Terrain - Overlay

The Terrain - Overlay dialog allows us to overlay the terrain surface with images, objects from drawings, labels or other surfaces. Multiple images, drawings, labels and surfaces can be overlaid at the same time.

Images will be re-sampled and "spray painted" or "draped" onto the terrain surface. Objects from drawings will be converted into equivalent 3D objects and placed within the 3D terrain landscape. Colors used for drawing objects overlaid onto the terrain will be taken from their formatting in their home drawing.

To Overlay an image or other component onto a Terrain

1. Verify that the terrain and all components to be overlaid are correctly georegistered by viewing the terrain's surface and the components together in a map.

2. Open the terrain in a terrain window.

3. Choose Terrain - Overlay.

4. In the Components pane, check the boxes of the components to be overlaid. Use the move buttons in the dialog's toolbar to move components up and down to the order in which they are to be overlaid.

5. Choose options as desired for areas, labels, lines and points, and press OK.

The choices in the Terrain - Overlay dialog allow control over how drawing objects are represented by 3D objects in the terrain view.

$images\btn_layer_show_all.gif$	Show All - Show all available components overlaid on the terrain surface. Check all the boxes.
$images\btn_layer_hide_all.gif$	Show None - Do not overlay any components on the terrain surface. Uncheck all boxes.
$images\btn_layer_invert_all.gif$	Show Inverse - Invert checkboxes. Uncheck those previously checked, and check those that were not checked.
$images\btn_move_to_top.gif$	Move to Top - Display the highlighted component uppermost when overlaid on the terrain.
$images\btn_move_up.gif$	Move Up - Move the highlighted component up one position in the overlay stack.
$images\btn_move_down.gif$	Move Down - Move the highlighted component down one position in the overlay stack.
$images\btn_move_to_bottom.gif$	Move to Bottom - Display the highlighted component at the bottom of the overlay stack.
Areas	Display options for areas: Embed into texture - Show areas by embedding them into the textured surface of the terrain. Paint over terrain - Show areas by creating 3D area objects just above the terrain surface. Area objects will take their colors from formatting used in the drawing. Opacity - Opacity to use for areas drawn in the terrain. Enabled only when Paint over terrain option is checked. Walls - Check to display vertical "walls" which are the extruded vertical sides of areas shown in the terrain. Walls are drawn using the color specified for the area's border and using the Opacity specified for the area in this dialog. Enabled only when Paint over terrain option is checked. Vary height by column - Check to vary the altitude over the surface at which the area is drawn using the contents of a data field (column) called Height in the drawing's table. Enabled only when Paint over terrain option is checked. The height is reckoned over the highest location in the surface under the area. If the value of height is less than zero it is set to zero. The values in the Height column are assumed to use the same units as the surface.
Labels	Display options for labels: Embed into texture - Show labels by embedding them into the textured surface of the terrain. Paint over terrain - Show labels by creating 3D label objects just above the terrain surface. Label objects will take their style from the label style and colors used in the labels component. 3D labels will always face the viewer in the terrain window. To create 3D labels consisting of "text only" use a transparent background color for the labels in the labels component. Size - Relative size of labels. Height - Height in pixels above the surface to position labels Spacing - Interval in pixels between labels attached to lines. Piers - Check to display rod-like vertical supports under labels.
Lines	Display options for lines: Embed into texture - Show lines by embedding them into the textured surface of the terrain. Paint over terrain - Show lines by creating 3D line objects just above the terrain surface. Size - Relative thickness of lines. Height - Height in pixels above the surface to position lines Smooth line body - Apply antialiasing to provide a smoother appearance for lines. Piers - Check to display rod-like vertical supports under lines at each coordinate defining the line.
Points	Display options for points: Embed into texture - Show points by embedding them into the textured surface of the terrain. Paint over terrain - Show points by creating 2D or 3D point objects just above the terrain surface Size - Relative size of point symbol used to display points. Height - Height in pixels above the surface to position point symbol. Style - 2D icon or 3D shape to be used as a symbol for points. Frame 2D Symbols - Draw a wireframe rectangle about 2D point symbols using the foreground color used for points in the component.
Texture Opacity	Opacity to use for the generated texture when embedding labels, areas, lines or points into the terrain. 60% by default. The partial transparency used by the default setting makes the embedded texture seem a part of the terrain. The same opacity value will be applied to all overlaid components.
Preview	Check to see how options will appear in the terrain window as they are chosen.

Check one of the display options (Embed into texture or Paint over terrain) to show areas, labels, lines or points in the overlay. If neither Embed into texture nor Paint over terrain is checked, then objects of that type will not appear in the overlay.

Overlays can be very slow to initially compute with graphics cards that do not support textures in hardware. Even in fast cards, the initial computation of an overlay can take a few minutes. Once the terrain redisplays with the overlay, viewing will continue at the normal speed.

