[GRASS-dev] [GRASS GIS] #2669: v.net.iso: different results depending on direction

[GRASS GIS]

#2669: v.net.iso: different results depending on direction
--------------------------+----------------------------------------------
  Reporter:  mlennert     |      Owner:  grass-dev@…
      Type:  defect       |     Status:  new
  Priority:  normal       |  Milestone:  7.0.1
 Component:  Vector       |    Version:  svn-trunk
Resolution:               |   Keywords:  network v.net.iso direction cost
       CPU:  Unspecified  |   Platform:  Unspecified
--------------------------+----------------------------------------------

Comment (by mlennert):

 Apparently the problem arises when lines are diagonal (in comparison to NS
 or EW direction). Here's a reproducible testcase:

 * horizontal

 {{{
 v.in.lines in=- out=testline sep=, --o << EOF
 610000,225000
 680000,225000
 EOF
 echo "645000|225000" | v.in.ascii in=- out=testpoint --o
 v.net testline point=testpoint op=connect thresh=500 out=testnet --o
 v.db.addtable testnet col="length double precision, cost double precision"
 v.to.db testnet op=length col=length
 v.db.update testnet col=cost qcol="length/(100*1000/60)"
 v.net.iso testnet out=testiso center_cats=1-999 costs=10,20,30,40
 arc_column=cost --o
 }}}

 * diagonal


 {{{
 v.in.lines in=- out=testline sep=, --o << EOF
 610000,200000
 680000,300000
 EOF
 echo "645000|225000" | v.in.ascii in=- out=testpoint --o
 v.net -s testline point=testpoint op=connect thresh=50000 out=testnet --o
 v.db.addtable testnet col="length double precision, cost double precision"
 v.to.db testnet op=length col=length
 v.db.update testnet col=cost qcol="length/(100*1000/60)"
 v.net.iso testnet out=testiso center_cats=1-999 costs=10,20,30,40,50,60,70
 arc_column=cost --o
 }}}

 * vectical


 {{{
 v.in.lines in=- out=testline sep=, --o << EOF
 645000,200000
 645000,300000
 EOF
 echo "645000|250000" | v.in.ascii in=- out=testpoint --o
 v.net -s testline point=testpoint op=connect thresh=50000 out=testnet --o
 v.db.addtable testnet col="length double precision, cost double precision"
 v.to.db testnet op=length col=length
 v.db.update testnet col=cost qcol="length/(100*1000/60)"
 v.net.iso testnet out=testiso center_cats=1-999 costs=10,20,30,40,50,60,70
 arc_column=cost --o
 }}}

 I'll attach the respective images. In the diagonal case, the isochrones
 are much closer towards the South-West (~37km - using the wxgui measuring
 tool - to reach the beginning of cat=8) than towards the North-East (~78km
 to reach the beginning of cat=8). As cost is defined via only one column,
 it should be identical in both directions.

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2669#comment:1>
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