Hello,
I have a vector line file that has lots of two-vertex lines. Many of
these two-vertex lines share endpoints and really just make parts of one
longer line. I'd like to dissolve these lines into one line when they
have the same end point. It looks like v.dissolve only works for areas.
Is there somewhere else I should be looking? Thank you.
Bryan
On 10/19/2010 11:17 PM, Bryan Keith wrote:
Hello,
I have a vector line file that has lots of two-vertex lines. Many of
these two-vertex lines share endpoints and really just make parts of one
longer line. I'd like to dissolve these lines into one line when they
have the same end point. It looks like v.dissolve only works for areas.
Is there somewhere else I should be looking? Thank you.
Did you have a look at v.build.polylines ?
Additional note: line vectors have a direction. Two line segments with an equivalent node (end point) will *not* connect if they are in opposite directions. In this case you can try the v.edit tool=flip option (on those segments only)
Bryan
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Micha Silver
Arava Development Co. +972-52-3665918
http://www.surfaces.co.il
Micha Silver wrote:
Bryan Keith wrote:
Hello,
I have a vector line file that has lots of two-vertex lines. Many of
these two-vertex lines share endpoints and really just make parts of one
longer line. I'd like to dissolve these lines into one line when they
have the same end point. It looks like v.dissolve only works for areas.
Is there somewhere else I should be looking? Thank you.Did you have a look at v.build.polylines ?
Additional note: line vectors have a direction. Two line segments with an
equivalent node (end point) will *not* connect if they are in opposite
directions.
Each line has two nodes, one at the start and one at the end. If at
the end of one line any other line is starting or ending, this other
line is added to the first line, reversing the direction if necessary.
IOW, two lines with a common node will indeed connect, and the
direction of one line may need to be reversed (done automatically).
Very simple to test by digitizing a simple test vector.
In this case you can try the v.edit tool=flip option (on those
segments only)
Should not be needed as pre-processing step for v.build.polylines.
Markus M
On 20/10/2010 08:36, Markus Metz wrote:
Micha Silver wrote:
Bryan Keith wrote:
Hello,
I have a vector line file that has lots of two-vertex lines. Many of
these two-vertex lines share endpoints and really just make parts of one
longer line. I'd like to dissolve these lines into one line when they
have the same end point. It looks like v.dissolve only works for areas.
Is there somewhere else I should be looking? Thank you.Did you have a look at v.build.polylines ?
Additional note: line vectors have a direction. Two line segments with an
equivalent node (end point) will *not* connect if they are in opposite
directions.Each line has two nodes, one at the start and one at the end. If at
the end of one line any other line is starting or ending, this other
line is added to the first line, reversing the direction if necessary.
IOW, two lines with a common node will indeed connect, and the
direction of one line may need to be reversed (done automatically).
Very simple to test by digitizing a simple test vector.
Heh, thanks for the correction!
Was this always the case? I seem to remember not be able to merge lines unless they were connected in the same direction.
How does the line reversal work? That is, Which of the two line segments is chosen be get reversed?
Regards,
Micha
In this case you can try the v.edit tool=flip option (on those
segments only)
Should not be needed as pre-processing step for v.build.polylines.
Markus M
This mail was received via Mail-SeCure System.
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Micha Silver
http://www.surfaces.co.il/
Arava Development Co. +972-52-3665918
If You have lines with wrong direction or segment order, You can try
to run my "v.reorder_line_segments" tool.[1] It will try to reorder
same CAT line segments to be in increasing order. It also reverses
line segments to be in order from start to end. It will work only for
simple, stright lines and will go nuts on circular featrues etc, still
sometimes it's faster than doing manual work.
Current version will stop if line contains crossection, still that
check can be removed. I introduced it only because module entered an
endless loop if multiline looped back to itself. Code is unfinished,
as I was not able to figure out how to solve non-trivial cases and
thus cleaned my data by hand.
It's tested on GRASS 7. It requires ctypes.
