[GRASS-user] serious problem with "ROUND-OFF"

[achim]

Dear users,

I am writing to mention, that I have solved the problem.

For every point (connection between two lines), which is a critical
point (on the border between two raster cells), I did a 'r.what' with a
offset less than half grid-resolution in every direction (ne,nw,se,sw
and n,s and e,w). Because I generated the lines from high raster-values
(river-network), I could choose the cell with the highest value as a
direction for moving node and verts with 'v.edit'.

Thanks for patience, especially Hamish,
Achim

achim schrieb:
> Hi Hamish,
> 
> thanks for your suggestions. It is very useful to get ideas from a
> different perspective!
> 
> I am sorry, that I have to write a 'but' again:
> 
>>> r.to.vect the area
> ..I have no areas to extract. I have a river network, for which I want
> to subdivide some lines.
> Because I have some thousands of lines, I always get some
> start/end-nodes on these critical points on the border between two
> raster-cells.
> 
>>> add cats to boundaries with v.category
>>> v.type the boundary to line
>>> v.extract the lines
>>> v.buffer the lines to about the cell width
>>> v.overlay op=not
> Otherwise that would help!! (Even though v.buffer would take sooo... long)
> 
> Best regards,
> Achim
> 
>>> ?
>>>
>>>
>>> Hamish
>>>
>>>
>>>
>>> --- On Wed, 30/9/09, achim <ak7 at jupiter.uni-freiburg.de> wrote:
>>>
>>>>> From: achim <ak7 at jupiter.uni-freiburg.de>
>>>>> Subject: Re: [GRASS-user] serious problem with "ROUND-OFF"
>>>>> To: "grass-user" <grass-user at lists.osgeo.org>
>>>>> Received: Wednesday, 30 September, 2009, 4:37 AM
>>>>> Dear grass users,
>>>>>
>>>>>
>>>>> I think I know what is needed...
>>>>>
>>>>> to solve the problem (see below, mainly coming from
>>>>> splitting lines on
>>>>> edges between raster-cells), I will have to:
>>>>> 1) identify the verts
>>>>> 2) move these verts on the line (direction of the line) at
>>>>> certain
>>>>> distance (about half grid-size)
>>>>>
>>>>> That would solve the problem mainly, but I have no idea how
>>>>> to deal with it.
>>>>> Any help, suggestions or opinions are very welcome!
>>>>>
>>>>> Thanks in advance,
>>>>> Achim
>>>>>
>>>>> achim schrieb:
>>>>>>> Hi all,
>>>>>>>
>>>>>>> I have a problem, I really would like to solve,
>>>>> because many problems
>>>>>>> occur in my theses in further steps.
>>>>>>>
>>>>>>> What I do is:
>>>>>>>
>>>>>>> 1. I break lines at some lengths.
>>>>>>> 2. I use both vector- and raster-data for analysis,
>>>>> which is eg.
>>>>>>> updating points with raster-values or converting lines
>>>>> and points to raster.
>>>>>>> The Problems are (due to rounding or
>>>>> "non-snapping"?):
>>>>>>> !Points from lines on the edge between two diagonal
>>>>> cells (see pictures)!
>>>>>>> These points do:
>>>>>>> 1. not belong precisely to one cell (compared with the
>>>>> line they come
>>>>>>> from (see picture v.to.rast.png)
>>>>>>> 2. These points sometimes don't lie on on the cells,
>>>>> the line is
>>>>>>> referred to (see picture break.png)
>>>>>>>
>>>>>>> Any hints are very welcomed!
>>>>>>>
>>>>>>> Thanks in advance,
>>>>>>> Achim
>>>>>>>
>>>>>>>
>>>>>>>
> ------------------------------------------------------------------------
>>>>>>>
> ------------------------------------------------------------------------
>>>>>>>
> ------------------------------------------------------------------------
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>>>>>>> grass-user at lists.osgeo.org
>>>>>>> http://lists.osgeo.org/mailman/listinfo/grass-user
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>>>
>>>
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