[GRASS-dev] Re: [bug #2765] (grass) v.buffer produces strange results

[Hamish]

> this bug's URL: http://intevation.de/rt/webrt?serial_num=2765

> > Maciek:
> >> square_rot
>  
> > Notice this is not a square of four corners!
> 
> Why the "!", actually?
> 
> > If you zoom in you find it contains 229 vertices, i.e. this is
> > r.to.vect output with steps at the grid resolution. So not as easy
> > to debug by hand
> 
> OK. But this doesn't mean buffering it should be buggy, right?

This is significant as the bug appears on a complex polygon, not a
simple 4 vertex square as it appeared on first look.


> >> ditches
>  
> > I couldn't recreate your buff=1 and 4 errors- buffering works fine
> > for me there.
> 
> I'm wondering why, because I can perfecetly reproduce the bug at any
> time with exactly the data I sent you.
> 
> Are you absolutely sure that the output of following v.buffer
> commands:
> 
>  v.buffer input=ditches output=ditches_buf1 type=area buffer=1
>  v.buffer input=ditches output=ditches_buf4 type=area buffer=4
> 
> looks all OK after you zoom to region 'ditches_buf' included in my
> sample dataset?
> 
> For me it's obvious that the output is plain wrong.

attached is a screenshot of the original vector in "aqua" on top of the
1 and 4 meter buffers I've just created.

looking at "v.info -h" I see that I did load it into v.digit to have a
look at the topology. I've tried again with a fresh copy of the mapset,
same (good) results. I don't know why it would be different- but for me
that works.


But it doesn't matter -- I was looking for a simple example of it going
wrong and I think I've found one:

Can you try buffering this simple polygon and see if it works correctly
for you? (I used a 10m buffer) If we can fix the bug causing that,
maybe your area filling bug will go away too.
 ("v.in.ascii -n format=standard")

B 26
 600039.02641686 5678405.3999173
 600077.97320276 5678399.62882899
 600086.74267773 5678396.53372018
 600165.15210099 5678369.45151806
 600169.2571522 5678367.86458082
 600321.12416744 5678313.92598028
 600329.91897615 5678321.23595115
 600333.66876785 5678318.50222813
 600324.59956919 5678312.02422909
 600321.23100969 5678310.98774925
 600167.57287245 5678364.49602132
 600085.45304905 5678392.66483416
 600077.19942555 5678396.27579444
 600036.44715953 5678401.36982765
 600030.38590477 5678402.27256772
 600010.78354895 5678405.62560227
 599996.21074494 5678408.39830396
 599987.18334424 5678410.71963557
 599979.96142368 5678412.00926424
 599968.01258083 5678413.77867984
 599954.94262744 5678414.84644733
 599949.52618701 5678419.48911054
 599968.61269136 5678418.4574076
 599998.40311369 5678411.75133851
 600001.62800241 5678411.19452149
 600039.02641686 5678405.3999173
C 1 1
 600232.43677669 5678342.9534263
 1 1188



Hamish
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