If You need aditional help, drop a note.
Maris.
1. http://www.gisnet.lv/trac/gisnet/browser/gisnettools/v.reorder_line_segments.py
2010/10/20, Micha Silver <micha@arava.co.il>:
On 20/10/2010 08:36, Markus Metz wrote:
Micha Silver wrote:
Bryan Keith wrote:
Hello,
I have a vector line file that has lots of two-vertex lines. Many of
these two-vertex lines share endpoints and really just make parts of one
longer line. I'd like to dissolve these lines into one line when they
have the same end point. It looks like v.dissolve only works for areas.
Is there somewhere else I should be looking? Thank you.Did you have a look at v.build.polylines ?
Additional note: line vectors have a direction. Two line segments with an
equivalent node (end point) will *not* connect if they are in opposite
directions.Each line has two nodes, one at the start and one at the end. If at
the end of one line any other line is starting or ending, this other
line is added to the first line, reversing the direction if necessary.
IOW, two lines with a common node will indeed connect, and the
direction of one line may need to be reversed (done automatically).
Very simple to test by digitizing a simple test vector.Heh, thanks for the correction!
Was this always the case? I seem to remember not be able to
merge lines unless they were connected in the same direction.
How does the line reversal work? That is, Which of the two
line segments is chosen be get reversed?
Regards,
MichaIn this case you can try the v.edit tool=flip option (on those
segments only)
Should not be needed as pre-processing step for v.build.polylines.
Markus M
This mail was received via Mail-SeCure System.
--
Micha Silver
http://www.surfaces.co.il/
Arava Development Co. +972-52-3665918_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user
Micha Silver wrote:
On 20/10/2010 08:36, Markus Metz wrote:
Micha Silver wrote:
Bryan Keith wrote:
Hello,
I have a vector line file that has lots of two-vertex lines. Many of
these two-vertex lines share endpoints and really just make parts of one
longer line. I'd like to dissolve these lines into one line when they
have the same end point. It looks like v.dissolve only works for areas.
Is there somewhere else I should be looking? Thank you.Did you have a look at v.build.polylines ?
Additional note: line vectors have a direction. Two line segments with an
equivalent node (end point) will *not* connect if they are in opposite
directions.Each line has two nodes, one at the start and one at the end. If at
the end of one line any other line is starting or ending, this other
line is added to the first line, reversing the direction if necessary.
IOW, two lines with a common node will indeed connect, and the
direction of one line may need to be reversed (done automatically).
Very simple to test by digitizing a simple test vector.Heh, thanks for the correction!
Was this always the case? I seem to remember not be able to merge lines
unless they were connected in the same direction.
How does the line reversal work? That is, Which of the two line segments is
chosen be get reversed?
v.build.polyline works as follows:
it picks a line and from its start node, walks back as long as exactly
one other line is connected to this node. Line directions are reversed
as required, i.e. it does not matter if the next line is connected to
the current node by its start or end node.
Once the start line of a polyline is identified, it walks forward and
adds all vertices (in reverse order if needed) of connected lines to
the start line, i.e. the start line and connecting lines are reversed
as needed. That is, if a line is reversed depends on what node is
initially picked for building polylines.
If the direction of lines is important (it's not for boundaries to
build areas), you have to manually change line directions with either
v.edit or the wxdigitizer or the tool by Maris.
Markus M
Regards,
MichaIn this case you can try the v.edit tool=flip option (on those
segments only)
Should not be needed as pre-processing step for v.build.polylines.
Markus M
This mail was received via Mail-SeCure System.
