**--overwrite**- Force overwrite of output files

**input**=*string*- Raster map containing elevation data
**output**=*string*- Raster map name for storing results
**coordinate**=*x,y*- Coordinate identifying the viewing location
**patt_map**=*string*- Binary (1/0) raster map to use as a mask
**obs_elev**=*float*- Height above ground of the viewing location
- Default:
*1.75* **max_dist**=*float*- Max distance from the viewing point (meters)
- Options:
*0-99999* - Default:
*1000*

To run *r.los*, the user must specify at least
an **input** map name, **output** map name, and the geographic
**coordinate**s of the user's viewing location;
any remaining parameters whose values are unspecified
will be set to their default values (see below).

The **patt_map** is the name of a binary (1/0) raster map layer in which
cells within the areas of interest are assigned the category value '1', and
all other cells are assigned the category value '0' or NULL. If this parameter is
omitted, the analysis will be performed for the whole area within a certain
distance of the viewing point inside the geographic region boundaries.

Default: assign all cells that are within the **max_dist** and within
the user's current geographic region boundaries a value of 1.

The **obs_elev** parameter defines the height of the observer (in
meters) above the viewing point's elevation.

The **max_dist** parameter is the maximum distance (in meters) from the
viewing point inside of which the line of sight analysis will be performed.
The cells outside this distance range are assigned a NULL value.

The time to complete the calculation increases dramatically with the region size. Try to keep the columns and rows under 1000.

It is advisable to use a 'pattern layer' which identifies the areas of interest in which the line of sight analysis is required. Such a measure will reduce the time taken by the program to run.

The curvature of the Earth is not taken into account for these calculations.
However, for interest's sake, a handy calculation for distance to the true horizon
is approximated by *d = sqrt(13*h)* where *h* is the height of the observer
in meters (above sea level) and *d* is the distance to the horizon in km.
This may be useful for setting the **max_dist** value.

r.los elevation.dem out=los coord=598869,4916642 obs_elev=50 max_dist=10000 r.colors los color=rules << EOF 0% blue 75 blue 80 cyan 85 yellow 90 red 100% red EOF d.his i=aspect h=los echo "symbol extra/target 25 598869 4916642 red black" | d.graph -m

*Last changed: $Date: 2007/10/31 04:06:53 $*