DEMview Tutorial

Bryce DEM Terrains

Now that you have a gray scale terrain map, let's bring it into Bryce.

Open a new document in Bryce, and create a terrain. Open the terrain editor, and use "Merge Pict" to replace the terrain with Fall River Pass junction. Once out of the terrain editor, you should see a terrain that slopes gently down towards the right. Looks a bit flat, doesn't it? Well, let's see what setting the proper scale will do. The DEMview dialog suggests using the Unity button, but don't do that just yet.

When you create a terrain object in Bryce, the horizontal-to-vertical scale starts at 4:1. To see what I mean, click on the cube in Bryce's Create palette. When you create a geometric object in Bryce, it starts out "unit" sized. You can see in the front and side views that the cube you just made is about the same height as the terrain. In the top view, you can see that the terrain is four times as wide as the cube. The reason the cube is slightly taller than the terrain is that DEMview saved the selected part of the DEM with a gray scale that mapped the full range of altitudes in the DEM. Unless the selection contains the highest and lowest elevation in the DEM file, the gray scale image won't have all 256 gray levels.

Cubes rule!

We'll use unit cubes to make rulers to get the correct horizontal-to-vertical scale for Fall River Pass junction. But how will we get 4.6 unit cubes? It's tough to get 4.6 unit cubes, but we can get 4.5 easily. When you scale down any Bryce object, the most Bryce will let you shrink it is 1/4 its original size. Two scaled-down cubes will give us a half unit for our cube ruler. Similarly, if you need to scale up a lot, you can stretch a cube to match the default ground plane size, and you'll have a 4 unit cube.

To create a 1/4 unit cube, start with the unit cube you just created. In the top view, use the arrow keys to move the unit cube out of the way of the terrain. (Tip: If you hold down the shift key while moving the object, Bryce moves it twice as far: in 1/2 unit increments rather than 1/4 unit increments.) Duplicate the cube ('nother tip: copy & paste is the easiest way to duplicate an object in place). Check the Edit Options ("!" on the Edit palette) to make sure you have center scaling off. Click on the proportional scale tool and drag to the left until the cube stops shrinking. You now have a 1/4 unit cube.

When putting together a cube ruler, it's most convenient if the cube edges are on 1/4 unit boundaries so that you can use the arrow keys to move them without affecting their alignment. The 1/4 unit cube you just created is on a 1/8 unit boundary. Align it with the unit cube by selecting both cubes and choosing "Align X" in the alignment options tool menu. Make 3 copies of the unit cube and one copy of the 1/4 unit cube, line them up, and group them to form your ruler:

Now you can scale the terrain horizontally so that its width and depth are 4.5 times its height. Still in the top view, select the terrain, and drag the X scale tool (the one with the arrows on the front of the cube) until the terrain width matches the ruler width. Rotate the ruler 90 degrees with the Y rotation tool (the edit cube that's wearing a hula hoop), and move it so that it's centered on the ground plane. Scale the terrain with the Y scale tool (edit cube with arrows on top) until its size matches the ruler. When you're done, you should have something that looks like this:

We're done with the ruler now; you can delete it. (Tip: if you do a lot of terrain rendering, it's handy to keep a Bryce scene with cubes scaled to various sizes. You can merge this scene with your DEM terrain scene for quick cube ruler assembly.) Switch back to the default view. Still looks a bit flat, doesn't it?

As mentioned in the DEMview Guide, DEM terrains look different than those Bryce creates because of the relative scale of DEM terrain data. The range of elevations in the Fall River Pass DEM is 1146 meters, and at 30 meters per pixel, a 128x128 selection is nearly 4km across. Bryce terrains operate on a smaller scale, with higher resolution. To get dramatic terrains with DEM images, you need to keep the camera close to the ground and position the camera close to terrain features of interest. Alternatively, you can make the terrain larger. Now that the Fall River Pass terrain has the correct horizontal-to-vertical scale, you can use proportional scaling to pump up the size for easier camera manipulation.

Finding the sweet spots using the ubiquitous Pyrapod

One way to pick interesting camera positions is to start with the terrain image and look for interesting features like canyons and cliffs. In Bryce, you can create marker objects and position them in the terrain using the top, side and front views. I like to use pyramids, because as you bury them in the terrain, it's easy to zero in on the precise camera location you want: X marks the spot, in the top view. Let's try this with Fall River Pass Junction.

One obvious interesting spot in this terrain is the east canyon; we can look up the canyon from the river valley. Start by switching to the top view, then use the proportional scale tool to enlarge the terrain to about the size of the Bryce window. Create a pyramid, and move it to the lower left hand corner of the image. Go into the materials editor, and give it an obnoxious diffuse color that will be easy to see in any terrain texture you might use. I usually use a bright purple color. It's also useful to give the terrain a flat-shaded neutral brown color during test renders instead of Bryce's default slightly-shiny gray. I find it easier to spot terrain features with this material:

After setting up the surfaces, set up the test render. Still in the top view, drag the blue camera box to the lower left edge of the terrain, and drag the blue camera line so that it's pointing at the center of the pyramid:

Now go to the main view, and select "Ground Camera" from the view menu. Move the pyramid using the arrow keys so that it looks like it's positioned inside the river valley, and hit page-down a couple of times so that just the tip of the pyramid will be visible above the terrain. Next, do a quick test-render to see if the pyramid is where you want it. If it isn't visible on the first pass, hit page-up to poke its apex through the terrain. After a couple of passes, your image should look something like this:

This pyramid will be your camera's tripod (a Pyrapod!). Right now, that tripod looks several hundred meters tall. Since you want the camera as close to the terrain as possible, use option-page-down to adjust the pyramid's vertical position so that it's barely visible above the terrain:

Using the top, side and front views, move the camera to the tip of the pyramid, and drag the blue camera line so that the line of sight is aimed toward the northeast. Go back to the main view, and test render to get your bearings. Then tweak the camera position as needed, pick a nice texture for the terrain, and season to taste with clouds, fog and haze. Note that to get effective haze with DEM terrains, you need to scale the terrain up very large to distant features a nice hazy blur. Here's the image I ended up with for Fall River Pass Junction:


This section of the tutorial covered a lot of ground (ahem). We brought a gray scale DEM image into Bryce, and fixed its horizontal-to-vertical scale using rulers composed of Bryce cube primitives. I described why DEM terrains look relatively flat compared to the kind of terrains Bryce creates. We set materials for test renders and used The Amazing Pyrapod to locate an interesting camera position. Bryce primitives can also be used to mark view points in the terrain: plop one down in the terrain and aim the camera at it using Bryce's top, side and front views. With a few test renders, it's easy to find just the view you're looking for.

That pretty much covers the basics of rendering DEM data in Bryce. In the next section, I'll describe how to deal with terrain features that cross DEM boundaries.