[GRASS-dev] the function of v.buffer `minordistance' option

[Maciej Sieczka]

W dniu 04.06.2014 21:24, Moritz Lennert pisze:
> On 04/06/14 20:42, Maciej Sieczka wrote:
>> W dniu 04.06.2014 14:53, Moritz Lennert pisze:
>>> On 03/06/14 19:59, Maciej Sieczka wrote:

>>>> Anybody knows what is the v.buffer's `minordistance' option supposed
>>>> to do?
>>>>
>>>> The manual is not verbose about that, but as I understand it, together
>>>> with `distance', it should allow to create a buffer with different
>>>> extent along the minor and major axis, considering the specified
>>>> `angle'
>>>> of their rotation.
>>>>
>>>> But none of the options works as that - the buffer size always equals
>>>> the `distance', and the other 2 options make no difference if used or
>>>> not an set to what.
>>>>
>>>> BTW, it seems that -s, -c flags also don't have any effect on the
>>>> output.
>>>>
>>>> Did I get it wrong or maybe there's something broken?

>>> In NC dataset:
>>>
>>> v.buffer schools_wake out=testbuf distance=500 minordistance=250
>>>
>>> gives me the attached buffers. Everything seems to work fine here...
>>>
>>> Could you be more specific about what exactly is not working for you ?

>> Right, looks fine for points input. Not so for areas input though, e.g:
>>
>> $ v.buffer testbuf out=testbuf2 distance=500 minordistance=250
>>
>> v.buffer in the latter case does not honor minordistance and uses
>> distance for both axes, while I would expect it to behave the way it
>> does for points input. Am I expecting something which is not implemented
>> maybe?

> For me this is more of a conceptual problem: how can you define a major
> and minor axis for buffers of polygons ?

Maybe they cross at the centroid, rotation angle applies?

I was trying to make a minordistance=0.0111111111111111 
distance=0.00694444444444447 vector area buffer in a latlon location. 
The northing/easting difference was supposed to copmpensate for the 
distance distortion, to some extent. But only then it came to me that 
it's better to reproject the input polygon to a metric location, create 
the regular fixed-distance buffer there, and reproject the buffer to the 
latlon location where I need it.

Maciek

-- 
Maciej Sieczka
http://www.sieczka.org


-- 
Maciej Sieczka
http://www.sieczka.org