[GRASSLIST:3255] Slope data under a ship track.

[Gordon Keith]

I have a problem I was wondering if grass could solve, and if so the 
easiest method.

I have a bathymetry dataset I have imported into grass and generated 
slope and aspect rasters. (~20m resolution, lat long coordinate system)

I have a ship track consisting of latitude and longitude coordinates 
every 90m (0.05Nm) along the ship's track. There are a few thousand 
such intervals.

What I would like is for each interval in the ship track (start and end 
lat/lon coordinates) to know the average (or max) slope of all points 
within say 30m of the line between the two points.

My guess is that I would have to format each pair of points as a file I 
could pass to v.in.ascii, convert the vector to a raster (v.to.rast), 
use r.buffer to get the surrounding area, use the buffer as a mask 
(r.mask), and collect the statistics from the masked area 
(r.statistics), output the results of the statists (r.stats) and 
reformat the output.

Is there a tider way of doing this?

FWIW The area I'm trying to gather the statistics for is the footprint 
of a single beam echosounder over the area where an index of the bottom 
type has been calculated by integration of the echo return. This 
statistic should give some sort of measure of the quality of index 
calculated.

Regards
Gordon

-- 

Gordon Keith
Programmer/Data Analyst
Marine Acoustics
CSIRO Marine Research
http://www.marine.csiro.au

"640K ought to be enough for anybody." Bill Gates, 1981