Examine A Preview Mesh

Slide 1

This exercise is designed to teach you about preview meshes. Previous experience with node-based modeling architectures such as Maya® is helpful.

Open The File

Open the database and examine its contents.

  1. Start the software.
  2. Open \EXERCISES\EXAMINE_TERRAIN\EXAMINE_TERRAIN.BOX.
  3. Examine the hierarchy. This is a picture of the hierarchy.
    This is the preview mesh in the scene graph. This mesh is not the "terrain"; it is a simple visual representation of the terrain. Scenome is node-based and uses a node-based presentation of the terrain preview mesh from which the output terrain is derived.
  4. Examine the worksheet: This is a picture of the worksheet.
    This is the preview mesh geometry. This is a full-geocell preview mesh created from a DEM. This is not the final terrain; final terrain is built from this preview mesh and uses the settings in the preview mesh construction history to generate the output terrain. Instead of being dialog-based or wizard-based, Scenome is node-based. Scenome does support the concept of a wizard but that too is node-based.

Examine The Hierarchy

This instruction set contains detailed explanations of the preview mesh node-set.

  • ImportResults
    • Palette
      • Lat: [46.00 to 47.00] Long: [-122.00 to -121.00]
      • Lat: [46.00 to 47.00] Long: [-122.00 to -121.00]
    • Lat: [46.00 to 47.00] Long: [-122.00 to -121.00]
      • ExportOptionsLayer
      • OrthoImageryOptionsLayer
      • GeometryLayer: 8×8
      • ElevationLayer
      • GeographicProjectionLayer
      • DynamicTextureLayer
      • CalculateLightingLayer

In Depth

Double click each node and examine its parameters before you read about each node.

Name  
  • ImportResults
  • node is: group node
  • This group stores the preview mesh nodes and is not required but helps keep the preview mesh node-set nicely organized.
  • Palette
  • node is: group node
  • This group stores the material and texture for the preview mesh. The preview mesh is linked to this group via its Palette parameter. You can name this group whatever you like but the name Palette is used to provide a key to the purpose of the group. This group is required.
  • Lat: [46.00 to 47.00] Long: [-122.00 to -121.00]
  • node is: material node
  • This material node is applied to the preview mesh modifier GeometryLayer: 8x8 and linked to the texture node immediately following it in the scene graph. This material is required.
  • Name Derived: From the latitude/longitude boundary of the DEM. Rename if you like.
  • Lat: [46.00 to 47.00] Long: [-122.00 to -121.00]
  • node is: texture node
  • This texture node points to a file on the hard disk and is referenced by the the preceding material node. This texture node is required.
  • Name Derived: From the latitude/longitude boundary of the DEM. Rename if you like.
  • Lat: [46.00 to 47.00] Long: [-122.00 to -121.00]
  • node is: mesh node
  • This mesh node and its construction history implement the preview mesh geometry and options system. This mesh node is linked to the group node named Palette. Obviously this node is required if you want geometry!
  • Name Derived: From the latitude/longitude boundary of the DEM. Rename if you like.
  • ExportOptionsLayer
  • node is: modifier node
  • This modifier node implements export options for terrain derived from this preview mesh. This modifier is required.
  • Name Derived: This is a modifier node but the word "layer" is used in the name to help people familiar with layer-based architectures.
  • OrthoImageryOptionsLayer
  • node is: modifier node
  • This modifier node links the preview mesh to GEOTIFF ortho-imagery on the hard disk and allows you to specify the size of the preview texture. The modifier named DynamicTextureLayer references this modifier and uses the information to perform automatic texture generation. This modifier is required.
  • Name Derived: This is a modifier node but the word "layer" is used in the name to help people familiar with layer-based architectures.
  • GeometryLayer
  • node is: modifier node
  • This modifier creates the polygonal geometry used to render the preview mesh and is linked to the material node in the palette group. This modifier is required.
  • Name Derived: This is a modifier node but the word "layer" is used in the name to help people familiar with layer-based architectures.
  • ElevationLayer
  • node is: modifier node
  • This modifier displaces the polygonal geometry and is linked to a bitmap on the hard disk. [ This is a specially packed bitmap; it doesn't "look" correct and isn't usable in an image editor. ] The displacement parameters are derived from the DEM or GEOTIFF from which the preview mesh is derived. This modifier is required.
  • Name Derived: This is a modifier node but the word "layer" is used in the name to help people familiar with layer-based architectures.
  • ProjectionLayer
  • node is: modifier node
  • This modifier projects the geometry from worldspace to the projected coordinate space, in this case Universal Transverse Mercator.
  • Name Derived: This is a modifier node but the word "layer" is used in the name to help people familiar with layer-based architectures.
  • DynamicTextureLayer
  • node is: modifier node
  • This modifier generates the preview mesh texture map by looking at the texture directory settings in the ortho-imagery modifier. This modifier is required.
  • Name Derived: This is a modifier node but the word "layer" is used in the name to help people familiar with layer-based architectures.
  • CalculateLightingLayer
  • node is: modifier node
  • This modifier generates lighting for the entire mesh. This modifier is required if you wish to work with a shaded mesh.
  • Name Derived: This is a modifier node but the word "layer" is used in the name to help people familiar with layer-based architectures.

