Visibility Analysis Tools

The Visibility Analysis tools display surfaces and structures that are visible and hidden from an observer. The Viewshed tool shows visibility from a camera-like observer. With the View Dome tool, you can visualize visible and hidden areas from an omnidirectional observer. Finally, the View Corridor tool creates a protected view where any scenario building visible in the corridor is colored.

By using these tools, you can create Analyses objects that can be saved in your CityEngine scene. To learn more about Analyses objects in the Scene Editor and Inspector, see Manage Analyses objects

The Visibility Analysis tools snap to buildings and terrains to facilitate the positioning of the observer point and the point of interest.

Viewshed Tool

Use the Viewshed tool when you want to determine the visible area from an observer point to a point of interest. The Viewshed colors areas that are visible (by default in green) or occluded (by default in red) from the observer. The Viewshed object you created can then be managed in the Scene Editor.

Create a Viewshed

To create a Viewshed, do the following:

  1. Click a point in the viewport to create an observer point. This starts the Viewshed tool and a line dynamically displays the Viewshed as you move it to set the point of interest.
  2. Click again to anchor the point of interest in the Viewshed.

Once created, the Viewshed is automatically selected, and you can directly adjust its properties, such as the angles of view and view distance in the Viewport using handles or in the Inspector using input fields.

Adjust the Viewshed in the Inspector

The Viewshed object you created is added to the Scene Editor and you can modify its properties in the Inspector. The Colorize Scene property allows you to choose whether you want to display the colorized visible or hidden areas in viewports. The preview shows you the view from the observer point with the current properties, enabling an intuitive placement of the Viewshed.

Visibility by layer

Inspector displays visibility statistics about the current Viewshed and breaks the visibility down by layer. See Visibility by layer for more detail.

Properties

You can adjust the viewshed by changing the properties below.

Properties Description
Horizontal Angle of View Horizontal angle of view, or field of view, from observer
Vertical Angle of View Vertical angle of view, or field of view, from observer
Observer Point X x coordinate of observer
Observer Point Y y coordinate of observer
Observer Point Z z coordinate of observer
Tilt Angle Vertical camera view angle from -85 to 85 degrees
Heading Angle Horizontal camera view angle from -360 to 360 degrees
View Distance Distance between observer and point of interest

Adjust the Viewshed in the Viewport

Select the Viewshed object in the Scene Editor or directly in the Viewport to start modifying it. Six orange spheres appear. Clicking and dragging one of these handles allows you to modify the observer point, the point of interest, or one of the angle of view.

View Dome

The View Dome tool allows you to see the visibility from a given point in a 360 degrees view. The View Dome colors areas that are visible (by default in green) or occluded (by default in red) from the observer. The View Dome object you created can then be managed in the Scene Editor.

Create a View Dome

Click on a point in the scene to set the observer point and then drag to create the View Dome. Once created, the View Dome is automatically selected, and you can directly adjust its properties, such as the view distance in the Viewport using handles or in the Inspector using input fields.

Adjust the View Dome in the Inspector

The View Dome object you created is added to the Scene Editor and you can modify its properties in the Inspector. The Colorize Scene property allows you to choose whether you want to display the colorized visible or hidden areas of the View Dome in viewports. The preview shows you the 360 degrees view (using an equirectangular projection) from the current observer point.

Visibility by layer

Inspector displays visibility statistics about the current View dome and breaks the visibility down by layer. See Visibility by layer for more detail.

Properties

You can adjust the viewshed by changing the properties below.

Properties Description
Observer Point X x coordinate of observer
Observer Point Y y coordinate of observer
Observer Point Z z coordinate of observer
View Distance The distance of from the observer to the edge of the View Dome

Adjust the View Dome in the Viewport

Select the View Dome in the Scene Editor or directly in the Viewport to start modifying it. Five orange spheres appear. Clicking and dragging one of these handles allows you to modify the observer point, the view distance.

View Corridor

View Corridors protect established view from given observer against building development obstruction. For example, there are multiple view corridors in the city of Seattle that keep the Space Needle clear of buildings. View Corridors are well known practices and accepted mechanisms to keep views of landmarks from being blocked or compromised.

