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

[Maciej Sieczka]

Hamish wrote:
> Maciej Sieczka wrote:
>> Wow, this looks OK indeed. Look at my buf_bugs.png screenshot of the
>> same area - red is  4m buffer, green is 1m buffer. Both are all wrong.
>> I wonder how such a difference between your and my results is
>> possible.
> 
> Unless "ditches" is slightly different, I don't know.

My "ditches" is *identical* to what I sent you. Very strange.

> The 4m buffer blob
> seems to me to be the same disease as the lump in "my" area.
> 
> maybe try v.build.polyline?

v.build.polylines is buggy, especially for closed lines like area
boundaries:

http://intevation.de/rt/webrt?serial_num=4249
http://intevation.de/rt/webrt?serial_num=4247

and I avoid using it - not to screw my data.

>>> 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.
>> I tried. You can see the result of buffering at 10m on the attached
>> screendumps:
>>
>> hamish_area.png 	- your input area
>> hamish_area_buf10.png	- 10m buffer
>> hamish_area_both.png	- both, overlayed
>>
>> The 10m buffer is wrong. I'm curious if you obtain *the same* wrong
>> buffer.
> 
> I get identical results, which is reassuring. (this is cat #1188 or so
> from the 'ditches' map)

Some good news! Do you maybe have an idea how to fix that?

Maciek