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TerraScan User Guide

Navigation: Tool Reference > TerraScan Toolbox > Roads and Railroads > Road toolbox

Draw Sight Distances

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Draw Sight Distances

r_draw_sight_distancesDraw Sight Distances tool determines how far a viewer sees along a road, railroad, or other corridor, and produces labels for sight distances. It’s basically a tool for line-of-sight analysis based on point clouds.

The path of the viewer along the corridor is defined by a line element. It should run along a lane of the road or a rail track at the elevation of the ground. It can be produced, for example, by drawing the trajectory line into the CAD file and draping it to the ground points using the Drape Linear Element tool. The viewer height is defined with a constant value in the tool’s settings.

The target positions for the line-of-sight analysis are also defined by a line element draped on the ground elevation. The target line can be the same element as the viewer line or another line element that is a little bit longer than the viewer line. The viewing angle which determines the area for potential obstacle search is defined as a constant value in the tool’s settings.

Potential obstacles for the viewer are represented in the point cloud. The points should be classified into a ground class by using preferably the Hard surface and/or Ground classification routines and above-ground classes. To get a reliable result from the line-of-sight analysis, any points below the ground, from moving objects, and noise above the road surface should be classified into separate classes. These classes can be excluded from the process.

The process checks if there is any point in the point cloud close to a straight line from a viewer position to a target position. If there is a point, the closest point to the viewer position determines the sight distance.

There are rules and regulations for required sight distances along a road. The distances mainly depend on the speed allowance and vary from country to country. There are different sight distance requirements for safely stopping a car or for safely overtaking another car. Example: For safely stopping a car, a viewer with a height of 1.10 m above lane center and a speed of 80 km/h must see a target of 0.40 m above the road surface in a distance of 120 m. For safely overtaking a car, the same viewer must see a target of 0.60 m above the road surface in a distance of 320 m. The viewer path needs to be cut into separate line elements according to speed limits in order to do a precise sight distance analysis.

Draw Sight Distances tool can run on loaded points as well as on TerraScan project points. It creates text elements as labels for sight distances. In addition, it can draw line elements for short sight distances into the CAD file. These line element can then be used to classify points close to them using the By centerline classification routine. The classification helps to identify obstacles in the point cloud.

To draw sight distances:

1. Create a line element along the lane centerline as viewer traveling path and (optional) another line element as target path.

2. Drape the line element(s) to the ground on the road surface.

3. (Optional) Load points into TerraScan if you want to run the tool on loaded points.

4. Select the line element that defines the viewer traveling path.

5. Select Draw Sight Distances tool.

This opens the Draw sight distances dialog:

draw_sight_distances

6. Define settings an click OK.

This starts the sight distance analysis process. The size of the text elements is determined by the active text size settings in the CAD file. The color, line weight, and line style of lines for short distances are determined by active symbology settings in the CAD file.

SETTING

EFFECT

Use

Laser points used for the sight distance analysis process:

Loaded points - points loaded into TerraScan.

Active project - points referenced by the active TerraScan project. Not UAV

Class

Point classes that are included in the sight analysis. This should include all points on potential obstacles. The list contains the active classes in TerraScan.

_select_classes

Opens the Select classes dialog which contains the list of active classes in TerraScan. You can select multiple source classes from the list that are then used in the Class field.

Tolerance

Radius around a straight line between viewer and target position within which a laser point may be considered a sight obstacle.

Viewer height

Height of the viewer above the viewer path element.

Viewer step

Distance between locations along the viewer path element where the software analyzes the sight of the viewer.

Target level

CAD file level on which the line element is drawn that defines the target path.

Target height

Height of a target object above the target path element.

Target step

Distance between locations along the target path element where the software analyzes the sight towards a target object.

Maximum distance

Maximum distances from the viewer considered in the sight analysis.

Maximum angle

Angle of sight forward from the viewer. Defines the area that is analyzed regarding sight obstacles.

Short distance

Defines the maximum value of a critical sight distance. Sight distances smaller or equal to the given value can be labeled with a different color in order to highlight the locations.

Label sight distances

If on, text elements are drawn into the CAD file that label the sight distance at each viewer position.

Level

Level on which sight distance labels are drawn.

Accuracy

Accuracy of sight distance labels. Values are rounded to the given accuracy, e.g. to the closest 5 m value.

Short color

Color of short sight distance labels. Applied to all distances smaller or equal to the given Short distance value.

Long color

Color of sight distance labels if the distance is longer than the given Short distance value.

No obstruction label

Label of viewer positions for which no obstruction is found.

Draw lines for short distances

If on, lines are drawn from viewer to target positions if the distance is smaller or equal to the given Short distance value.

Level

Level on which lines for short distances are drawn.

You can undo the creation of sight distance labels and lines by using the Undo command of the CAD platform.

TerraScan User Guide   01.01.2024   © 2024 Terrasolid Ltd