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Build Your Own

Apr 1, 2003 12:00 PM, by S. D. Katz

Web-Expanded

Digital Landscape Links and Photo Gallery

Sidebars
The Algorist's Dilemma
L-Systems
Smile, You're on Candid Camera

Digital Landscapes That Fool the Eye

A flooded landscape created in MojoWorld.

With mortgage rates at all time lows, maybe it's time to plow what's left of your 401k into a little real estate. Or you could load up Bryce, Vue d'Esprit, or WorldBuilder and roll your own piece of digital paradise. Since the mid-1990s, dedicated terrain creation programs have attracted a fan base of hobbyists who use the programs for digital illustration and fantasy art. Lately, improved speed and rendering quality have made them viable solutions for digital matte paintings and movie previsualization, but that's in the short term. Within the next 15 years, as processing power increases, we will see photorealistic interactive virtual worlds populated by avatars standing in for you and me. Welcome to the future of entertainment.

We see glimpses of this future in online gaming, while the underlying technology is developed in world-generation products like MojoWorld. For Millimeter readers, practical interest in this software is as a production tool; the world-building visionaries are focusing on virtual exploration. The difference has been elegantly summed up by patriarch of world-building Ken Musgrave with the phrase, “Context not content.”

A rocky MojoWorld setting.

For those of us who labor in the content-oriented camp, our standards and expectations are dictated at least in part by practical concerns and our experience with professional 3D software. To some extent, dedicated landscape generation software applications are scaled down versions of apps like Maya and 3ds Max offering an optimized tools set, lots of presets, and ease of use. Users of the heavy iron like Maya may consider prosumer applications such as Bryce and Vue d'Esprit beneath them. But these apps suggest something tantalizing: a CGI future that finally achieves the goal of the digital backlot in which locations from the Lower East Side to the Sahara Desert are downloadable databases. That reality may still be a decade or more away, but the current state of landscape generation gives a pretty good indication of how future tools will function.

While a prefab world is of interest to production designers and location finders, digital illustrators are more interested in works of the imagination. The majority of scenes made by Bryce and WorldBuilder users are fantasy or sci-fi inspired — but there are also digital artists who are interested in imagined naturalism. Not only do these landscape artists avoid actual locations, but some such as Luc Bianca, who works in France, also adhere to a sort of digital fundamentalism in which their work is generated entirely in a 3D app. They take pride in not retouching their work and phrases like “made entirely in…” often accompany landscape illustrations on digital illustration web galleries.

Xfrog's trees are "grown" using L-Systems.

This raises the issue of how landscapes are created, and philosophically what constitutes the artistic process. Historically, computer graphics have been deeply influenced by the traditional arts. Photographic texture maps, painted digital scenery, and handmade elements are an accepted part of a CG artist's arsenal of techniques. But it is also possible to synthesize surfaces, textures, and all aspects of the visual field entirely through the manipulation of code. These procedural methods are the “purest” use of computer graphics, and as computational power increases it is likely that they will begin to replace the timesaving visual shortcuts that we depend on in the visual effects industry.

Which brings us to the reality of making an acre of anyplace. Ultimately, like all CGI, the only manageable scenes are based on the classic cheats, namely texture maps rather than geometry, bump maps, billboards (plant and rock texture maps on clear polygons), cycloramas, and the rest of the digital illusionist's playbook. This is all necessary because the world is heavy, man. The scrubby weeds and ground cover in your backyard replicated in software would require trillions of polygons, far too many to be computed with today's hardware.

A selection of cacti, also created in Xfrog.

Whether you are using Bryce, Vue d'Esprit, MojoWorld, or Maya, all landscape generation uses some specific techniques. Mountains and deserts are essentially displacement maps based on grayscale images or datasets from national geological surveys (see “Smile, You're on Candid Camera” sidebar, page 58). Grasses and other simple-shaped foliage can be generated using particle systems or other efficient methods of instancing an object, while fractal and noise functions can be used to generate terrains, skies, and water turbulence. There are variations of course, but all landscape creation applications rely on some or all of these core techniques.

As the programs have evolved, many of the landscape generators have added more sophisticated rendering capabilities, including volumetric lighting, caustics for underwater scenes, and advanced cloud and atmospheric algorithms for haze and aerial perspective. At the moment, only 3D Native's World Construction Set supports High Dynamic Range Imaging maps, however, many other developers are considering this feature as well. While dynamics and simulation capabilities are available in some of the applications, realistic waves and running streams (fluid dynamics) are yet to come.