View corridors are designed to analyze scenarios. It is recommended to create scenarios first before creating the view corridor objects because only buildings in a scenario are colorized by the View Corridor.

Create a View Corridor

To create a View Corridor, do the following:

  1. Click a point in the viewport to create an observer point. This starts the View Corridor tool and a line dynamically displays the View Corridor as you move it to set the point of interest.
  2. Click again to anchor the point of interest in the View Corridor.

Once created, the View Corridor is automatically selected, and you can directly adjust its properties, such as the angles of view in the Viewport using handles or in the Inspector using input fields.


All parts of scenario objects that lie in the View Corridor and are visible from the observer are colored with a chosen color (default is red). To see the Scenario A objects in a View Corridor you need to activate Scenario A in the viewport scenario dropdown. See scenarios for more information on scenario objects.

Adjust the View Corridor in the Inspector

The View Corridor object created is added to the Scene Editor and you can modify its properties in the Inspector. The Colorize Scene property allows you to choose whether you want to color the scenario objects that are in the View Corridor. The preview facilitates the placement of the View Corridor, and shows which active scenario objects alter the protected view. Additional properties of the View Corridor object are:

Properties Description
Horizontal Angle of View Horizontal angle of view, or field of view, from observer
Vertical Angle of View Vertical angle of view, or field of view, from observer
Observer Point X x coordinate of observer
Observer Point Y y coordinate of observer
Observer Point Z z coordinate of observer
Point of interest X x coordinate of point of interest
Point of interest Y y coordinate of point of interest
Point of interest Z z coordinate of point of interest

Adjust the View Corridor in the Viewport

Select the View Corridor object in the Scene Editor or directly in the Viewport to start modifying it. Six orange spheres appear. Clicking and dragging one of these handles allows you to modify the observer point, the point of interest, or one of the angle of view.

Visibility by layer

Inspector displays the visibility percentages each layer contributes to the total view. Furthermore, solid view angles calculated in steradians (sr) are displayed. Also, under the preview there is a horizontal bar displaying layer visibility percentages with colors that match the geometry in the preview.

The Panorama category applies to all the non-geometry areas, inculding the sky and the area below the horizon not covered by terrain.

Currently, Visibility by layer is not available for View Corridor objects.


For further analysis, you can expand a layer to see how much of it is visible or occluded within the Viewshed or View Dome. Furthermore, you get a list of layers that contribute to the occlusion of the expanded layer including percentages and sr values. In the Viewshed below, 15.7% of the Streets layer is visible and 84.3% is occluded by other layers. Additionally, you can see the Office building layer is the main occluder of the Street layer with a share of 55.3%.

Scenarios

You can compare visibility statistics between scenarios. Using the Street layer again, you can compare View Dome analysis of Development A and B. With Development A, the Office buildings layer occludes 54.3% of the Streets layer.


While with Development B, Office buildings only occlude 12.5% of Streets. See Scenarios for more information.

Manage Analyses objects

You manage the Analyses objects you create through the Scene Editor and the Inspector. The Analyses objects you create behave like other objects you create in CityEngine with the following properties:

Scene Editor

The Scene Editor automatically adds the Analyses objects you create in a new Analyses layer. You can also create new Analyses layers to designate where the Analyses objects will be created. To create a new Analyses layer, do any of the following:

Analyses objects do not belong to scenarios and will always appear in the Scene Editor.

Inspector

You can modify the Analyses Layer properties under Layer in the Inspector. In addition to the default layer properties, Analyses layers have the following properties:

Visibility Settings

You can show or hide all Analyses objects in a given viewport through the Visibility settings.

Overlapping objects in an Analyses layer

Viewshed and View Dome objects can interact with each other when they overlap. This is helpful to determine if a specific area is visible by multiple observers at the same time. You can have multiple Analyses layers with multiple objects but objects only in the same layer can interact and reflect the overlapping visualization. As you modify individual Analyses objects this will affect the colors displayed in the scene.

If Viewshed or View Dome are not in the same layer but overlap, the coloring will not be working as expected (not yellow). Therefore, if Analysis objects overlap we recommand to place them in the same layer.

View Corridors don’t interact with Viewsheds or View Domes. Therefore it is recommended to create View Corridors in a separate Analyses layer.

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