--
Micha Silver
http://www.surfaces.co.il/
Arava Development Co. +972-52-3665918
Hi,
2010/10/20 Markus Metz <markus.metz.giswork@googlemail.com>:
v.build.polyline works as follows:
it picks a line and from its start node, walks back as long as exactly
one other line is connected to this node. Line directions are reversed
as required, i.e. it does not matter if the next line is connected to
the current node by its start or end node.Once the start line of a polyline is identified, it walks forward and
adds all vertices (in reverse order if needed) of connected lines to
the start line, i.e. the start line and connecting lines are reversed
as needed. That is, if a line is reversed depends on what node is
initially picked for building polylines.If the direction of lines is important (it's not for boundaries to
build areas), you have to manually change line directions with either
v.edit or the wxdigitizer or the tool by Maris.
I took a liberty to add your useful notes to v.build.polylines manual - r43979.
Martin
--
Martin Landa <landa.martin gmail.com> * http://geo.fsv.cvut.cz/~landa
On 10/19/2010 11:17 PM, Bryan Keith wrote:
Hello,
I have a vector line file that has lots of two-vertex lines. Many of
these two-vertex lines share endpoints and really just make parts of one
longer line. I'd like to dissolve these lines into one line when they
have the same end point. It looks like v.dissolve only works for areas.
Is there somewhere else I should be looking? Thank you.Did you have a look at v.build.polylines ?
Additional note: line vectors have a direction. Two line segments with
an equivalent node (end point) will *not* connect if they are in
opposite directions. In this case you can try the v.edit tool=flip
option (on those segments only)
Thank you for the response. I finally got around to looking at this
today. I made a simple example and tested with v.build.polylines, and it
works great. Thank you.
However, it turns out that I have many duplicate lines in my dataset. I
created a simple example where there are duplicate lines, and
v.build.polylines doesn't work in that case. What do I need to look at to
get rid of duplicate lines?
Bryan
_____________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-userThis mail was received via Mail-SeCure System.
--
Micha Silver
Arava Development Co. +972-52-3665918
http://www.surfaces.co.il
On 11/05/2010 09:59 PM, Bryan Keith wrote:
On 10/19/2010 11:17 PM, Bryan Keith wrote:
Hello,
I have a vector line file that has lots of two-vertex lines. Many of
these two-vertex lines share endpoints and really just make parts of one
longer line. I'd like to dissolve these lines into one line when they
have the same end point. It looks like v.dissolve only works for areas.
Is there somewhere else I should be looking? Thank you.Did you have a look at v.build.polylines ?
Additional note: line vectors have a direction. Two line segments with
an equivalent node (end point) will *not* connect if they are in
opposite directions. In this case you can try the v.edit tool=flip
option (on those segments only)
Thank you for the response. I finally got around to looking at this
today. I made a simple example and tested with v.build.polylines, and it
works great. Thank you.However, it turns out that I have many duplicate lines in my dataset. I
created a simple example where there are duplicate lines, and
v.build.polylines doesn't work in that case. What do I need to look at to
get rid of duplicate lines?
v.clean tool=rmdupl
Might do it if the lines exactly overlap.
Bryan
On 11/05/2010 09:59 PM, Bryan Keith wrote:
On 10/19/2010 11:17 PM, Bryan Keith wrote:
Hello,
I have a vector line file that has lots of two-vertex lines. Many of
these two-vertex lines share endpoints and really just make parts of
one
longer line. I'd like to dissolve these lines into one line when they
have the same end point. It looks like v.dissolve only works for
areas.
Is there somewhere else I should be looking? Thank you.Did you have a look at v.build.polylines ?
Additional note: line vectors have a direction. Two line segments with
an equivalent node (end point) will *not* connect if they are in
opposite directions. In this case you can try the v.edit tool=flip
option (on those segments only)Thank you for the response. I finally got around to looking at this
today. I made a simple example and tested with v.build.polylines, and
it
works great. Thank you.However, it turns out that I have many duplicate lines in my dataset. I
created a simple example where there are duplicate lines, and
v.build.polylines doesn't work in that case. What do I need to look at
to
get rid of duplicate lines?v.clean tool=rmdupl
Might do it if the lines exactly overlap.
Yes, that worked in my case. Thanks so much, Micha!
Bryan