Xfrog's detailed sunflower holds up under closeup.

In this article I'll cover the most interesting and relevant landscape applications for visual effects production including the 3D apps, Bryce, Vue d'Esprit, Terragen, World Construction Set, WorldBuilder, and MojoWorld. One caveat: Products that are great for the hobbyist may not make the grade for Millimeter's audience of professional visual effects readers. The dividing line between professional and hobbyist hinges on the axis of animation vs. still imagery. Almost all the hobbyists' products evaluated can be used for 2D professional concept art and previz, but are less effective for animation.

Corel: Bryce 5

Bryce was not the first landscape creation product, but it popularized the idea of making illustrations procedurally and opened the area to hobbyists. Corel is the new developer of Bryce, and this latest version retains the MetaCreation's interface (similar to Poser's), which is a simplified, non-traditional user interface. CG artists accustomed to multiple simultaneous scene views, toolbars, and loads of moveable palettes, however, may find Bryce's dashboard deployment of tools an inefficient use of screen space.

While Bryce deserves a full review in a magazine for hobbyists, it is not really designed for the visual effects market. Bryce has reasonably good procedural terrains and very good sky and water generation, but its atmospherics are not up to the level of Vue and Terragen, and its raytracer, while improved, is slow. It recently added a network renderer, an essential for animation. The newly added Tree Lab is simply not on the same level as Xfrog, Tree Professional, or Vue. While good at far and middle distances, Bryce trees are unacceptable for motion picture visual effects. Bryce is useful as a previz tool when used in conjunction with Poser and Photoshop for 2D conceptual art. However, there are competing products that should be considered first.

E-on: Vue d'Esprit

At the moment, Vue d'Esprit and Digital Element's WorldBuilder offer the best combination of ease of use and a complete feature list of the several landscape generators that are available (World Construction Set is an interesting runner-up). That means they have realistic landscape, sky, and botanical capabilities.

Vue d'Esprit's atmospherics and raytracer.("A Day Passes" by artist Stephane Belin.)

A quick look at the images on these pages shows just how photoreal the results in Vue d'Esprit can be. Available for Windows and Mac (OS X only), Vue d'Esprit 4 is a pleasure to use. It is clearly a high-end hobbyists' tool with enough horsepower to be of use in professional production for boutiques and lone wolf CG artists.

Vue d’Esprit offers realistic landscape and botanical capabilities. (Artist: Norbert Garaj.)

Vue is essentially an advanced version of Bryce. While Bryce 5 has some nice features of its own, including a sky dome with properly positioned stars, Vue will yield more photorealistic scenes and its foliage is far superior. In Vue d'Esprit you begin the creation process by selecting an atmosphere from the preset palette, which features picons of atmospheres. You can modify these or create your own. An atmosphere defines the sun's position, the sky (including clouds and haze), and ambient light. You can change the individual parameters in the atmosphere palette and move the sun to change the time of day. Terrains, rocks, planets, and foliage are then added to the scene, and Vue smartly provides layers for these additional objects. This is essential for managing hundreds of objects.

Even after you have set up a complicated landscape, you can quickly select a new atmosphere from the presets and it replaces the existing one. This completely changes the mood of the scene. The lighting and atmospheric model in Vue are realistic over a wide range of sun positions for any atmosphere once you have made the global adjustment to the sun's brightness. (Fast results are why artists without 3D experience are attracted to landscape software.) Vue also provides a library of procedural textures including metals, rocks, liquids, clouds, animated materials, wood, landscapes, glowing, and many others. Every material can be edited and combined with other materials. Every parameter of a material can be keyframed for animation.

Vue d’Esprit provides layers for managing a number of objects.

One of the main strengths of Vue is the library of SolidGrowth foliage. Vue's trees and plants are the most sophisticated available in a general purpose landscape generator. At close range or at a distance they are extremely convincing. There is a scatter-and-deploy feature that randomly distributes plants or trees over a terrain, and because the plants are procedural, each of them is unique. The library contains about 25 plant types, and there are a few others available at the Vue d'Esprit website. However, it would be great to see even more variety.

Vue d'Esprit provides a number of primitive objects for making organic and man-made structures, or you can import models in DXF, OBJ, 3DS, LWO, COB (TrueSpace), and PZ3 (Poser4). The MOVER module (purchased separately) allows Poser animations to be imported with materials supported. The product lacks dynamics or a particle system, so falling leaves or wind effects are not possible within the program at this time.

Each Xfrog cactus is unique.

