三维建模之3The 3D Migration Continues

The 3D Migration Continues

Summer is over and daylight savings time is coming to an end. It was still warm and sunny in late July when we published our last 3D GIS newsletter. Between vacations and other work, the time to write our next newsletter seemed to slip away faster then the hours of sunlight in the day. This is not to say that we haven’t been out promoting the use of 3D in GIS. Quite the opposite is true. Most notable is an article that will appear in the November issue of Earth Observation Magazine titled, “3D GIS, A Technology Whose Time has Come.” If you don’t currently receive this publication, go to www.eomonline.com and consider subscribing. You will also be able to read the article there once the November issue is released.

Should I use a 3D Symbol or a Multipatch?

In previous issues of our newsletter we have tried to promote the use of the multipatch. If you want to review older newsletters go to our web site (www.gis-help.com) and click on the Newsletters link. As important as we believe the multipatch to be, we must always keep scene efficiency in mind. Using a single building as either a multipatch or as a 3D symbol will not cause any difference in the graphic display performance of your scene. What affects performance is the number of objects that must be stored in memory and rendered on the screen. In general you will have two different classes of buildings in your 3D scene. These two classes might be referenced as buildings that currently exist (geo-specific) and buildings that might be built (geo-typical). One technique used in 3D simulation to reduce memory consumption is called “instancing.” Objects that are used over and over again can be read into memory once and then instanced in the scene many times. This is the way most trees are presented in a 3D landscape. At the moment, multipatch features are not instanced. As such, having a large number of complex multipatch features in a scene can result in decreased performance. Proposed buildings might also be shown as symbols, particularly if they are repeated, as might be done to visualize the potential build-out of a parcel or larger area. As a general (certainly not hard and fast) rule, if the building is geo-typical and repeated, display it as a symbol. If it is geo-specific use the multipatch.

Creating Multipatch and 3D Symbols

If you will recall from our previous newsletters, ESRI does not provide any capability to make your own 3D Symbols or multipatch features. To make your community, you will be required to add new software to your GIS arsenal. Fortunately, this is not a very expensive proposition and we have found the exposure to these 3rd-party software packages very stimulating. The ease of use of many of these packages makes getting started a snap. One of the questions we received after the article “Essex, Vermont, Discovers the Power of 3D Analysis” appeared in the Summer 2004 issue of ArcNews related to our choice of 3rd-party solutions. Why did we pick the ones we used? The answer is fairly simple. First of all, their cost was not too great. Second, they were easy to use! Finally, they produced output that was easily read by ArcGIS and 3D Analyst.

ArcGIS/3D Analyst™ can see and use output in 3D Studio (3DS), Virtual Reality Modeling Language (VRML) and OpenFlight (FLT) formats. With a free add-on from ESRI you can also read SketchUp™ (SKP) formatted models for use in ArcScene™ and ArcGlobe™. Arranged by list price, here are the products we use:

1. SketchUp™ - $495 (This is the only product that reads and writes multipatch)
2. ModelBuilder 3D™ - $899 (Uses Wizards to help new users create models)
3. REALnat™ - $1,750 (Creates species specific tree models in minutes without the need for digital photos)

We use and sell all three of these products. To ask for a price quote or how to evaluate these products for free, send us a note at info@gis-help.com.

Expanding Your Use of 3D GIS

A school as viewed from the interior of a house located on an adjacent parcel.

At times like this, when heightened security is the norm, it is exciting to think that we can use our existing GIS database to analyze the view from within existing buildings without ever entering the structure. Consider the view of the school building from the window of an adjacent building. The view simulates very accurately what could be seen from a window, looking at an important structure, without ever going inside the private building.

Not every situation need be security-related. Imagine the commercial realtor having the ability to show a potential tenant what the view from their new office might be like, even before the building is constructed. We in the GIS community with our GIS databases are in a prime position to foster this type of use. Not only is the developer happy, but we win as well because the development community provides the new structures to keep the 3D GIS database current.

Many GIS managers are concerned with the maintenance and upkeep of their GIS databases. Just imagine for a minute that if every architect or developer were using a product like SketchUp™, all new buildings could be created and added to the GIS database without any staff resources being expended. Perhaps it is time to take a few minutes and canvas the architects in your area to see what software they use to model their new or renovated buildings. If it is something that will output to one of the 4 supported formats, you may be ready to join the 3D GIS revolution the easy way.

Have You Created a 3D GIS Scene using ArcScene or ArcGlobe?

If you would like to share some work you have done in 3D, consider writing a story for ArcNews. The guidelines for submission can be found at www.esri.com/news/arcnews/submission.html.
This is one of the best ways to share your efforts with others and expand the use of 3D GIS.

If you are uncomfortable starting a new 3D scene on your own, let us help you. Our consulting rates are very reasonable and with our years of experience in 3D development, we are productive from the very start.