Terrains

Terrains are 3D views of Surfaces. Surfaces are raster data sets that may be seen either in 2D or in 3D. The default view for a surface is as a 2D image. Clicking open the surface will show the surface in a 2D view like an image.

$images\img_canyon_surface.gif$

When a surface is imported, a terrain component for that surface is automatically created.

$images\sc_surface_terrain_proj.gif$

Terrains are shown under their parent surface in the project pane hierarchy. Creating another terrain for the same surface will also show it under the parent surface.

$images\sc_surface_terrain_proj_01.gif$

Create a terrain for a surface by right clicking the surface and choosing Create - Terrain.

Additional terrains may be created for a surface and each such terrain can have its own coloring and other characteristics. Creating an additional terrain for a surface does not require any more storage space since terrains are just different views into the one data set contained in the surface. An unlimited number of terrains can be created for each surface. If desired, the default terrain created for a surface may be removed so that the surface has no terrains.

Clicking open a terrain will present a 3D view of the data in the surface.

$images\sc_canyon.gif$

Once a surface is imported into Manifold, we can see it as an image by opening the surface, or we can see it in a 3D terrain window by clicking open the surface's terrain in a terrain window.

When open, the terrain window shows a view of the terrain from a particular viewpoint, as if seen from a camera at that position. The initial view is seen from a camera position at the center of the data set. What is seen in the window may be adjusted using keyboard navigation commands to alter the position of the camera, the direction it is pointed, and the field of view. In addition, we can use Linked Views to navigate to different locations in the terrain.

Controlling the Appearance of the Terrain

The contents of the terrain window are controlled by menu options that appear under the Terrain menu. These options also appear in the context menu when right clicking into a terrain window.

Open Surface	Open the parent surface for this terrain.
Surface	Specifies how the data surface that defines the terrain should be visualized. Includes options such as the texture used for the surface, the color determined by the elevation, the level of details computed, the size of the data set in view and whether the surface is shown with walls and in wireframe style or not.
Overlay	Overlay the terrain surface with images or with drawings. Specifies options to be used to display objects from drawings.
Clouds	Display synthetic "clouds" in the sky in accordance with given options.
Fog	Apply a haze effect that can appear as fog or as a subtle haze in the distance. Provides a greater sense of reality and depth.
Lighting	Choose options for creating highlights and lowlights in the surface to represent the angle of lighting.
Water	Create an opaque or semi-transparent "waterline" plane of given color. Used to simulate waterline effects.
Snap to Surface	Forces the "camera" from which the terrain window is seen to hover just above the surface by applying slight gravitation to camera movement.

Note: The Snap to Surface function assumes the camera begins above the surface so that gravity pulls it down to the surface. If the initial camera position is below the surface the camera must first be moved above the surface using a keyboard Q command.

North Arrow

In addition to the above controls, use View - North Arrow to show or hide the "compass" North arrow in the terrain window. We can also right click on the North arrow in the terrain window to hide it or to change alignment or properties.

Saving Terrain Views as Images

The Tools - Make Image command captures the current scene displayed in the terrain window as an image. This command allows us to specify the pixel dimensions, and thus the detail seen, of the image.

$images\sc_terrain_make_image_01.gif$

For example, suppose we open a terrain window like the one above. This shows a view into a terrain created from the Montara Mountain sample surface. We can use Make Image to create an image of this view, for example, if we wanted an image to use in a brochure or to include in some other document.

Suppose, however, we would like to capture this view at higher resolution that seen at screen resolution on our computer monitor. If we savethe image at screen resolution and then we print an enlarged version of the image within a document such as a poster, the image would appear overly pixilated. To see this effect, consider the region of the view marked by the red box.

$images\sc_terrain_make_image_02.gif$

When enlarged (as might occur when printing the image in a large size in a poster) we can see the detail in the terrain is limited by the screen resolution of the view. We can create the image with resolution higher than screen resolution by simply specifying a larger number of pixels to use for the image in the Make Image dialog.

