[postgis-users] Fwd: line direction

[franco base]

Hi Stephen
How can you explain that the st_offsetcurve make offset according to line
direction.

For example
SELECT ST_OffsetCurve (geom, -20)  as geom_off
FROM table
WHERE id_arc in (1690,1693)

give me the result that you can see in the attached image rendering in qgis
(One Direction on the left, the other on the right).

So I have the dirction information inside the arc geometry.



Thanks
fb


2013/5/16 Stephen Woodbridge <woodbri at swoodbridge.com>

> How do you define arc direction?
> If you had a function:
>
> select getArcDirection(arc);
>
> What would you expect the output to be?
>
> In your image, the arc direction is a function of the labeling algorithm
> in combination with this that of the arc. For example if the label were
> flipped upside down and written along the underside of the line then the
> arc direction symbol would have to be reversed. So we can see that it is a
> function of the label and not just the arc alone.
>
> postgis does not do rendering so it can not define that.
>
> -Steve
>
>
> On 5/16/2013 11:14 AM, franco base wrote:
>
>> I send again message because it was blocked for the attcahed file too big
>>
>>
>> I have a public transport network with an arc for 2 Point(the bus stop).
>> I'd know without using the points information arc direction like in qgis
>> (as you can see from the attached imagine with arc_id and direction)
>>
>>
>> 2013/5/14 Nicolas Ribot <nicolas.ribot at gmail.com
>> <mailto:nicolas.ribot at gmail.**com <nicolas.ribot at gmail.com>>>
>>
>>
>>     Hi,
>>
>>     If you want to materialize direction from start to end of line, you
>>     can use st_startPoint and st_endpoint to determines the right ends.
>>     What is your use case ?
>>
>>     Nicolas
>>
>>
>>     On 14 May 2013 13:49, franco base <frenk.calza at gmail.com
>>     <mailto:frenk.calza at gmail.com>**> wrote:
>>
>>         Hi.
>>         I know tgis function but doesn't work.
>>         Myabe my question isn't correct.
>>         I'd have a binary value according to the arc direction.
>>         For example, in qgis I can view this information:
>>         I can see an arrow on my arc according to direction.
>>         I'd have the same using postgis.
>>
>>         Thanks
>>
>>
>>
>>         2013/5/14 Paolo Corti <pcorti at gmail.com <mailto:pcorti at gmail.com
>> >>
>>
>>
>>             On Tue, May 14, 2013 at 6:03 PM, franco base
>>             <frenk.calza at gmail.com <mailto:frenk.calza at gmail.com>**>
>> wrote:
>>              > Hi.
>>              > I have a question for the list.
>>              >
>>              > Is there a postgis function to have line direction?
>>              >
>>
>>             http://postgis.refractions.**net/docs/ST_Azimuth.html<http://postgis.refractions.net/docs/ST_Azimuth.html>
>>
>>             regards
>>             p
>>
>>             --
>>             Paolo Corti
>>             Geospatial software developer
>>             web: http://www.paolocorti.net
>>             twitter: @capooti
>>             skype: capooti
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