These can be vital processes, as 3D display often helps communicate ideas and visualizations more clearly than 2D display, and viewshed and line of sight can both assist when determining what is visible or accessible to targets. In a real world application this analysis could be used to check radio wave transmission, camera or radar coverage, and manage visual access to resources like mountain views or emergency assistance kiosks.
In 3D Visualization we learned different types and methods of assigning three dimensional symbology, including things like picture fill, procedural fill, and rule packages to create more detailed and unique symbols.
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| Embarcadero Park and downtown San Diego rendered in a 3D Scene with customized symbology. |
As part of the 3D Sharing class we authored a three dimensional scene that gave me the opportunity to apply some of the basics learned in 3D Visualization. This meant extruding 2D polygons based on their height for buildings, and then correcting where the buildings "sat" with the Layer 3D To Feature Class tool. This correction made several buildings in elevated terrain suddenly become visible, because they had previously been drawing "under" the elevated ground of the hill. Trees had been included as points, so I added z values with the Add Surface Information tool based on height, then used the Feature To 3D By Attribute tool to make trees a 3D feature based on their new z-axis. In order to get the trees to display properly, they had to be removed and then re-added as a preset layer, with appropriate symbology.
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| 3D map of part of Portland Oregon, with extruded trees and buildings. This was created for sharing and is also available online on My Content Page. |
In order to Publish the buildings in the scene (the only multipatch layer) I used the Create Object 3D Scene Layer Content tool and made a shareable .slpk file of the buildings layer. I attempted to move the package file directly to my ArcOnline account from Google Drive, but the .slpk file type is not one of the four filetypes that can be uploaded directly from Google. Instead I downloaded the package and uploaded it from my device. I followed the instructions for properly labelling and describing my building layer as an Item on My Content page, then published it and opened it in SceneViewer where I used Capture Slides and Daylight tools to view the 3D buildings in different lighting and saved the views as slides.
During the Viewshed Analysis we were given a scenario with light sources at two possible heights, and used the Viewshed Analysis tool to see how much of a hypothetical campground terrain would be illuminated by the lights.
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| Viewshed Analysis rasters displaying how the four lights cover the campground at heights of 3 meters (left) and 10 meters (right). The lightest shade represents coverage by only one light, while the darkest shade represents coverage by four lights. |
Since the hypothetical campground was requesting that at least half the space be covered by 3 or more lights, I used the Greater Than raster function with a Raster2 value of 2 to highlight just the areas illuminated by 3 or more lights in each of the two light height scenarios. Based on the coverage from these rasters, it was clear that the lights would need to be at a height of 10 meters (OFFSETA = 10) for at least half of the campground to be covered.
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| Boolean rasters generated from the Greater Than tool that display the area covered by at least three lights when the lights are mounted at 3 meters (left) and when the lights are mounted at 10 meters (right). The 10 meter lights illuminate at least half of the campground. |
The Line of Sight analysis centered around the use and parameters of the Line of Sight tool. We were provided with a three dimensional model of a section of Philadelphia, complete with buildings, observation points, and a parade route line. I used the Construct Sight Lines tool to create lines between the observation points and the parade route, then input those lines into the Line of Sight tool (with buildings as inputs for obstructions) to get a line feature class that was color coded based on whether the parade was visible or not along that line of sight.
However, because humans don't have eagle eye vision, I needed to limit the lines to only those that were equal or less than 1,100 ft long. This is the commonly accepted value for clear day visibility. To do this, I calculated and added the length of the lines as an attribute to the feature class with the Add Z tool, and then used Select By Attribute and Delete tool with the expression TarISVis = 0 OR where Length3D is greater than 1100. This selected and removed lines that either could not see the parade route, or required more than 1,100 ft of visibility.
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| Lines of sight from the elevated observation points that would be able to see the parade route (red) in downtown Philadelphia on a clear day. |
In the second part of the Line of Sight lesson, we explored a module that would also complete these steps, but for visibility of 600 ft, which may happen on a foggy or rainy day.
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| A view of the module, which would run the LOS analysis for the dataset with changes to the expression that will remove lines with a length greater than 600 ft. |
The module with reduced visibility returned a map with fewer lines of sight than when the LOS analysis was conducted for a clear day.
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| Fewer viable lines of sight when the visibility is reduced to just 600ft. |
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