[GRASS-user] Working with transects

[Maris Nartiss]

Hello GRASSers!

I have transect data as points and I need to identify slope
break-points along transect. If anyone has worked with similar
problem, can offer some solution or give a peace of advice - I would
be thankfull.

More detailed description.
I have height measurements made in form of transects (see attached
sample). Those transects are almost straight and almost perpendicular
to ancient shorelines (strandlines). My task is simple - I have to
create profiles in order to locate ancient shoreline exact position
(they should show up as specific break points on profile).
Currently I have imported data as vector points (v.in.ogr), created
convex hull (v.hull), created buffer around convex hull (v.buffer),
converted result to raster mask (v.to.rast) and then interpolated
surface from loaded points with various methods (v.surf.rst,
v.surf.idw, v.surf.bspline).
Interpolation results differ significantly (see attached sample of
same profile line values on different interpolated surfaces). I know,
that I can tweak v.surf.rst parameters to get better(?) results, still
I have not yet worked with such spatial distribution data and thus
have no idea how to do that.
List of current problems/shortcomings:
* how to extract vector point values along profile line or get vector
point attribute data for nearest points to profile line (vector line
in general)? v.profile/v.transect?
* which of the GRASS offered data interpolation methods is the best to
interpolate data on transect?
* any other tools, that could suit better for this task?

Thanks for reading this and sorry for my clumsy language,
Maris.
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