Lab 4 - Visibility Analysis

This lab was very lengthy but we learned several new techniques around the overall theme of visibility analysis. We learned to perform viewshed and line of sight (LOS) analyses using elevation models. We worked with LIDAR data and prepared it for use in visibility analysis. We created and investigated profile graphs for LOS analysis. We also learned to adjust various parameters used in visibility analysis, such as offset and various viewing angles.

In the first part of this assignment, our objective was to perform a visibility analysis for three potential fire tower locations. We created a viewshed and an observer raster and investigated the differences. The viewshed shows areas visible from a specific observation point or points, where an observer raster shows which observer points are visible from each raster location, which is a somewhat confusing concept.

For the second part of the assignment, our objective is to create a map of visibility from the roads in Yellowstone National Park. Fortunately, the visibility raster was provided for us. It identifies areas not seen from any roads and areas seen from one or several locations on roads. After creating the map, it can be seen by qualitatively comparing the topography and visibility that the higher visibility areas coincided with either areas of higher elevation or areas very near the roads, which makes sense. My map is found below.

The third part of the assignment introduced us to LIDAR and LOS analysis. Here, we want to examine the viewshed from camera locations and place new ones for optimal coverage at the site of the Boston marathon. First, we added the LIDAR image of the area and created a DEM using the LIDAR data as the input. After adding the cameras and orthographic image of the Boston marathon site, we performed a viewshed analysis. We had to modify the offset and viewing angle to be more realistic (the default offset is “0”, which is at ground level and the default viewing angle is all angles). Determining the placement of two new cameras took some trial and error. I would try a location, run a visibility analysis, and move the camera if I didn’t like the location. I wanted to cover the street, the sidewalk areas, and the buildings immediately surrounding the finish line with three security cameras. Camera 1 is placed really well, as it views most of the length of the street, but there are several areas, mainly near sidewalks, that it misses. For Camera 2, I decided to place it at a height of 80 feet, on the corner of a building located on the northeast corner of the intersection just to the northwest of the finish line. Its facing in such a way that it covers a viewing angle of 90° to 180°, so east to south. The height of this building is approximately 180 feet, but I was concerned that placing the camera that high up would not be able to see things well at ground level, such as behind vegetation or on sidewalk areas under buildings. So I placed the camera at 80 feet, at what looks like the corner of the building. There appears to be a ledge there, so it should be able to be mounted fairly easily. Camera 2 captures the area east to south of that location, and it gets a good view of the sidewalk side of the vegetation, which is what I was having trouble with when placing it at other locations. Camera 3 is the camera placed furthest away from the finish line. It’s on the corner of a building across the intersection east-northeast of the finish line. Camera 3 is at a height of 100 feet, also on the corner of a building, covering a viewing angle from 180° to 270°, or south to west. My main purpose for placing it here is that I want to capture both intersections immediately next to the finish line, and this camera does that well as well as capturing the finish line itself. The blue areas show where its covered by one camera, green by 2 cameras, and red by all 3 cameras. All 3 cameras capture the finish line and the area immediately surrounding it. Below is a screenshot of my camera locations and visibility analysis.

The final part of this lab was a line of sight analysis using the Create Line of Sight tool in the 3D Analyst toolbar of ArcMap. This is a really neat feature that quickly gives point-to-point line of site analyses, and can work with multiple points at once. Our data contained all 15 summits and we created an LOS analysis for all at once. What this did is create a LOS path from each summit to every other summit. We then compared this LOS tool to the viewshed output for a particular summit.

I really learned a lot in this lab. I had some issues seemingly where others did, around the last couple questions of Part A. I’m still a little iffy on the differences in what the viewshed raster represents as opposed to the observer raster, and finding which summits can be seen from a specific peak was confusing as the layers did not define the peaks with a consistent ID value, so there was a lot of comparing between the two visually on that section. Overall though, I learned a lot from this lab and really enjoyed working with the various methods of creating a visibility analysis.