Animation has recently been added to Vue d'Esprit and like Bryce, the tools are rudimentary although the basic layout is a good start. A standard horizontal timeline with a dropdown list of objects and object properties on the left-hand side is familiar interface territory, but there are a few issues that need to be addressed. The function curves are limited, and there is only one type of keyframe. The curves are also not displayed on the timeline and can only affect the interpolation between the first and last keyframes in a sequence of keyframes.

There are a few other interface quirks, including the confusing render window — your render settings are the same as your preview settings, requiring reopening the render window to reset the output settings when you return to working on a project.

All in all, this is great software with tremendous depth in a relatively simple interface. A dose of professional input for the animation controls and the render queue would be a big step forward. If Vue was able to import and export camera data to mainstream animation software, then this hobbyists' tool would have a place in film and television production.

Greenworks: Xfrog

Xfrog by Greenworks has a well-deserved reputation for being the most sophisticated of the various organic model generators. I have created and imported several of their trees into 3ds Max, and when properly lit, they will absolutely fool the eye. Like Vue's SolidGrowth2, Xfrog “grows” organic models using what is generally known as an L-System (see “L-Systems” sidebar, page 56), which employs algorithms to imitate the natural growth process of living things. Every tree and plant generated in an L-System is unique, and the detail of finished and texture-mapped plants hold up to inspection even in closeups. Xfrog is not restricted to foliage and can also generate beautiful organic abstract models.

Which plant is real?

Xfrog is Windows-based and, along with Onyx Tree Professional, is the greenhouse of choice for visual effects companies. Greenworks offers four products based on their L-System technology: The main program, Xfrog, is a 3D organic modeler that is capable of generating trees, flowers, plants, organic-iterative architecture, and abstract structures. XfrogPlants is their library of trees available in 15 sets providing a total of 900 models developed by botanical experts. XfrogTune is a polygon-reduction product that helps reduce the data load problems that are inevitable when using realistic trees and plants in a 3D application. XfrogMLOD is a realtime solution offering multilevel-of-detail trees for gaming and interactive environments.

Xfrog supports Maya, 3ds Max, Softimage, Lightwave, Houdini, Animation Master, Cinema 4D, Poser, Vue d'Esprit, WorldBuilder, and World Construction Set; renderers include Arnold, Brazil, Pixar RenderMan, and finalRender.

A landscape created in Terragen by Luc Bianca.

Building algorithmic models in Xfrog is an additive process, and appropriately you build a plant from the ground or, at least, the component up. There are three component types: components that create objects (horn, tree, simple, and leaf); components that multiply (wreath, phiball, revo, and hydra); and components that edit (attractors and hypercubes).

You begin by selecting a component and assigning values, and link these to other components in a hierarchical structure. A component is an algorithmic instruction of objects found in nature and in that sense provides a mathematical destiny rather than a fixed description. That is why L-Systems are an ideal way to generate plants since they are actually intended to mimic cellular growth in increasingly complex arrangements. That said, making trees or fantastic organic designs is not automatic. The learning curve is several afternoons before the process begins to make sense. L-Systems produce excellent results but are by definition an experimental process: If you approach Xfrog as an illustrator or traditional model maker and expect to make a specific design of a tree, you will be frustrated. Fortunately there are pre-made models and these are available with their structure intact so you can apply component editing to an existing plant or tree. You could also buy library models and use them for your 3D scenes without ever resorting to original designs.

A scene from The Cider House Rules, finished in World Construction Set. (Eye Candy lead artist Al Magliochetti.)

But wait, we are still in the world of 3D cheats, and the surface details of Xfrog models are all texture maps. These are handled with a great deal of control, but you will be back to making bitmaps in Photoshop and putting mint leaves on your scanner. You'll be happy to know that all Xfrog models come with the appropriate texture maps.

Greenworks, located in Germany, is a very supportive company. They have a well-organized site and downloadable import plug-ins, tutorials, and notes are all clear and answered most of my questions. This is the Rolls-Royce of botanical modelers.

Onyx: Tree Professional

This stalwart botanical modeler is a close competitor to Xfrog, but takes a different approach to model making. Tree Professional comes with 260 ready-made trees that are fully editable. You can also model a tree from the ground up (there is no other way to say that). You actually begin with a random seed to start the trunk, and there are parameters such as trunk height, bottom height, crown center, bough length, length change, bough angle, bough density, bough curving, etc. Branch curving alone has half a dozen parameters. The process is straightforward and the results are highly realistic. You can even use the chain saw tool to cut branches or to slice through the trunk. Leaves are image maps on a polygon plane called a plate.

