Module 3- Visibility Analysis- Applications in GIS

    This week’s lesson centered around 3D visualization techniques in ArcGIS as well as performing line of sight and viewshed analyses. Before working with 3D visualization there are several important core concepts to understand.

     We covered how to determine which of the 3 elevation types to utilize and how to set or change elevation type in ArcGIS Pro. The 3 elevation types are:

    - on the ground (typically used for vegetation or buildings)

                - relative to the ground (traffic cameras, subsurface features)

                -an absolute height (airplane paths, satellites)

    Other important terms are:

        -  cartographic offset, or adjusting the height of an entire layer so that the features are not obscured by others layers within the scene. In our case the houses were obscured by the trees, so we set the cartographic offset to 50 to make them visible.

        - vertical exaggeration, emphasizing vertical features on a map, particularly useful in cases where the horizontal extent is vast.

                          This image gives and examples of cartographic offset. The red dots represent houses in the  neighborhood. However, without sufficient cartographic offset some of the houses were obscured. 50 feet was sufficient to see all the houses clearly.

    We covered the process of extruding data. Extruding data from a 2D to a 3D feature can be a way to visualize more than just the literal dimensions of an object. For our exercise we extruded building using their absolute value in order to visualize the most valuable properties in a city.

For this map the yellow symbolizes residential properties, the pink represents commercial properties and the gray represents public housing. The height of the buildings isn't their actual height but instead representative of their absolute property value.

  Additionally we covered how to apply visual effects using symbology, and setting illumination properties for global and local scenes to see the effects of shadows and illumination on the scene. 

    After we covered introductory 3D concepts we performed both a line of sight analysis and a viewshed analysis. 

    The 3 main steps to performing a sight line analysis are to determine observers and targets, construct sight lines, and determine lines of sight. We used ArcGIS 3D analyst tools to complete these steps. We considered line of sight from 2 observation points along a parade route we considered only those with visibility within 600ft which left clear gaps in coverage from a security standpoint.

                        The centermost portion of the parade route was completely absent of coverage with the line of  sight analysis at 600ft.

For our viewshed analysis we assessed a proposed campground lighting system to determine what height was necessary to obtain sufficient campsite coverage.

Viewshed analysis photos assessing a proposed campground lighting system. Ideal coverage was more than 2 observers.

    

    Finally we covered how to create a site-specific 3D scene in ArcGIS Pro from 3D datasets. One important tip I took note of in this section is that when you are extruding features from 2D to 3D symbology (such as a building), one way to ensure accuracy is to extrude the features at an absolute height, and then convert the newly extruded features to multipatch features before switching the elevation type to "on the ground". Drawing at an absolute height ensures the slope of the terrain doesn't interfere with the rendering of the feature, and if you change the elevation type before converting the data to a new feature class it will not keep the features as they were drawn at an absolute height but will re-draw them at ground level. I also found it worth noting that extruding the features does not automatically make a new, shareable 3D feature class.

    Overall I feel like this exercise gave me new insight into what 3D tools and options are available to me with ArcGIS Pro.

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