[postgis-users] Shifting linestrings left

[Ben Madin]

G'day Sean,

On 24/12/2010, at 2:07 AM, Sean wrote:

> Is this just a visualization issue?  You could store copies of the the
> road line with attribute data indicating direction or have a separate
> table with foreign keys to the geography and the direction data.
> 
> Then, you just symbolize differently based on the attributes.  Offset
> the symbology not the geometry.  This is more correct, it preserves
> the information about the actual road on which they travel.  Showing
> direction of travel is strictly a symbology issue.

It's a mix of both - initially, it was a geometry issue - I have linestrings for roads, and for some I have information that suggests that they are dual carriageway, and I was wondering if we could approximate the dual carriageway by shifting the original geometry a little bit to the left going each way.

Then I realised I had better things to do, so I moved on, but now I have a need to show routes going both ways, but using pgRouting they (unsurprisingly) following the same lines, and I wanted to show it. Using QGIS I offset the symbology, but it doesn't actually seem to works how I wanted (which is nicely described by Simon's post), but rather looks like :

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cheers (and Happy Christmas etc)

Ben