Dan Connors wrote:
A cell phone provider wants to install a cell tower in our neighborhood along
a protected ridgeline. I am working with some of the neighbors to see what
options our town has to regulate the location of the tower. I have been
trying to learn the GRASS system and volunteered to produce a map that will
show from where the proposed tower will be seen. I know the proposed
location (lat/long) and height of the tower.
I have been running some of the examples in the GRASS book (Open Source
GIS:AGrass GIS Approach, 3rd Edition) for line-of-sight calculations (eg,
page 152) and can get the examples to work for the NC sample data and the
spearfish data.
I downloaded elevation data from the USGS (1/3 arc second resolution), but I
can't get r.los to work on this data because it is lat/long based and r.los
requires XY data. I see there is an add-on module, r.viewshed which can
take lat/long coordinates as input. I guess I could also re-project the
elevation data.
Can someone suggest what map data, what projection, and which module (r.los
or r.viewshed) I should use? My goal is to produce a map like that on page
152 showing the area in my neighborhood. I think I understand the basic
concepts but I need some guidance to pull the right pieces together.
You'll probably want to choose whatever rectangular projection is used
in your state. Or alternatively just go with UTM and the zone relevant
to where you are.
The steps will be more or less:
- in the WGS84 location where you've input the USGS elevation data, set
the region to your town/neighborhood with g.region.
- get this region as a vector rectangle with v.in.region
- Close GRASS and restart, but this time create a new LOCATION based on
the CRS that you choose. I find it easiest to check for the EPSG code at
spatialreference.org and use that to create the LOCATION.
- In the new LOCATION use v.proj to project the rectangle of the
neighborhood region from the previous WGS84 LonLat LOCATION into this
new LOCATION
- Set the current region to that rectangle with g.region vect=...
- Now project the USGS DEM from the Lon-Lat LOCATION to your projected
CRS with r.proj
- You'll also have to get the X-Y coords of the tower into the new
projection. The cs2cs utility can do that. Something like this:
cs2cs +init=epsg:4326 +to +init=epsg:2039 << EOF
> 35d10'30.0" 30d30'45.0"
> EOF
216623.71 491384.93 -19.90
On the first line you'll enter the EPSG code for the CRS you chose
earlier.. The output should be the X-Y coords in the new CRS.
- Now you're ready for r.los in the new LOCATION....
Good luck...
Thank you for your help.
Dan
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