Derivatives

This preview mesh node-set is a visual proxy for a dialog box or stack of layers. A paged terrain database is derived from the preview mesh node-set. The term derived means that a result is obtained and in this case the result is a paged terrain database.

Since Scenome uses a node-based architecture, terrain must be derived from the preview mesh node-set. The nodes have parameters that control the output of, or derivative of, the interaction between the preview mesh node-set and the Create Terrain command.

ExportOptionsLayer

Let's examine the ExportOptionsLayer and go over its key parameters.

  1. Return to Scenome and examine the hierarchy.
  2. Double click the modifier named ExportOptionsLayer.
  3. This displays modifier properties in the property editor.
  4. Scroll down and find the Output Rectangle Tessellation X/Y parameter.
    This parameter is set to 16. This means that meshes in the output terrain are created with 16×16 points.
  5. Scroll down and find the Place New Nodes Here parameter.
    The parameter is set to \Scene\Master\yakima-w. This refers to the location in the scene graph in which the paged terrain database is generated. If you examine the hierarchy you'll see the group node named Scene already exists but that group nodes named Master and yakima-w do not exist. Don't worry about this; Scenome creates these groups if they do not already exist.
  6. Scroll down and find the Export To This Directory parameter.
    The parameter is set to .\yakima-w. This means export terrain to a sub-directory of the current directory. This sub-directory is named yakima-w. A paged terrain database is composed of many individual box files; the box files are placed in this directory.
  7. Scroll down and find the Create This Many Levels-Of-Detail parameter.
    The parameter is set to 3. This means create three levels-of-detail for each tile. Notice the simplification levels for each. This tells Scenome how much to reduce each mesh. You can set these numbers to whatever you want but if you increase the number of levels-of-detail you must double click the ExportOptionsModifier again.

OrthoImageryOptionsLayer

Let's examine the OrthoImageryOptionsLayer and go over its key parameters. The term ortho-imagery refers to raster imagery acquired [usually] via aircraft or satellite. Such imagery is often skewed because of the camera angle during acquisition and must undergo a process called ortho-rectification. This is where the term "ortho" originates in this context.