$images\sc_terrain_make_image_03.gif$

For example, we might specify that the image be created in a pixel size of 2325 by 1450 pixels, about five times the resolution of the original terrain view at screen resolution.

In that case, when Manifold creates the image from the terrain view it internally will re-compute and re-render the terrain view at higher resolution so that the view will be seen in the image at the desired number of pixels horizontally and vertically. This shows the same view with greater detail.

$images\sc_terrain_make_image_04.gif$

The view above shows a small portion of the resultant image (which is too large to appear in Help), zoomed so that it shows approximately the region marked by the red box in the original terrain view. We can see that the distant mountain peaks that were rendered in an overly pixilated manner at screen resolution are now rendered in much higher detail.

Saving Terrain Views in the Views Pane

Terrain views may be saved in the Views pane to go back to the same view at a future time.

Keyboard Navigation

In addition to the keyboard arrows, Manifold uses keyboard navigation shortcuts to control the view seen in the Terrain window.

W	Move forward.
S	Move backward.
Q	Strafe Up. (Move vertically up)
E	Strafe Down. (Move vertically down)
A	Strafe Left. (Move horizontally left)
D	Strafe Right. (Move horizontally right)
SHIFT	Pressing the SHIFT key with any of the above key commands will increase the effect of that command.
Up / Down Arrow	Tilt view up / down to +60 or -60 degrees from horizontal.
Left / Right Arrow	Rotate view left / right.
+	Increase field of view (up to 130 degrees).
-	Decrease field of view (down to 30 degees).
*	Reset field of view to 90 degrees
/	Move camera position to center of terrain.

The keyboard shortcuts are designed to allow "two handed" fast keyboard navigation as favored by experts in various computer tactical games. Strafe is Quake-speak for moving sideways or up/down without rotation. A Q move is thus the same as moving straight up, as in a helicopter.

To fly upward from the terrain surface, make sure that Terrain - Snap to Surface is unchecked. Next, either use Q to fly directly upwards or use the keyboard up arrow to rotate the view upwards and then use W to move forward. The Q move lifts us up as if in an elevator or helicopter moving straight up. The up arrow followed by a W is like angling an airplane upwards and then flying forward and up the angle.

Keyboard Shortcuts for Z Scale in Terrain Windows

With the focus on the terrain window we can use the following keyboard shortcuts to modify Z scale.

Page Up	Increase Z scale by .01
SHIFT-Page Up	Increase Z scale by .10
Home	Set Z scale to 1.0
Page Down	Decrease Z scale by .01
SHIFT-Page Down	Decrease Z scale by .10

Performance Notes

Manifold's terrain view window uses the OpenGL subsystem in Windows for 3D visualization. Manifold requires a functioning OpenGL subsystem to display terrains. If there are no OpenGL capabilities in the system terrain windows will be blank when opened.

The visible performance of a terrain window is determined by two factors. The first factor is the time required for Manifold to access data and to generate parameters for rendering (heights, colors and textures). The second factor is the time required by the OpenGL system to process the generated data. Because Manifold is so fast at computing terrains, quite frequently the limiting factor in processing speed is the speed of the OpenGL system, not the time it takes Manifold to fetch data and set up the view.

It is therefore critically important that your OpenGL system is as fast as possible. The speed of the OpenGL system will depend upon the ability of the video graphics card to support OpenGL in hardware as well as upon the quality of the OpenGL drivers in use, which are normally provided by the graphics card vendor. For terrains, charts and other 3D work, get a fast graphics card with OpenGL support in hardware and lots of local graphics memory. The manifold.net team recommends cards based on NVIDIA chips. It is critically important to use good drivers. Efficient, well-written drivers are more important than raw hardware capability.

Check your graphics card vendor's web site for their latest drivers for your version of Windows. Check also the web site for the chip vendor who makes the graphics chip used by your graphics card. The chip vendor will often provide faster drivers than those available from the card vendor. Using good drivers can make the difference between smooth "fly through" motion and very slow, jerky motion in terrain views.

