Viewshed Analysis in Global Mapper
Among Global Mapper’s many terrain analysis tools is the Viewshed Analysis function. Accessed from the Tools menu or with a button in the Analysis toolbar, Global Mapper’s Viewshed Analysis tool has been an important part of the program for many years and has undergone various improvements to expand the tool functionality.
The premise of a viewshed is similar to line of sight: from a defined location, what can be seen? A simple line of sight analysis is completed in Global Mapper using the Path Profile tool, but this operation is restricted to a single path between two points. The Viewshed tool greatly expands the extent of analysis to compute areas of visibility as opposed to lines and comprehensively determine what can be seen or reached from the origin point.
The applications for viewshed analysis are wide-ranging and include topics related to surveillance, viewpoints, signal reach from transmitter locations, and many more. A multiple-point viewshed analysis was used to determine cellular signal coverage in this Global Mapper industry showcase.
The rocky coast of Maine, the home state of Blue Marble, contains many inlets and outcroppings making it difficult for ships to maneuver. These days, advanced technology onboard vessels provide accurate positioning and sounding measurements to improve safety, but in the past captains and crews relied only on paper maps, compass positioning, and lighthouses as they approached the rocky coast.
Vessels relied on the positioning and light of lighthouses along the coast to keep them safe. Using modern GIS technology, the lighthouse network along the coast of Maine can be analyzed with Global Mapper’s Viewshed tool.
Beginning with terrain data streamed into Global Mapper via the Connect to Online Data tool and a layer representing lighthouse locations, the creation of a viewshed from the lighthouse points is simple. By selecting the lighthouse points before initiating the viewshed analysis process, Global Mapper provides the option to compute a viewshed for each selected point.
Within the Viewshed Setup, many options allow the analysis to be customized for the selected situation. In addition to specifying the lighthouse height and view radius, advanced options consider 3D vector features and identify hidden instead of visible areas. In this scenario, the option to combine viewshed layers is used to consider the overlap in lighthouse visibility along the coast.
The latest addition to Global Mapper’s viewshed tool is the creation of 3D vector mesh buffers describing the viewshed radius. Represented as spherical mesh features centered on each viewshed origin, the features show the extent of the radius which was assigned in the setup process. potential visibility from each point.
The viewshed coverage data resulting from this viewshed analysis consists of the individual layers for each transmission point, as well as a combined viewshed grid layer. This grid summarizes the overall visibility coverage by the constellation of lighthouses. As expected, the view over the ocean area is much greater than the view towards the land. The gridded format of the combined viewshed layer allows a custom shader to be applied to better identify visible and hidden areas along the coast.
Whether analyzing the view from a single point or a radio signal to a specific area, the viewshed tool in Global Mapper provides an effective way to visualize and measure the coverage area by creating both vector and raster data describing the visible or hidden areas.