The latest version has added trunks with visible roots, bonsai curved branches, and a DFX block structure that lets the user globally apply any texture to all the leaves in a tree. Tree Pro also supplies a leaf texture CD with the software for the trees in the library. In early 2003, wind dynamics was added.

Since Tree Pro is strictly a modeling program Onyx has done a good job of supporting all the major output file types for host applications. There is also considerable control on the export parameters so you can decide the level of detail in your finished tree.

Unlike Xfrog, Tree Professional lets you determine the specific shape and limb arrangement of a tree. This is useful if you have need for a very specific “hero” tree. If you need a realistic forest, the pre-modeled trees are just fine. Tree Professional has output that is comparable to Xfrog, but it only makes trees; Xfrog has a greater variety of trees, and also generates grasses, vines, flowers, shrubs, and ferns. The advantage of Tree Professional is the ability to design specifically shaped trees using an artist-friendly interface.

Digital Element: WorldBuilder 3 Pro

The original Animatek WorldBuilder was the first really ambitious landscape generator I encountered in the mid-1990s. The animations created in WB showed fields of long grasses, dozens of trees, and flowing water. Scenes of this complexity should have brought a PC to its knees in 1996, and despite some noisy aliasing, WB was showing its ambition of creating software to build lushly foliated worlds.

From its very beginning, WorldBuilder has had a close relationship with 3ds Max and the interface remains very Max-like. They have also developed the most balanced landscape toolset including L-System trees, procedural terrain, sky, atmosphere, water, integrated dynamics for wind, and particle systems for rain and snow. At the moment, WorldBuilder and Terragen are the only products that are aimed at the individual professional animator and the desktop visual effects markets.

WorldBuilder has been developing this tool for seven years and they are being modest by calling this a 3.0 version. WB offers procedural solutions for all aspects of landscape creation as well as the widest range of 2D cheats. There are also numerous innovations beginning with skeleton lines (a method of drawing a profile for a terrain that is similar to lofting). This is a more direct modeling technique than painting a grayscale map or image-editing a DEM in Photoshop. However, skeleton lines can be combined with other methods of terrain creation as well. Splines are also used as a way to place texture maps in discrete areas of terrain. That means a small area of a mountain or cliff side can be assigned a texture, shader, or a patch of grass that is contained within the spline-defined area.

The vegetation in WorldBuilder is procedural and includes a CD library of trees, plants, and grasses and a complete L-System for creating user-designed foliage or editing library models. Like other aspects of the program, 2D solutions supplement the full 3D models, and tools for making flipboards mapped with trees are built into the workflow. Another area that offers 3D and 2D solutions is clouds. There are several options including full volumetric clouds, procedural 2D clouds, and combinations of the two on layers.

The water simulation capabilities are unique within the landscape creation arena, and WB offers dynamics that allow a leaf to float on the surface of water and float down a stream. As for matte painting, WorldBuilder's renderer has a painterly, illustrated look that is naturalistic, but not as purely photographic as Vue d'Esprit or Terragen. In fact, WB is the only landscape product listed here that does not employ a raytracer. Depending on the environment, an artist can push WorldBuilder to match seamlessly with a film backplate, however, WB's renderer tends toward a particular softness.

Planetside: Terragen

This remarkable shareware program has a loyal following of artists around the world. Currently available for Windows and OS X, the product is capable of very nearly photographic results. Developers Matt Fairclough of Digital Domain and his partners hope to release a fully productized version within two years. This is the first landscape generator written by a visual effects artist working at one of the premiere houses. Fairclough has suggested that there may be a light version for hobbyists, but it is clear that this work in progress is destined to become a serious production tool.

Currently, Terragen offers terrain, cloud, and water procedurals, with add-on scripts for animation, camera control, texture mapping tools, etc. You really have to visit the site (www.planetside.co.uk) to learn the latest news. The next major feature is support for Xfrog plants and trees. Edging out Vue d'Esprit, Terragen has the most convincing atmosphere models, as the work of Luc Bianca will attest.

The interface is remarkably simple, partly because the product has a limited feature set, but you can turn out a landscape within a few minutes of opening up the program. This was a refreshing discovery since I half expected a product designed at DD to be one step removed from command line code. That's definitely not the case, and there is a very good tutorial to get you started.

