STM Display

The display of an STM is controlled through various options that can be set in the

Scalable Terrain Model dialog or the Element Information dialog.

View Density

For optimal performance, the STM display engine takes into account the

following:

• the resolution of the computer screen,

• the various resolution representations that were generated during the

creation of the STM,

• and, if applicable, the perspective setting of the MicroStation view.

The density of points displayed in a shaded, or non-shaded view is a value

between 10 and 100. This value can be set in the Element Information dialog, or

the Scalable Terrain Model dialog.

A value of 100 will result in a display of approximately one point per screen pixel.

And a value of 10 will result in a display density that is approximately 4000 times

fewer points than the highest resolution density.

The following image shows the difference between a value of 100 and a value of10 for Non Shaded View Density.

Top: Non Shaded View Density set to 100Bottom: Non Shaded View Density set to 10.

The same area is shown to the right of the dialogs. Notice the change in triangle density.

The same view density setting is available for shaded views. In that case, therendered surfaced may appear smoother when the value is set to 100.

Edge Method

How the edge of the STM is displayed is determined by the Edge Method which islocated in the Element Information dialog.

The options for the Edge Method are:

None - The edge is determined by all calculated triangles and may include slivers.

Edge Method set to None showing a typical edge sliver.

Slivers - Depending upon the dataset, slivers can occur along the edges of the

STM. These long narrow polygons typically don’t impact the shape of resultingsurface. Setting this option will turn off the slivers along the STM edge.

Max Triangle Length - Sets the maximum length allowed for a triangle that is usedfor the STM edge. When this option is selected, a field to enter the length isprovided. Maximum length settings can have a dramatic effect on the edge asshown below.

Left: Maximum length set to 25.Center: Maximum length set to 50.Right: Maximum length set to 75.

Display Modes

A scalable terrain model has a number of display modes which can be toggled onor off from icons in the Scalable Terrain Model dialog or via the ElementInformation dialog.

Options associated with each display mode are set in the Calculated FeaturesDisplay pane of the Element Information dialog.

Triangles

When the display mode Triangles is enabled, the STM is displayed as aTriangulated Irregular Network (TIN). The display of the TIN changes dynamicallyas the view zoom scale changes. The symbology and view shading mode are set inthe General pane of the Element Information dialog.

Display - Toggles the display of the triangles. This can also be set in the ScalableTerrain Model dialog.

Level - Specifies the level for the triangles.

Colour - Specifies the color of the triangles.

Line Style - Specifies the line style of the triangles.

Weight - Specifies the weight of the triangles.

Transparency - Sets the transparency of the triangles.

Thematic Display Style - Specifies the display style to use for the triangles. Whenthe option is set to From View, the display style will be the same as that of theview. The remaining options are the same as the available view display styles. TheSTM shading functionality works on the selected STM and is a global setting. Itmay be different from the view setting allowing for a more customized display.You may need to un-select the STM file in the dialog to correctly see the selectedshading.

The following image shows an STM in Thematic - Height display.

The Material pane, in the Element Information dialog, defines materials attachedto the STM and can be used for enhanced realism.

Contours

Contours can be enabled in the Scalable Terrain Model dialog and customized inthe Element Information dialog.

Max Slope Option - When set to Ignore Max Slopes, filtering of contours is basedon the Max Slope Value.

Max Slope Value - A decimal value indicating the maximum slope to be displayed.Setting this prevents the display of contour lines in steep areas. Slope defines theincline of a surface from the horizontal and is expressed in degrees.

The slope is displayed in a pop-up balloon when the STM is displayed as trianglesand when the view display mode is set to Thematic - Slope.

Left: An STM displayed as triangles showing slope value.Right: Same area displayed in the Thematic- Slope style.

Contour Label Precision - Defines the number of decimal places for the contourlabels.

Smoothing Factor - This is a number between 1 and 10 that represents asmoothing factor. A value of 10 is the smoothest. These values are only appliedwhen a smoothing option is selected.

Smoothing - Select from the following options:• None - No smoothing will be applied to the contours.• Spline - Creates smooth contours• Spline without overlap - Produces smooth contours that are unlikely tooverlap. Processing may be slower.• Vertex

Major Interval - The distance in master units between major contour intervals.

Minor Interval - The distance in master units between minor contour intervals.Expanding the Contours node provides access to customize settings for the majorand minor contours.

Expanding the Contours node provides access to customize settings for the major

and minor contours.

Depending upon the source data, contours may generate with loops. Closeexamination of loops will reveal that they contain multiple triangles at the sameelevation. The generated contour lines bound these flat ares which then results inloops.

