[GRASS-dev] [grass-code I][342] v.clean tool=snap: doubled vertices in the output

[grass-codei at wald.intevation.org]

code I item #342, was opened at 2007-03-25 13:48
Status: Open
Priority: 3
Submitted By: Maciej Sieczka (msieczka)
Assigned to: Nobody (None)
Summary: v.clean tool=snap: doubled vertices in the output 
Issue type: module bug
Issue status: None
GRASS version: CVS HEAD
GRASS component: vector
Operating system: all
Operating system version: 
GRASS CVS checkout date, if applies (YYMMDD): 070325


Initial Comment:
As the title reads. To reproduce, do the following:

1. Import an example line:

$ echo "L  17 1
 592300.58091286 4921395.5186722
 592717.09543568 4921990.53941909
 593252.61410788 4920889.75103734
 594026.14107884 4921812.03319502
 594323.65145228 4920889.75103734
 594888.92116183 4921752.53112033
 595305.43568465 4920889.75103734
 595989.70954357 4921484.77178423
 596376.47302905 4920830.24896266
 596971.49377593 4921514.52282158
 597566.51452282 4920740.99585062
 598102.03319502 4921306.26556017
 598637.55186722 4920592.2406639
 599351.57676349 4921187.26141079
 599797.84232365 4920562.48962656
 600273.85892116 4920979.00414938
 600690.37344398 4920651.74273859
 1     1" | v.in.ascii -n out=zigzag format=standard 

2. Snap each second vertex:

$ v.clean input=zigzag output=zigzag_snap type=line tool=snap thresh=1200

3. See the doubled vertices:

$ v.out.ascii zigzag_snap format=standard | awk 'NR>10'
L  17 1
 592300.58091286 4921395.5186722
 592300.58091286 4921395.5186722
 592300.58091286 4921395.5186722
 594026.14107884 4921812.03319502
 595305.43568465 4920889.75103734
 595305.43568465 4920889.75103734
 595305.43568465 4920889.75103734
 596971.49377593 4921514.52282158
 596971.49377593 4921514.52282158
 596971.49377593 4921514.52282158
 598637.55186722 4920592.2406639
 598637.55186722 4920592.2406639
 598637.55186722 4920592.2406639
 600273.85892116 4920979.00414938
 600273.85892116 4920979.00414938
 600273.85892116 4920979.00414938
 600273.85892116 4920979.00414938
 1     1



There was a similar bug in v.build.polylines [1], fixed in 6.3 CVS by Martin Landa [2] recently.

Workaurond (same as for RT #4249 v.build.polylines bug): run 'v.clean tool=prune thresh=0' on the v.clean tool=snap output. It will remove the bogus doubled vertices.

Maciek

[1]https://intevation.de/rt/webrt?serial_num=4249
[2]http://grass.itc.it/pipermail/grass-commit/2007-February/027003.html


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