Pandromeda: MojoWorld

Let me begin with the advice that anyone interested in computer graphics technology and its application to the imagination should really get ahold of this product. MojoWorld is as much a vision, dream, and concept of the entertainment future as it is a landscape generation application. Reading the wonderfully designed manual and beginning to play with the possibilities of the software reminded me of a more naive time in computer graphics less than 10 years ago, when dreamers and visionaries could defy the marketplace and create software just to do great things. Ken Musgrave, the current dean of landscape creation and the man behind this far-reaching project, is keeping that spirit alive in MojoWorld.

Millimeter will tackle this product in-depth in a future review, but here are the basics: Musgrave is passionately interested in realtime environments and procedural landscape art rather than production tools for the motion picture industry. MojoWorld is more than just one product: MojoWorld Generator 2.0 and MojoWorld Transporter (also in a Pro version). Transporter is an exploration tool that lets you travel in universes that you download. You can render these worlds and make some global changes, but you cannot create planets or terrains. Transporter is aimed at the community of MW users so they can share their experiences.

Generator 2.0 is the beef. It's entirely procedural, so the files are absurdly small. You can fit several densely complex worlds and their moons on a floppy with room to spare. The texture generator is the most advanced I've seen, and the atmospheres are very good. The interface is non-traditional and may take some getting used to, but overall the workflow is intelligent and generally fun. And image quality is superb.

Currently in Version 2.0, the experiment is in an early stage of development — it's clear that Musgrave's vision requires 1000 times more processing power. The dream here is a deeply imagined “inhabitable” cyberspace. If that future is not quite here, at least MojoWorld gives us a great travel brochure.

3D Nature: World Construction Set 6

One of the oldest dedicated landscape generators, WCS began on the Amiga as a tool for city planners, geologists, architects, and civil engineers. WCS specializes in modeling real locations because that's what the majority of their users do. The product has added a powerful feature set over the years and clearly worked hard on their image quality, but this is not a product that had any initial interest in motion picture production. Many of the conventions and UI are going to flummox traditional 3D animators on Windows or the Mac version, but WCS makes the extra effort to learn the program worthwhile. While WCS would not be my first or even second choice for rendering realistic terrains, this software is outstanding for site planning for movies, exterior set design, and general previsualization.

Here's why: Almost every landscape creation product can import United States Geological Survey data (mainly digital elevation models — DEMS), however, there are several flavors and file formats, and WCS has a wizard to make this easy. The founder is a geologist, so tech support has expertise in the agencies, products, and providers of USGS materials. WCS goes beyond creating heightfields from DEMs for chunks of territory — the product understands that any DEM is a location on the planet and can place your landscape at the right longitude and latitude on a spherically accurate representation of the earth (whole earth data comes with the program). This makes possible one of the cooler features, which is the ability to click on any part of a terrain in a perspective view and find the distance from the camera as well as the exact longitude and latitude.

In addition to DEMs, WCS can import satellite photos and aerial photography. When coordinates are supplied with the image, it can be automatically lined up with a DEM-generated terrain.

Because ecosystems, forestry, parks, and landscape architecture are critical aspects of the kind of work the majority of WCS users do, the product is particularly good at understanding accurate representations of local flora for a given area. The community of WCS users is an excellent source of information and expertise for moviemakers who need specific data about a location and a way to experiment with sets and camera angles before visiting the site.

WCS has an up-to-date feature set including volumetric clouds, volumetric atmospheres, procedural textures and terrains, depth of field, motion blur, and a tree library (2D only) that emphasizes large data sets over photorealism. WCS flat trees are very fast to render and respond interactively to volumetrics and light.

This is the application to buy for real world location planning and site previsualization.

A New Art?

Are procedural landscapes the end of handmade art? Well, no more than photography replaced painting, which was a widespread fear in the 19th century. Still, photography has become a major tool for painters and illustrators with optical devices being used as early as the Renaissance. A tour around the Poser, Vue, and Terragen web rings is a surprising introduction to a groundswell of amateur, self-instructed digital illustrators. Just five years ago it was extremely difficult to find anything but tacky, poorly crafted illustration, and this is no longer the case. The computer has democratized art on the Internet and created an open-source community of artists who share and comment on each other's art in an encouraging and cooperative spirit.

Simultaneously, the creation of realtime worlds points to the evolution of narrative art or at least the spatial conditions under which we are encouraged to suspend belief. The technology is here for both matte paintings and online exploration. This is manifest destiny set in cyberspace without the displacement of indigenous cultures. No guilt and lots of fun.

Sidebar

THE ALGORIST'S DILEMMA

It all began in the 1970s with mathematician Benoit Mandlebrot, the father of fractals. The leap from math to terrain was made when he realized that certain mathematical functions generated lines that resembled mountain peaks. Mandelbrot became fascinated with the idea of creating worlds based on procedural methods including atmospheres, bodies of water, and planets.

