[GRASS-user] SOLVED: Re: deleting lines by length, from a vector map

2019-12-01 Thread Zoltan Szecsei 

Hi All,
Thanks go to Markus, Micha and Moritz for contribution.
Having been guided to v.edit, it was quite trivial:

gscript.run_command('v.edit', map=gen, type='line', tool='delete', 
threshold='-1,0,-50', query='length', overwrite=True)


Note the triplet value for Threshold.
Thanks again,
Zoltan

On 2019/11/30 18:43, Markus Neteler wrote:

Hi Zoltan,

On Sat, Nov 30, 2019 at 4:05 PM Zoltan Szecsei  wrote:

Hi,
I'm trying to write my first Grass python script to load Shape files and
delete all lines shorter than 50m
I'm trying various permutations of the command below, but  no success
(No error message and no lines deleted).
Any guidance would be welcome.

gscript.run_command('v.extract','r',input=gen,output=lin,  where="(
$LENGTH > 50 )",overwrite=True)
gscript.run_command('v.out.ogr', 'sce2', input=lin, type='line',
output=dir_rclout + rcl + '.shp', format='ESRI_Shapefile',
output_type='line',overwrite=True)

(writing in a rush, just to send some ideas)

Perhaps something like this:

v.edit:
tool=delete
Delete selected features from vector map
https://grass.osgeo.org/grass78/manuals/v.edit.html

with the related WHERE condition.

The attribute-from-geometry for this WHERE condition you may get with
https://grass.osgeo.org/grass78/manuals/v.univar.html

For the line lengths, perhaps to consider
https://grass.osgeo.org/grass78/manuals/v.build.polylines.html


Thanks and regards,
Zoltan
PS: Should these type of questions go to grass-dev ??

Here is fine as well!

Cheers
Markus


--

=
Zoltan Szecsei GPrGISc 0031
Geograph (Pty) Ltd.
GIS and Photogrammetric Services

P.O. Box 7, Muizenberg 7950, South Africa.

Mobile: +27-83-6004028 (WhatsApp only)
Qatar:  +974 5083 2722 www.geograph.co.za
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--

=
Zoltan Szecsei GPrGISc 0031
Geograph (Pty) Ltd.
GIS and Photogrammetric Services

P.O. Box 7, Muizenberg 7950, South Africa.

Mobile: +27-83-6004028 (WhatsApp only)
Qatar:  +974 5083 2722 www.geograph.co.za
=

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Re: [GRASS-user] deleting lines by length, from a vector map

2019-12-01 Thread Moritz Lennert 

On 1/12/19 08:39, Micha Silver wrote:


On 30/11/2019 16:11, Zoltan Szecsei wrote:

Hi,
I'm trying to write my first Grass python script to load Shape files 
and delete all lines shorter than 50m
I'm trying various permutations of the command below, but  no success 
(No error message and no lines deleted).

Any guidance would be welcome.

gscript.run_command('v.extract','r',input=gen,output=lin, where="( 
$LENGTH > 50 )",overwrite=True)
gscript.run_command('v.out.ogr', 'sce2', input=lin, type='line', 
output=dir_rclout + rcl + '.shp', format='ESRI_Shapefile', 
output_type='line',overwrite=True)




The term $LENGTH looks wrong to me.

In python I usually would do something like:


In [1]: import grass.script as gscript

In [4]: where_expr = "%s > %d" % ("'length'", 5000)

In [5]: where_expr
Out[5]: "'length' > 5000"

In [6]: gscript.run_command('v.extract', input="roads", 
output="roads_long", where=where_expr)


In order for this to work, you need a column 'length' in your attribute 
table. Do you have such a column. Otherwise, you can create it with v.to.db.


Moritz
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