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

[achim]

Hi,

I can find out critical points between raster-cells,
I can move the verts,
but I cannot decide in which direction:

I tried with:
lon=0.0666666666666674+0.0001
lat=15.2333333333333+0.0001
v.what -a map=linesmap east_north=$lon,$lat distance=0.0000001

to find out, if there, next to the point, is a line (same distance east
and north), if not the line must be in east-south direction.

But v.what only returns informations about points ??<- I guess

Do anybody know, how to find out, in what direction a line-segment is
orientated? (I have a point, connected with two polylines. So one
segment of the one is oriented in one direction, the other in the
opposite direction.)

Thanks,
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 mailing list
>>>>>>> grass-user at lists.osgeo.org
>>>>>>> http://lists.osgeo.org/mailman/listinfo/grass-user
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>>>
>>>
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