Road slope from DGPS sites [vectors]

[James Cameron]

G'day,

I have data from my DGPS survey of a set of tracks on my farm, which
includes a series of points with altitude (ASL) as I walked along the
tracks.  I want to prepare a colour map showing the tracks in colours
according to the slope of the track in the direction of travel.  The
colours would change along a track.

This is so that I can work out which bits of the track need work.

I've moved the data into a sites file, with the ASL properly formatted
such that I can use s.whatever.to.rast to convert to a raster.  I've
then been able to spread the raster slightly before using r.slope.aspect
to generate a raster of the slope in degrees.  But of course, as you
move away from the track the numbers fall off ... 

So I think I've done it wrongly.  How should it be done?

What I get looks like this;

	0 0 0 0 0 1 2 2 3 4 4 3 2 2 1 0 0 0 0 0
	0 0 0 0 0 1 2 2 3 4 4 3 2 2 1 0 0 0 0 0
	0 0 0 0 0 1 2 2 4 5 5 4 2 2 1 0 0 0 0 0
	0 0 0 0 0 1 2 2 3 4 4 3 2 2 1 0 0 0 0 0
	0 0 0 0 0 1 2 2 3 4 4 3 2 2 1 0 0 0 0 0

What I want should look like this;

	0 0 0 0 0 0 4 4 4 4 4 4 4 4 0 0 0 0 0 0
	0 0 0 0 0 0 4 4 4 4 4 4 4 4 0 0 0 0 0 0
	0 0 0 0 0 0 5 5 5 5 5 5 5 5 0 0 0 0 0 0
	0 0 0 0 0 0 4 4 4 4 4 4 4 4 0 0 0 0 0 0
	0 0 0 0 0 0 4 4 4 4 4 4 4 4 0 0 0 0 0 0

Background information;

	- the DGPS data set was from a Trimble unit, with 95% within
	  30cm accuracy,

	- the raster cell size is 5m x 5m,

	- there are often multiple DGPS samples within a cell, because it
	  was a reasonably hot day and I walked slowly with all that
	  equipment on my back,

	- the resultant tracks drawn on a raster need to be enlarged to
	  aid readability, I have not yet chosen the size, though I used
	  eight cells in my example above.

-- 
James Cameron                                      (cameron at stl.dec.com)

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