Viewshed

[mattbartlett]

Hi,
Just bought the GM today - what a wonderful program. Two questions:

1) Is there a way to do an inverse of a view shed (e.g. within a 2 mile radius, where is the transmitter not visible from). The only way I can see doing this is to create the viewshed, and then create new area polygons manually in the areas that the viewshed does not cover. Hopefully there is a better way of doing this as that can get very tedious.

2) Is there anyway to import data that shows local vegetation cover when doing a viewshed? I haven't seen this data on any GIS clearinghouse. Any thoughts on this?

Thanks!
Matt

[global_mapper]

Matt,

While there is not a direct way during view shed generation to generate polygons in the areas not covered, what you could do is use the Digitizer Tool to create a range ring polygon at your desired radius covering the area of interest, then select all of the coverage polygons, right click, select the option to add the polygons as islands/holes in another area, then click in the range ring area. This will add holes to your range ring area, giving you a polygon that only covers the no-coverage areas.

If you can pull in vegetation data with elevation attributes you can use it as obstructions during the view shed calculation, but I'm not aware of any good sources of that data.

Let me know if I can be of further assistance.

Thanks,

Mike
Global Mapper Support
support@globalmapper.com