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On 17/04/2012 10:20, Harald Hofmann wrote:
<blockquote cite="mid:4F8D19A7.6030609@monash.edu" type="cite">Hi,
<br>
sorry, I have a rather simple question.
<br>
<br>
I need to determine the distance in between the points of a vector
layer. I went down a river and had a GPS on a minute scale logging
my position while I was measuring some dissolved gases
continuously in the river water along the flow path.
<br>
I have merged the GPS log with my chemistry data from my data
loggers over the measuring time in R and imported it with
v.in.ascii.
<br>
What I need now is the distance in between the single measuring
points while going downstream for modelling purposes.
<br>
<br>
I spent about an hour trying to find a way to do so and can't
figure it out. Sorry. I bet there must be a simple solution to
that. Using the measuring tool would be cumbersome as I have about
500 points.
<br>
<br>
I looked into v.distance with the GRASS plug-in but that measures
distances between two vector layers, right?
<br>
</blockquote>
<br>
You're on the right track: the v.distance module has a "to_along"
option. Here's what you can do:<br>
<br>
First use the v.in.lines module to import the ascii GPS log points
as a line feature. <br>
v.in.lines gps_points.txt out=river_line fs=, <br>
# (comma separated?) <br>
# This module isn't in the QGIS GRASS toolbox yet, so you'll have to
either run GRASS standalone, or use the GRASS terminal in QGIS<br>
<br>
Now add a column to the points table to accept the distance along
the line:<br>
v.db.addcol gps_points column="along double precision"<br>
<br>
Now run v.distance as:<br>
v.distance from=gps_point to=river_line upload=to_along column=along
out=connectors <br>
# The output parameter hold the line segments connecting each point
to the river_line. It's required by the module to run, by has no
significance for you. <br>
<br>
Cheers,<br>
Micha<br>
<blockquote cite="mid:4F8D19A7.6030609@monash.edu" type="cite">
<br>
Help would be really appreciated. And I am sorry if that has been
asked before but I couldn't find a thread dealing with that.
<br>
<br>
Best regards,
<br>
Harald
<br>
<br>
<br>
</blockquote>
<p><br>
</p>
<br>
<pre class="moz-signature" cols="72">--
Micha Silver
052-3665918
</pre>
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