  1. Double click the modifier named OrthoImageryOptionsLayer.
  2. This displays modifier properties in the property editor.
  3. Scroll down and find the Texture Settings For This Mesh parameter.
    The Use Preview Imagery parameter is set to No. This means the DynamicTextureLayer won't generate any textures. The Set Imagery Directory parameter is set to .\LOW_RESOLUTION_PROCESSED_IMAGERY. The DynamicTextureLayer looks in this sub-directory for GEOTIFF imagery and Scenome-compatible metadata. The texture width and height parameters are set to 1024 which is a decent size for a preview texture. These parameters affect the preview mesh; not the output.
  4. Scroll down and find the Texture Settings For Terrain Created From This Preview Mesh parameter.
    The Set Imagery Directory parameter is set to .\HIGH_RESOLUTION_PROCESSED_IMAGERY. This setting is copied into the output terrain. Scenome provides the option of using high and low resolution imagery directories. If you only have high resolution imagery, set the both directory values to the directory containing the high resolution GEOTIFF imagery.

GeometryLayer

Let's examine the GeometryLayer and go over its key parameters.

  1. Double click the modifier named GeometryLayer: 8x8.
  2. This displays modifier properties in the property editor.
  3. Scroll down and find the Rectangle parameter.
    The Minimum X/Y and Maximum X/Y parameters are set to represent the latitude and longitude values of the terrain. These values are derived from the latitude/longitude range of the DEM or GEOTIFF elevation imagery.
  4. Examine the Material parameter.
    This parameter links the modifier to the material node in the group node named Palette.
  5. Examine the X/Y Resolution parameterz.
    Terrain databases are built from tiles. These parameters, currently set to 8, determine the number of tiles in the output terrain database. This preview mesh produces 64 tiles for the geocell. If you use three levels-of-detail, the total number of tiles produced is 192. Right now with these parameters set to 8, the output tiles will cover 7.5 minutes of arc. This is a fancy way of saying the preview mesh produces 7.5 minute tiles.
  6. Set X Resolution to 4.
  7. Set Y Resolution to 4.
  8. Examine the worksheet: This is a picture of the worksheet.
    The preview mesh changes immediately. This full-geocell preview mesh now is configured to produce 15 minute tiles.

ElevationLayer

Let's examine the ElevationLayer and go over its key parameters.

  1. Double click the modifier named ElevationLayer.
  2. This displays modifier properties in the property editor.
  3. Examine the Translation parameter.
    This parameter defines the total translation from sea level of the vertices.
  4. Examine the Displacement File parameter.
    This parameter links this modifier a bitmap on the hard disk. This is a specially-packed bitmap that is not usable in an image editor.
  5. Examine the Starting Corner X/Y parameters.
    These parameters define the starting point of the displacement relative to the pixels in the displacement map. Since this displacement map covers the entire mesh, 0 is used to set the starting position.
  6. Examine the Displacement Width/Length parameters.
    These parameters define the ending point of the displacement relative to the pixels in the displacement map. Since this displacement map covers the entire mesh, 1201 is used to set the ending position. However you can use the starting x/y and width/length parameters to specify that a mesh is displaced by a specific, square or rectangular region of a displacement map.
  7. The remaining parameters are used by Scenome to manage and homogenize displacement across multiple meshes and multiple displacement maps. Do not alter these parameters.

GeographicProjectionLayer

Let's examine the GeographicProjectionLayer and go over its key parameters. The GeographicProjectionLayer is currently set to Universal Transverse Mercator projection. The property sheet only displays options relevant to the current projection.

Earlier you examined the properties of the GeometryLayer. The retangle boundaries in worldspace were from -122y to -121y and from 46x to 47x. This means the geometry layer is actually a very small rectangle sheet in worldspace. The GeographicProjectionLayer transforms the vertices in the GeometryLayer into Universal Transverse Mercator coordinates better known as "easting" and "northing" values. These often have huge ranges.

  1. Double click the modifier named GeographicProjectionLayer.
  2. This displays modifier properties in the property editor.
  3. Examine the Projection parameter.
    This parameter defines the projection; in this case Universal Transverse Mercator.
  4. Examine the Datum parameter.
    This parameter defines the datum; in this case WGS84.
  5. Examine the UTM Zone parameter.
    This parameter defines the UTM projection zone. It is automatically set by Scenome and should not be altered unless you know what you're doing.
  6. You can alter the projection parameter as you see fit but should only do so if you know what you are doing and why.
  7. The remaining modifiers have no editable parameters.