Example

We've created a map that has a labels layer over a surface layer created from the Montara Mountain sample surface from the Manifold CD.

$images\sc_terrain_overlay_label_01.gif$

To add labels to a terrain we begin by opening the terrain.

$images\sc_terrain_overlay_label_02.gif$

In the terrain we have navigated using keyboard navigation commands to a view over Pilarcitos Lake. The terrain has been colored using the Altitude palette. The view is toward the Southeast.

$images\sc_terrain_overlay_label_03.gif$

We open the Terrain - Overlay dialog and in the components pane we check the Labels component to be overlaid.

$images\sc_terrain_overlay_label_04.gif$

In the Labels portion of the dialog, we check the Paint over terrain box and uncheck the Embed into texture box. Press OK.

$images\sc_terrain_overlay_label_05.gif$

The result is that a label appears over Pilarcitos Lake just as it does in the map. The small vertical line under the label is the pier.

$images\sc_terrain_overlay_label_06.gif$

Note that when changes are made in the labels component those changes will be updated in the terrain window as well. For example, if we click on the labels layer in the map and change the formatting of the label so it uses blue background color and a label style that surrounds the letters in background color this change will also appear in the terrain window as well.

$images\sc_terrain_overlay_label_07.gif$

A good way to adjust the appearance of labels in a terrain window is to open the labels component in a second, small window and to make changes in label formatting in the labels window until the desired appearance is achieved in the terrain window. As the labels are changed in the labels window the terrain window will also be updated with labels in the same formatting.

$images\sc_terrain_overlay_label_08.gif$

Here is an example of labels embedded into the texture and shown with partial opacity.

Example

The choice of how lines are overlaid will greatly affect the appearance of lines from drawings that are shown in terrain windows. In this example, we have overlaid the Montara Mountain sample surface with roads taken from a 1:24K-scale USGS SDTS drawing.

$images\sc_terrain_overlay_lines_01.gif$

Using Embed into texture and unchecking Paint over terrain the line appears as part of the surface textrure of the terrain.

$images\sc_terrain_overlay_lines_02.gif$

If we also check Paint over terrain we can simultaneously paint the line floating slightly over the terrain. We have lowered the Texture opacity to 20% in order to achieve a pseudo-shadow effect for the line embedded in the surface.

Note that painting lines over the terrain will result in sharper line rendering since this method is not constrained by the resolution of the terrain texture. Rendering overlaid lines by embedding them into the surface texture will often lower the resolution of lines because the texture cannot be rendered within any greater pixel resolution than that computed for the surface seen in the 3D terrain view.

$images\sc_terrain_overlay_lines_03.gif$

Here we have unchecked the Embed into texture choice and have checked the Piers option. This option draws vertical supporting "piers" at each coordinate point that defines the line.

$images\sc_terrain_overlay_lines_04.gif$

Finally, we can uncheck the Piers option to show just the line itself floating slightly above the surface. It is usually important to paint lines with some height above the surface so that the line does not intersect any interpolated bumps in the surface that would hide the line. Therefore, the default Height parameter is set to 50%.

Pay Attention to Geographic Location

Note that if the terrain is located in a different place than the images or drawings that are overlaid upon it, there will be no visual effect seen in the terrain window. This may seem to be an obvious comment; however, it is easy to forget that some components have been georegistered and others have not yet been georegistered. Check georegistration by showing the terrain together in a map with any other components that are to be overlaid upon the terrain.

Terrains can be georegistered by georegistering their associated images. Any image that is to be overlaid onto a terrain should also be georegistered. Although drawings are frequently imported from formats that automatically result in a georegistered component within Manifold, it is possible that drawings imported from CAD formats or other non-geographic formats are not yet georegistered. These should be georegistered before being overlaid onto a terrain that has already been georegistered.

Notes on Resolution

A common task is to overlay an image onto a terrain to give the terrain a more photorealistic look. Since it is usually the case that images used to overlay a terrain are not exactly the same resolution as the surface used to create the terrain, Manifold will automatically interpolate colors from the image's pixels to compute the required color for each individual surface pixel used to create the terrain.

Therefore, the maximum display resolution for an image overlaid upon a terrain will be the resolution of the surface used to create that terrain. If the surface is 1000 pixels by 1000 pixels and it is overlaid by an image that covers the same region in 10000 pixels by 10000 pixels, then each surface pixel will be colored by an interpolation of the 100 image pixels that fall within it. The resulting terrain will not appear to be "painted" with an image as detailed as the original image used for the overlay.

To allow use of greater detail from images that are higher resolution than the surfaces in use, use the Surface - Resize command to increase the number of pixels used by the surface. Alternatively, use a higher resolution surface covering the same region.