Draped Rasters

If there are images available for the area covered by the STM, they can be drapedonto the generated surface. To drape images, the following conditions must bemet:

• Attached images must be parallel to the top view.• Attached images must overlap the STM.• Attached images must be displayed in the active view.

The Raster Draping dialog is accessed from the Set Draping item found in the Editmenu of the Scalable Terrain Model dialog, or from the icon bar.

The Raster Draping dialog has two panes. The left side shows the attached imagesthat are available for draping, and the right side shows the attached STMs. Selectthe rasters to be draped on the left side and move them to the selected STM onthe right. Moving an image will detach it from the Raster Manager. Copying theimage will drape it on the selected STM but still be available in the RasterManager.

To view the draped images, enable Display Draped Rasters from the ElementInformation dialog, or from the Scalable Terrain Model dialog.

The view shading mode should be Smooth to view the draped terrain.

Top: Triangles show a depression in the terrain.Center: View shading set to smooth clearly illustrates the depression.

Bottom: Draped images reveals a quarry.

Terrain Model

A terrain model is recognized as a MicroStation element type as of MicroStation

V8i (SELECTseries 3). Like an STM, a terrain model (TM) is a set of triangles

mathematically computed from point data collected on the surface being

modeled. They are used to model highly irregular surfaces, particularly the

surface of the earth. Terrain models are also referred to as digital terrain models

(DTMs), triangulated irregular networks (TINs), or triangulated surfaces.

The notable difference between Descartes STM and MicroStation’s TM is the

display speed. Descartes only load the points needed for the view, while

MicroStation loads every single point.

When dealing with large numbers of points and breaklines, it will be inefficient to

work with a terrain model element. In this case, use the source data to create a

scalable terrain element.

Exporting

An STM can be exported to a TM by selecting File > Export to STM to TM from the

Scalable Terrain Dialog. Once exported, the STM will be detached and a new TM is

created.

The goal of this function is to improve the interoperability between the STM and

the TM element by allowing users to perform analysis such as volume calculations

on a TM element.

Since the data of a TM element is kept in memory, the area that can be extracted

is limited by the number of STMs terrain data available in that area. If the area

contains too much terrain data, a warning will be displayed.

Once created, MicroStation’s Label Terrain Contours and Label Terrain Spots canbe used to annotate the terrain element. These tools are found in MicroStation’sTerrain Model toolbox.

The Element Information dialog can be used to adjust the display settings of theterrain.

For details on tool usage, please refer to MicroStation’s documentation.

Extracting

Since STMs typically cover extremely large geographical areas, it may bepreferable to extract only those areas that are of interest. Specific areas of an STMcan be exported to a TM by selecting Extract a TM Element from STM from theEdit menu of the Scalable Terrain Model dialog. The resolution for this operationis 1:1.

Tool settings for Extract a TM Element from STM are described as follows:

Area - Sets the method to define the area that will be exported. Options are:Block, Oriented Block, Element, Shape and View.

Boundary - Sets the boundary which is defined by:

• Area - if the shape presents concave sections, the shape outline will beclipped to extract the TM.• Convex Hull: if the shape presents concave sections, the extracted TMwill fill the concave areas to generate a convex shape.

The following illustration describes a convex hull which is the smallest possibleshape that still contains all of the points within the selected area.

The area being selected is shown in the dashed black block. The points the datasetare red. The blue line that bounds the points that lie inside the selected area is theconvex hull.

When determining the area, if the maximum number of points is attained, awarning will display.

The extract operation applies to all STMs located in the selected region, but willgenerate a single TM.

The properties of the originating STM are used to generate the TM. If more than

one STM is used in the extract operation, a dialog will display allowing to select

which STM’s properties to use.

Viewshed Analysis

A viewshed is the area that is visible from a specific location based on elevationvalues.

Descartes Viewshed Analysis determines what part of a terrain is visible from aspecified location or path. For example, this analysis can answer the followingtypes of questions:

• How much of this forest clear cut is visible from the road?• Can the gravel pit be seen from this location?• Can a communication tower be seen from this point?• What is the best location for a fire observation station?• What is the impact of building a 30 story building on this site?

The result of the viewshed analysis is a raster grid where the value of each pixelrepresents the number of times pixel area was visible from the viewers positionduring the analysis.

The view position can be either static or along a path. For static positions, thepixel value can only be one of two results: visible or not visible from the selectedlocation.

Viewshed analysis based on a static point (red). White pixels represent visible areas, black pixels represent hidden areas.