For example, during the development of Manifold System a number of low-cost (under $100) AGP graphics cards using NVIDIA chips were installed to test terrain window performance. When using the drivers packaged with the cards the terrain window moved painfully slowly. Several seconds were required for each slight scene change when a key was pressed to move forward, backward or to rotate left or right. After downloading and installing the latest graphics driver from the NVIDIA web site the terrain window provided smooth motion, "fly-through" quality graphics. The graphics motion seemed literally hundreds of times faster with the latest driver.

Because the quality of the graphics driver has such a great effect on the performance of the card it can be difficult to purchase a graphics card on the basis of hardware specifications only. Some of the best-known brands in graphics cards have surprisingly poor graphics drivers for OpenGL and DirectX, and some of these best known brands are also very poor at providing timely support for new versions of Windows such as Windows XP x64.

An especially frustrating situation can arise when a chip vendor sells a special version of a common graphics chip to a laptop vendor for use in a built-in graphics capability. In such cases it is frequently the case that the drivers initially shipped with the laptop are not as fast as those developed later on for the graphics chip. It is possible that users will have to wait for the chip vendor to release a special version of updated drivers to the laptop maker and then wait for the laptop maker to release the updated drivers to the user. In some cases, even famous name laptop makers have "orphaned" some products by failing to provide improved drivers for their graphics systems or even by failing to support more recent versions of Windows, such as XP.

One strategy for avoiding such problems is to buy laptops that use NVIDIA chips, because NVIDIA has in the past has taken responsibility for the good performance of its products no matter how a subsequent manufacturer has used them, and has posted updated drivers on the NVIDIA website that can be used for all of its chips, even in laptops. In particular, NVIDIA has made it very easy to get 64 bit drivers, including 64 bit drivers that work correctly with AMD dual core 64 bit processors.

If you are assembling a new system, as graphics cards have increased in speed it has become difficult to buy a new graphics card that does not display Manifold terrains with great speed. If you use a reasonably recent (no need to buy the latest, hottest version) NVIDIA based card from a vendor who advertises support for new versions of Windows and OpenGL and if you also utilize the latest NVIDIA drivers, the rendering speed of terrains will be very good.

For maximum terrain viewing performance, use SLI-capable NVIDIA PCI Express graphics cards in an SLI-capable motherboard to team up two graphics processors for rendering. Prices on graphics cards are dropping rapidly: as of this writing, installing two high-end, SLI-capable NVIDIA graphics cards with 256 MB of RAM each costs a total of $250, an amazing deal for the resultant throughput. It is often faster to use two cards via SLI than it is to spend disproportionately more money for a single card that uses the very latest, super-hot graphics chip. For example, two SLI cards using slightly downrev, but still awesome chips might be had for $150 each and the combination could end up being as fast as or faster than the latest superchip board at $750 each. Of course, if money is no object, get two of the latest boards!

A typical machine at manifold.net used to explore large terrains is an AMD Athlon 64 x2 with four gigabytes of RAM running Windows XP x64 or Windows Server 2003 x64. It will have a motherboard that can host two SLI cards with 16x PCI Express slots and run two graphics boards using whatever is a notch or two down from NVIDIA's latest chipset. Such machines can twirl full-sized terrains around effortlessly with perfectly smooth motion and no delays.

See the discussion in Performance Tips and in Using RAM and other Machine Resources for more on optimizing performance.

Tech Note

The speed with which Manifold sets up the terrain rendering job depends on the dimensions of the underlying surface, so larger surfaces will generally be slower than smaller surfaces. However, the speed penalty is semi-logarithmic: the time to generate the rendering data for a surface P that is two times as large as a surface Q is much smaller than two times the time required for surface Q. Therefore, although the speed of terrains does depend somewhat upon the size of the underlying surface the dependency is non-linear so that greatly scaling up the size of a terrain does not have that great an impact on rendering speed. The greatest impact will be the speed of the graphics system.