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

GRASS GRASS user
1

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@jupiter.uni-freiburg.de> wrote:
>

>> From: achim <ak7@jupiter.uni-freiburg.de>
>> Subject: Re: [GRASS-user] serious problem with "ROUND-OFF"
>> To: "grass-user" <grass-user@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@lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/grass-user

>> -----Inline Attachment Follows-----
>>
>> _______________________________________________
>> grass-user mailing list
>> grass-user@lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/grass-user
>>

>
>
>

2

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@jupiter.uni-freiburg.de> wrote:

From: achim <ak7@jupiter.uni-freiburg.de>
Subject: Re: [GRASS-user] serious problem with "ROUND-OFF"
To: "grass-user" <grass-user@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

------------------------------------------------------------------------

------------------------------------------------------------------------

------------------------------------------------------------------------

_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

-----Inline Attachment Follows-----

_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

3

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@jupiter.uni-freiburg.de> wrote:

From: achim <ak7@jupiter.uni-freiburg.de>
Subject: Re: [GRASS-user] serious problem with "ROUND-OFF"
To: "grass-user" <grass-user@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

------------------------------------------------------------------------

------------------------------------------------------------------------

------------------------------------------------------------------------

_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

-----Inline Attachment Follows-----

_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

4

achim wrote:

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:

Hamish:

> > 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

sorry I was thinking of a screenshot posted in the last days
to remove a boundary which touched the side of a polygon with
that.

glad you fixed it with r.what.

Hamish