For analysis along a path, the pixel value represents the number of times thatlocation is visible from an observation point. Calculations are performed atobservation points along the path of the selected element at specifiedincrements.

Viewshed analysis along a path (green linestring).Each pixel represents the number of times that location is visible from an observation point along the path.

Red pixels are visible, blue pixels are hidden.

Only one output file format supported, which is a geo-referenced iTIFF. This

ensures that the raster grid is positioned over the source area.

The Viewshed Analysis dialog provides the following settings:

Area - Defines the area to be processed. An STM is very large and in many cases

areas away from the selected viewpoint do not need to be processed. Select from

one of the following options: Block, Oriented Block, Element, Shape or View. Use

the selection tool to identify the appropriate area or select the element or view.

To improve performance, consider using a shape to precisely define the region to

analyze. This eliminates unnecessary processing when defining the area by block

or by view.

View Position - Describes the viewer’s position and provides the following

settings:

Method - Defines the method to use which is one of the following:

• Static Position - Enter the XYZ positions can be keyed-in or be defined with the

selection tool.

• Along Element - Enter the increment distance along the path to define the

observation points from which to calculate results. A smaller increment will

increase processing time.

Elevation - Specifies the elevation to use. This can be a selected element, the

height of the STM at a point, a specified height above the STM, or a user defined

elevation.

Output - Specifies the output file parameters.

Pixel Size - The size of the output pixel in the resulting grid file. Small pixel valueswill significantly increase processing time.

Grid File Name - The name of the resulting grid file.

Viewshed Workflow

Viewshed Analysis is performed from the top view. When using a static position,identify the location with the selection tool. If using Along Path, use the selectiontool to identify a linear element. Then identify which end of the selected elementis the starting point.

After setting the viewshed range and appropriate parameters select Run andidentify the view to be used to calculate the viewshed. The resulting analysis willbe produced in the specified grid file which can be attached for visualization.

Raster grid files differ from raster images in that each pixel represents an intensity

value. The display of the values can be selected by the Thematic Display optionfrom the right click menu.

Inspection of the results indicates portions of the playing field that are not visiblefrom the selected viewpoint. For a soccer player, this may mean that the ball isnot visible from this particular location. Since it’s assumed that the field should bea flat space, it would be recommended to explore why there are hidden areas onthe field. The following are a few suggestions:

• Explore and evaluate the STM surface for obvious elevation changes. Itappears there is an elevation change as indicated by the arrows.

• Display the STM using the Thematic Height display mode. Adjust the elevationrange as needed.

• Since the source data for the STM is the point cloud, set the display mode toElevation and Intensity. This allows you to clearly see the changes in elevationof the points within the playing field.

These changes in elevation may be the result of noise, a rough and unevensurface texture, wear and tear of the playing field surface and so on.

• Since the STM is built using only those points classified as Ground, use the EditClassification tool to reclassify the field to another classification.

When the STM is generated from the modified point cloud file, the field is

represented as flat surface.

Regenerating the viewshed from the modified STM produces better results:

If needed, further refinements can be made with the inclusion of breaklines to

delineate the playing field from the surrounding terrain.

Configuration Variables

Draping:

STM_DEFAULT_MINIMUM_PIXEL_SIZE_FOR_DRAPING - When draping imageson the STM, Descartes creates a single tiled image over the draped area. The pixelsize of this image is defined as the smallest pixel size of all the draped rasters.However WMS does not have a defined pixel size. In some cases the WMS serverdoes not respond correctly with an appropriate pixel size. In these cases the valueof STM_DEFAULT_MINIMUM_PIXEL_SIZE_FOR_DRAPING is used to determine asuitable pixel size. It is set to 0.5 meter by default.

STM_RASTER_DRAPING_TRANSPARENCY - The transparency of the rastersdraped on the STM can be adjusted by defining the this variable. It specifies aglobal transparency that will be applied to the raster data draped on all attachedSTMs. The value for this variable can be from 0 to 100 where 0 is no transparencyand 100 is fully transparent. The default value is 0.

Animation and Rendering:

STM_PRESENTATION_QUALITY = 1 - The STM display is optimized for interactiveoperation. However, when recording an animation project, the resulting qualitycan be less than optimal, especially when there are many breaklines. To improvethe quality of the resulting animation, define the variable above. The interactiveoperation will be slower but the rendering results will be improved.

Exporting to a Terrain Model:

STM_DOWNSAMPLING_PREFSIZE - Controls the size in MB of the exportedterrain element. The default is 5. A higher value may result in a TM that containsmore triangles.