[postgis-users] Check and validate directionality of road lines

Gary Turner g at elizr.com
Wed Apr 26 16:46:44 PDT 2023

On your right! ;)

If what you mentioned below is what you actually wanted,  for something 
general you would have to factor in which jurisdiction you are in as to 
which side you drive.

On 26/04/2023 10:18 pm, Shaozhong SHI wrote:
> On Tue, 25 Apr 2023 at 21:18, Richard Greenwood 
> <richard.greenwood at gmail.com> wrote:
>     First you would have to define what valid directionality is.
>     In some cases valid directionality might be that all roads project
>     outward in a cardinal direction from an origin. For example, city
>     blocks running north-south or east-west. In that case you could
>     compare the X or Y coordinates of the start and end points of a
>     linestring to verify that they were larger or smaller as
>     appropriate. e.g. that a north bound road's end point Y was
>     greater than its starting Y. Obviously your data would have to
>     have an attribute that identified if a road was designated
>     north-south or east-west.
>     Another definition of a valid road direction is that it is always
>     radiating out like branches on a tree. This is more common in
>     rural addressing systems. If that's your definition of "valid"
>     then you need to create nodes at the forks, compare these to your
>     linestring starting points and verify that a fork node is not at
>     the end of a linestring.
>     I'm sure there are other definitions of valid directionality,
>     these are just two that I have come across in my work.
>     Rich
>     On Tue, Apr 25, 2023 at 4:10 AM Shaozhong SHI
>     <shishaozhong at gmail.com> wrote:
>         How best to check and validate directionality of road lines?
>         Regards,
>         David
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> It may be a feasible idea to check and validate road lines depicting 
> high ways.  Direction of digitising indicates the direction of road.  
> To test for whether road lines are parallel to each other.  If you 
> travel along one road, you always expect the road line that is on your 
> left should travel in opposite direction.
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