Week 4 - AppsGIS - Visibility Analysis

This week we worked on visibility analysis, using the Viewshed and Line-of-Sight tools. We worked with 4 different scenarios: viewshed looking at tower placement, security camera placement via viewshed, line of sight among summits, and and visibility of portions of Yellowstone State Park from roads.

For the security camera analysis, we worked with a raster that showed the finish line for the Boston Marathon, and were tasked with adding more cameras that could see the finish line. The view for the given camera was first for a 360 degree view at ground level. This is not the case of a typical camera, and so was later edited to account for it being on the side of a building (100 feet high) and a 90 degree view.

Figure 1. Visibility of camera near the finish line of Boston Marathon.
This is based off of 360 degree view of the camera at ground level.

The task for this portion of the assignment was to place two new cameras that would better cover the finish line. We had to place the cameras, adjust their horizontal viewing angle, and their vertical height. For the two cameras, one  was close to the finish line (Camera 2) and one on the opposite side of the finish line from the first camera (Camera 3). Camera 2 was placed in a building to the north of the finish line, on the north side of the road. The vertical offset for this camera was 75 feet, determined by a digital elevation model that included buildings. The viewing angle for Camera 2 was set to 90 - 180 degrees. This part took quite a bit of tweaking, as the degrees were not as expected and it took a while to get them right. I still am not sure why this was the case. Camera 3 had a viewing angle of 180 - 270 degrees, and was as expected visually. This camera was set to a 100 foot vertical offset, and was located about half a block west from the finish line. To show the overlap of the viewsheds, they were ranked by number of cameras that could see each cell, as shown below:

Figure 3. Overlap of viewsheds for cameras placed near the Boston Marathon finish line. Dark blue represents areas that are visible from all three cameras.

I was pleased with how this analysis came out, as the area around the finish line is quite visible. A way to improve this analysis, in my opinion, would be by ranking the distance from the camera as well. A camera does not see as well far away as it does close up, and this should be taken into consideration. I worked with closed circuit television (CCTV) monitoring, and have seen this first hand. Visibility analysis is clearly a tool that can be used in a multitude of applications, and it was neat to see how my other classmates felt it could be used. That is definitely a benefit of this class, that we all have different backgrounds, so see different "big pictures".