Overlays

Terrains may be overlaid with images, drawings, labels or even other surfaces using the Terrain - Overlay command. See the Terrain - Overlay topic for details on controls in this dialog.

To overlay a component onto a terrain:

1. Georegister any components to be used so they are in the same geographic location as the surface and terrain being used.

2. Open the terrain in a terrain window.

3. Choose Terrains - Overlay from the main menu.

4. The upper pane shows components available in the project for overlay. Check those components to be overlaid.

5. Choose display options for showing points, lines and areas.

6. Press OK.

Overlaying several components or complex components can require much computing time and will result in a long delay (potentially many minutes on a slow machine) while the overlays are rendered in the terrain window.

Example: Overlay a drawing

Using File - Import - Drawing with SDTS Files type we’ve imported the 1:24K scale SDTS DEM for the Montara Mountain, California, USGS quad. We've also imported the roads lines from the equivalent 1:24K scale SDTS DLG for this same quad. See the Combine a Surface and a Drawing in a Map example topic for details of import.

$images\sc_montara_terrain_00a.gif$

The drawing is a typical vector drawing. We've imported only the lines from the SDTS file.

$images\sc_montara_terrain_00.gif$

We can open the surface and use View - Display Options to color it with a palette. The illustration shows a view zoomed into the upper right corner of the surface onto San Andreas lake in the valley of the San Andreas Fault.

$images\sc_montara_terrain_01.gif$

We can double click open the terrain, color it using Terrain - Surface and then navigate to a position showing a view to the northwest down the axis of the San Andreas Fault.

$images\dlg_montara_terrain_overlay.gif$

To overlay the terrain with objects from the drawing we choose Terrain - Overlay . In the Overlay dialog we check the box for the roads drawing and check the Paint over terrain box as well as the Smooth line body box (for pretty, anti-aliased lines). We uncheck the Points boxes since there are no points in the drawing we will overlay. Press OK.

$images\sc_montara_terrain_02.gif$

The result shows lines from the drawing overlaid on top of the terrain. If the drawing had any points we could have checked the Paint over terrain option for points and those too would have appeared.

Example: Overlay a surface

At first glance it may seem strange to overlay a terrain with a surface. After all, aren't terrains a 3D view of a surface? It makes sense to overlay a terrain with a surface because this allows creating a terrain with one surface while coloring it with data from a different surface.

Suppose for example we have a DEM that we use to create a surface and thus a terrain that shows elevation. Suppose we also have another surface that shows abstract data, such as infrared reflectivity, temperature, samples of pollutants, or some other data that we have colored as an abstract data surface. We can open the terrain to see the 3D lay of the land and we can also color the surface by overlaying a surface onto that terrain.

$images\sc_surface_overlay_01.gif$

Using the Montara Mountain DEM again we've imported a surface and have opened the terrain in a window. The illustration above shows the terrain with no palette or texture applied in a view looking down the San Andreas Fault.

$images\sc_surface_overlay_02.gif$

Suppose we also have another surface in our project that gives temperatures as measured by airborne sensors during an overflight. We see that surface opened above colored with a palette and using shading and autocontrast to give it apparent depth, as if it showed terrain elevation.

$images\sc_surface_overlay_03.gif$

To color the terrain using the temperature scan surface, we open the Terrain - Overlays dialog and check that surface. The Areas, Lines and Points options are irrelevant when only images or surfaces are overlaid upon the terrain, so it doesn't matter what we use for them.

$images\sc_surface_overlay_04.gif$

The result is that the terrain is colored by the surface overlaid upon it. We now see not only the terrain elevations but also their temperatures.

Example: Displaying Contour Lines on a Terrain

Importing the hypsography modules from SDTS files will result in drawings showing detailed contour lines. These may be overlaid onto terrains as well.

$images\sc_contour_overlay_01.gif$

The illustration above shows a terrain with no overlays and no palette or texture. The illustration below shows the same terrain with contour lines from a 1:24K-scale SDTS DLG hypsography module. High resolution detailed drawings such as 1:24K-scale SDTS DLG hypsography files can take a long time to render. This example uses the Montara Mountain SDTS files and took 10 minutes on a 600Mhz PIII machine to overlay onto a terrain.

$images\sc_contour_overlay_02.gif$

Manifold, of course, can also produce Contour areas that can be overlaid onto terrains.

Notes

Manifold uses OpenGL to render 3D views within terrain windows. A fast graphics card with well-implemented OpenGL drivers using hardware acceleration is a must.

$images\sc_surface_overlay_05.gif$

On occasion one encounters graphics cards with bugs in their OpenGL drivers. The appearance of fine grid lines like those above when a terrain is overlaid with an image or a surface is a typical bug. The previous images were rendered on an NVIDIA card while the screenshot above was rendered using an ATI card. To remedy such problems, try downloading the latest drivers for your graphics card from either the card manufacturer or the manufacturer of the graphics chip used on the card.

If new drivers don't solve the problem consider switching to a different graphics card. The manifold.net team recommends cards with NVIDIA graphics chips since NVIDIA at the present writing has consistently turned out the best drivers for OpenGL and other graphics standards.

The "temperature scan" surface is fake data contrived for the purpose of this example. If it were real, the body of the lake would be cooler than the land.

Tech Tip

In drawings and labels, setting the foreground color to be transparent color will hide the entire object or label. Terrains respect this convention: if a drawing object or label has foreground color set to transparent color it will not appear in a terrain overlay. Likewise, if an area border foreground color is set to transparent color the area walls will also be hidden.