[GRASS-user] multiple

[Frank David]

Hi Stephan,

Thanks for your message. I got intersection point with your method. I 
did not succeed to add cat to the error v.clean with v.category 
(database connection is missing ?). Anyway, another problem is I cannot 
copy attribute table v.patch. So I have to do a v.what on my original 
river lines to get its name and v.to.db to get coordinates. It's quite a 
long process, and my data counts numerous lines (river our roads, 
between 500 upto 2000 lines)... I will try

Another way could be to use v.buffer for transect lines and use this 
buffer as transect with v.overlay. I keep the attribute table and I can 
get coordinate with v.to.db. Do you think it is suitable ?

I think v.profile should be the way, but this function is not available yet.

Regards,

Frank


Le 27/04/2022 à 23:02, Stefan Blumentrath a écrit :
>
> Hi Frank,
>
> Yes, you are right. To get the intersection point you patch the line 
> maps (v.patch), use v.clean on the patched maps and sve the 
> intersection points (errors option in v.clean). Then you add 
> categories to the generated points with v.category…
>
> That just for correction of my earlier suggestion. Your approach with 
> v.profile seems way more appropriate.
>
> If all your lines have the same cat value, you could create new, 
> induvial cat values with v.category, before you run v.profile (I have 
> not looked at your dataset yet…)?
>
> Cheers
>
> Stefan
>
> *From:*Frank David <frank.david at geophom.fr>
> *Sent:* onsdag 27. april 2022 19:23
> *To:* Stefan Blumentrath <Stefan.Blumentrath at nina.no>; GRASS user list 
> <grass-user at lists.osgeo.org>
> *Subject:* Re: [GRASS-user] multiple
>
> Hi Stephan,
>
> I'm not very used to v.overlay, but it seems to be used with area and 
> not with lines crossing lines, isn't it ?
>
> Frank
>
> Le 27/04/2022 à 09:14, Stefan Blumentrath a écrit :
>
>     Hi Frank,
>
>     My general approach would be like this:
>
>     v.overay to intersect transects and lines
>
>     v.to.points use=start to get transect start points
>
>     v.distance to get distance from transect start point to point where lines cross
>
>     With v.distance you need to try whether it is sufficient to compute distance to the nearest point only or if you need to compute distance to all intersection points within the distance equal to the length of the transect...
>
>     If the latter is the case you would need to filter out lines with distances that are not along a transect.
>
>     Hope that helps.
>
>     v.distance can produce lines, so you could check visually if the approach works as expected.
>
>     Just a suggestion.
>
>     Cheers
>
>     Stefan
>
>     -----Original Message-----
>
>     From: grass-user<grass-user-bounces at lists.osgeo.org>  <mailto:grass-user-bounces at lists.osgeo.org>  On Behalf Of Frank David
>
>     Sent: tirsdag 26. april 2022 20:01
>
>     To: GRASS user list<grass-user at lists.osgeo.org>  <mailto:grass-user at lists.osgeo.org>
>
>     Subject: [GRASS-user] multiple
>
>     Hello,
>
>     I need to identify vector lines (like roads, rivers) crossed by a transect and get distance from the beginning of the transect. For the moment I'm using v.profile but it returns only the first item. Is there any way to get all crossed lines ?
>
>     Thank for your help,
>
>     Frank
>
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