[GRASS-dev] Re: v.generalize
hmitaso at unity.ncsu.edu
Fri Aug 17 07:05:32 CEST 2007
many thanks for a great new module.
I wanted to write just a few comments but I ended up doing a small
My main interest was to find out how we can use line generalization
to preprocess contours or profiles to avoid some notorius
interpolation problems -
I will write about that in my next message, first some comments:
1. It would be great if you could use the new data set at least for some
examples in the tutorial and manual, Markus has just released version 06
- it is available from here:
It has detailed streams and streets data where the differences
between different methods nicely show up. I haven't tried any areas,
areas, soils and planimetry would be good candidates for generalization.
2. The module indeed needs a tutorial but make sure that you put
detailed description, notes and examples in the man page.
The past experiences show that the man pages are being kept relatively
up-to-date but the tutorials updates tend to be neglected.
3. On technical note - when I tried stream generalization with -r flag
many internal stream segments got removed (the streams essentially
I assume I did not use this option as intended, you may want to explain
the right use in the manual.
4. In relation to your answer to Paul's comments below -
built-in functions for the work with the single points
would be huge help and could eliminate the current mixture of old
and new get-arounds / left-overs from the old site format and troubles
with topology building for larger point data sets. I found the
of points really confusing and not very efficient.
I would like to encourage others to test the module too so that it
can be included into CVS.
I have tried only very little from the rich set of options that the
modules offers so more
testing will help,
Dept. of Marine, Earth and Atm. Sciences
1125 Jordan Hall, NCSU Box 8208,
Raleigh NC 27695
On Aug 4, 2007, at 4:57 PM, Daniel Bundala wrote:
> Hello Paul, Wolf and List
> On 8/4/07, Paul Kelly <paul-grass at stjohnspoint.co.uk> wrote:
>> On Thu, 26 Jul 2007, Wolf Bergenheim wrote:
>>> v.generalize is fully functional complete with manual and
>>> smoothing and
>>> simplification operations. The module works with both areas and
>>> Attribute tables are also copied and cats are preserved. Please
>>> give the
>>> module a try and send us feedback!
>>> The rest of SoC will be spent in implementing other generalization
>>> operations and getting all the rest of the bugs out.
>> Hello Wolf and Daniel
>> Now I've had time to look at v.generalize too and am very
>> impressed. The
>> amount of easily-accessible functionality that this module adds to
>> GRASS vector capabilities really seems to be something
>> significant. At
>> first glance the amount of options seemed overwhelming but on reading
>> through the man page and looking at the references there it became
>> more obvious. I think it could still be made clearer, but there is
>> a lot of information and explanation there and also in the source
>> which is good.
> This is true. Actually, the man page does not contain any examples. I
> will try to improve this... Moreover, I am planning to write a
> tutorial/GSoC Final Report which will demonstrate the capabilities of
> this module with a lot of examples and nice pictures...
>> The main thing I was wondering about is whether the threshold
>> parameter is
>> dual-purpose? If I understand correctly, is it used in some
>> algorithms but
>> then again also at the end to remove lines left that are shorter
>> and areas
>> that are smaller than the threshold? Is that dual purpose use
>> likely to
>> cause any problems? Or should these be different parameters?
> Yes, you understand it correctly. But this happens only if you
> simplify the lines. Just few days ago, I added new flag (-r) to the
> module which specifies whether the small/short linear features are
> romeved. It is also mentioned somewhere in the newest version of the
> man page.
>> I am curious too as to the spelling of alfa rather than alpha!
> Oops. I think that this caused me some problems with TeX as well.... I
> will change it.
>> Compiling with -Wall I see quite a lot of missing function
>> prototypes - as
>> for the other Summer of Code module I feel putting in a
>> local_proto.h for
>> the functions that can be called from other source files, and marking
>> the functions local to each file as static, would make things a bit
>> clearer. Also perhaps Doxygen-style documentation for the
>> functions? This
>> one's not a big deal at all. I know it's a bit of work but the
>> look well organised already, so presumably there is a lot of thought
>> behind the way they are and it should be easy enough to put that into
>> words. But in general the code comments are really good and
>> helpful - only
>> there where they are needed and left out where it is obvious by
>> the code, what is going on.
> Glad you like me style of comments... You know, *the* most boring part
> of the project. And I will check that -Wall stuff.
>> Was thinking too about all the matrix stuff in the matrix.c file -
>> for this lazy question, as if I had more time to look through and
>> was more
>> familiar with these things I could answer it myself - but is it
>> than the G_matrix_* functions in lib/gmath, or just an alternative?
> It is probably just an alternative, but it was meant to better:) In
> the beginnings, it seemed that I will be working with the special type
> of sparse matrices only. But this is no more the case.
>> Would also be interesting to hear if Daniel has any suggestions for
>> improvements and tidying of the vector API in GRASS. I enjoyed
>> reading the
>> code and it seems to utilise the existing API very well, which
>> makes me
>> think it's possible suggestions for enhancements and further
>> of the API could even come out of this work.
> Hmmm, maybe, I was really missing built-in functions for the work with
> the single points/vectors. (Vector from
> mathematical/geometrical/physical point of view) Something I have
> implemented in point.*
>> But in summary, I had to search hard to find these few suggestions
>> improvement! It looks like a really excellent piece of work and it
>> will be
>> great to have it in GRASS.
> Thanks Paul for your feedback!
> I dont know what commit/version did you use, but from the above, it
> seems that it was not the very last commit. Well, there were no
> changes in the code, but I documented displacement and "network
> generalization" operations. Just to keep you informed about the newest
> functionalities of v.generalize:) To tell the truth, "displacement"
> has very impressive results! (Stay tuned for the tutorial, everything
> will be there:)
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