Build The Paged Terrain

The paged terrain database is derived from the preview mesh node-set by the Create Terrain command. Let's build the terrain.

  1. Examine the hierarchy.
  2. Right click over the mesh node named Lat: [46.00 to 47.00] Long: [-122.00 to -121.00] and select Create Terrain from the listed options.
  3. This hides the preview mesh container group while Scenome builds the paged terrain database as a set of files on the hard disk.
  4. Examine the worksheet: This is a picture of the worksheet.
    From this vantage point only the lowest level-of-detail is visible.
  5. Examine the hierarchy. This is a picture of the hierarchy.
    Scenome has added a group node named Master.
  6. Left click the + to the left of the group node named Master and continue to open groups until reach a few link nodes. This is a picture of the hierarchy.
    This is the paged terrain database. The link nodes point to files on the hard disk. And where might those files be? Remember earlier when you examined the ExportOptionsLayer and saw the Export To This Directory parameter? This parameter specified a sub-directory of the current directory named yakima-w.
  7. You can explore the database in Scenome. You will notice occasional paging drop outs while Scenome loads a parametric database and iterates the mesh construction history of the tile therein. All mesh generation, displacement, projection, simplification, texture generation, and lighting is performed on the fly.

Build The Paged Terrain Again

The purpose of a preview mesh is to provide a visual, configurable object from which you can derive terrain. The first iteration of this database had 4×4 tiles. However this is very easy to change.

  1. Examine the hierarchy.
  2. Right click over the group node named Master and select Delete from the listed options.
  3. The paged terrain database disappears.
  4. The preview is still hidden; don't worry about this.
  5. Right click over the group node named ImportResults and select Toggle Visible from the listed options.
  6. Right click over the modifier named GeometryLayer and select Tessellation: 8 from the listed options.
  7. Right click over the mesh node named Lat: [46.00 to 47.00] Long: [-122.00 to -121.00] and select Create Terrain from the listed options.
  8. Scenome builds the paged terrain database. with 4 times as many tiles. This is a picture of the worksheet.
    In this case the terrain is composed of 64 × 7.5 minute tiles per level-of-detail.

Examine Files On The Hard Disk

Let's examine the files on the hard disk.

  1. Open an Explorer window to \EXERCISES\EXAMINE_TERRAIN. This is a picture of the Windows Explorer.
    This directory contains all the preview mesh and paged terrain resources.
    • HIGH_RESOLUTION_PROCESSED_IMAGERY. Currently empty but could contain GEOTIFFS.
    • LOW_RESOLUTION_PROCESSED_IMAGERY. Currently empty but could contain GEOTIFFS.
    • TEMPORARY_ELEVATION. Contains the preview mesh displacement map.
    • TEMPORARY_ELEVATION. Contains the preview mesh texture map.
    • YAKIMA-W. Contains the paged terrain database.
    • EXAMINE_TERRAIN.BOX. The master file containing preview mesh and links to the paged terrain database.
    • YAKIMA-W.DEM. The original elevation imagery.
  2. Double click the YAKIMA-W directory.
  3. Double click the OUTPUT_MESHES directory. This is a picture of the Windows Explorer.
    This directory contains all the BOX files for the paged terrain database. There are three files for each tile, one for each level-of-detail. The place name and address of each tile is included in the file name.
  4. Move up two directories to \EXERCISES\EXAMINE_TERRAIN.
  5. CAREFUL! Delete the YAKIMA-W directory. Don't feel bad; Scenome doesn't mind.
  6. Return to Scenome and delete the group node named Master.
  7. Right click over the group node named ImportResults and select Toggle Visible from the listed options.
  8. Feel free to experiment. That concludes this exercise.