Lab 4 - Visibility Analysis

This week in GIS Applications we learned how to complete viewshed and line-of-sight analysis. This particular blog post will focus on one very small part of our lab, which is a visibility analysis of hypothetical street cameras at the finish line of the Boston Marathon.

Visibility analysis showing the viewshed of street cameras.

The screenshot above shows three hypothetical street cameras placed around the finish line for the Boston Marathon. The yellow circle represents my area of concern. The varying colors emanating from the cameras represent the portions of the street that area visible... unfortunately I did not include a key in my screenshot. If the key were there it would should that the lightest red color means that only 1 camera has a view of the street, the medium red means 2 cameras share that view of the street, and the darkest red means that all 3 cameras show that view of the street.

I used the following settings for the cameras when running the visibility analysis: all cameras were set to an offset height of 100 ft. The camera angles were all set to 45 degrees for the start and 135 degrees for the end. My first camera had been placed for me at the west end of the street, so to get the best coverage I placed another camera on the north side of the street by the finish line. My third camera was placed on the south side of the street east of the finish line.


I suppose that in order to better mirror reality (are all street cameras placed on streets with the exact same viewing angle?) one might need to run this analysis multiple times (so once for all cameras that have a viewing angle of 0 - 90 degrees, another analysis for those that have viewing angles of 45 - 135 degrees, etc.). Unfortunately I'm not sure how to successfully combine the results of all these viewing angle options - but I suspect it might ultimately involve some map algebra.