a way of measuring the user knowledge of the multipatch, the staff of Directions Magazine has created a user poll that needs your input. Please make sure to offer your input. As always, your comments to this editorial are very much desired.

Published Friday, November 17th, 2006

Written by Gary Smith

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