In the 1980s Ken Musgrave was accepted into Mandelbrot's fold at Yale as his computer programmer. Musgrave, who started college as an art student and ended up with a doctorate in computer science, became hooked on digital landscape creation and has made it his life's work and art. Generally considered the premiere expert in the field, Musgrave was on the team that created Bryce and is now the man behind MojoWorld.

While fractals are borne of mathematics and share certain similarities to the things they are used to imitate, they are essentially a counterfeit of nature. In other words, while artists who use computer algorithms to create art (some have given to calling themselves algorists) may disparage the use of bitmapped photographic or painted textures in landscape creation, physicists are similarly unimpressed with the algorist's fractal methods. That's because the fractal generation of natural objects does not take into account physical or dynamic processes. Erosion and water turbulence in a procedural landscape are usually illusions based on noise functions, not gravity, friction, or fluid dynamics. Most of the time, fractal landscapes are more illusion than physics.

Sidebar

L-SYSTEMS

Introduced in 1968 by biologist Aristid Lindenmayer and bearing one letter of her surname, L-Systems use algorithms to formally describe the development of multicellular organisms. This mathematical imitation of plant development is ideally suited to modeling branching structures whose interconnected parts change in number dynamically — in other words, foliage. But we can go back to 1904 to find the origin of the earliest L-System, thanks to Helge von Koch, a mathematician who wrote a formula that when reiterated, could generate what is called the Koch snowflake or Koch island.

Look familiar? Like a fractal perhaps? An L-System is based on fractal math. As you know, 3D software programs have been using fractals to generate landscapes and other organic forms throughout the history of computer graphics. L-Systems are based on the concept of rewriting. Rewriting defines complex objects (like trees) by successively replacing parts of a first basic object called an axiom. Rewriting rules are called productions. The process begins when production rules are applied to the axiom — this is called a string. Subsequent strings are generated by using the initial string as the input.

One result of this process of reiteration is that the strings grow in length. More importantly, the growth and the patterns it yields continue to exhibit characteristics of the original string while yielding new patterns. These last two sentences describe the L-System and in a visual sense, the growth and development of a dandelion. This process is called morphogenesis. All of this will be on the final.

The value of an L-System is that it is a mathematical model for organic growth. This is great for CG artists because it allows a plant to be animated from seed to blossom. At the same time, by strategically introducing randomness into an L-System, plants of the same type can have subtle variations while preserving an accurate botanical description of the plant.

Interested in more of Lindenmayer's work? Read The Algorithmic Beauty of Plants by Przemyslaw Prusinkiewicz and Lindenmayer.

Sidebar

SMILE, YOU'RE ON CANDID CAMERA

Yes, we are being watched and tabulated. The surface of the earth is the subject of spy photos, weather maps, and geological surveys and is calibrated according to the 24 orbiting satellites that make GPS (global positioning system) possible.

All this watching is bad news for privacy and good news for landscape generation. The entire surface of the earth has been recorded, and it's available online and much of the data is free.

The United States Geological Survey (USGS) is the sole science agency for the Department of the Interior. Their role is largely fact-finding, and this leads to a lot of maps and mapping of the U.S., as well as other parts of world including the oceans. Much of the data is sold by business partners of the USGS.

If you need to crash an asteroid into the San Francisco Bay and want to model that area, you could buy satellite photos and topographical maps, but DEM data is what you need for digital terrain creation. A DEM is a digital elevation model and it's a representation of the topology of the earth in raster form. It's the common format used by every landscape generation software. DEM data is available on the USGS website for all of the U.S. There is also similar data for Mars (DTM) and Venus (GTDR) available from NASA's Planetary Data System (PDS). All this data can be downloaded or purchased as CD-ROMs.

The USGS has a cool site that lets you quickly select a map for any area in the United States (http://edcftp.cr.usgs.gov/glis/hyper/
guide/1_dgr_demfig/index1m.html). The maps are quite large, and the resolution varies depending on the region. Many DEMS use a 30-minute grid. In other words, the area covered is divided into 30-minute squares, with one minute at the equator equal to approximately 1.15 miles. No detail smaller than that will show up. However, there are DEMS that are as small as 7.5 minutes, or about 500 yards. Most of the landscape generators permit using fractals to displace a DEM-generated terrain to apply greater local detail.

Continue the discussion on “Crosstalk” the Millimeter Forum.
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