[Qgis-user] lines with arrowheads

[Andreas Neumann]

Hi Stefanie,

I wonder if your patch just allows the green and red dots at starts and 
ends or if it would allow the placement of arbitrary shapes as markers?

SVG, in my opinion, handles markers nicely, described at 
http://www.w3.org/TR/SVG11/painting.html#Markers

Such an approach would allow a user to specify individual SVG markers to 
be placed at start-points, end-points and any vertices in between.

Visualizing markers in between (marker-mid) is useful in many cases: 
visualization of the vertex positions of reference layers during editing 
a layer. Putting symbols at vertices can be useful in cartography: 
imagine the visualization of powerlines or cablecars where markers could 
be used to symbolize poles.

The SVG model of markers either automatically calculates the orientation 
of the markers (using bisector angles of tangent vectors) or keeps the 
orientation as specified in the marker definition.

I think for a mid-to longterm solution the approach SVG 1.1 full took 
would be useful for QGIS as well, but in the short run Stefanies patch 
would be good enough.

Just my thoughts,
Andreas


Stefanie Tellex wrote:
> I submitted a patch to do this a while back, but I don't think it was 
> accepted.  I thought it was because it was decided to wait until a more 
> modular rendering pipeline was added, but I can't find the messages 
> about that in the thread.   In fact the thread implies it would be 
> accepted, but if it made it into svn, I never noticed it. 
> (http://lists.osgeo.org/pipermail/qgis-developer/2008-February/003248.html)
> 
> The patches are attached.  (arrows_in_linestrings draws arrows; 
> draw_start_and_stop draws a green dot at the start and a red dot at the 
> end.)
> 
> This message suggests an alternative solution that doesn't require 
> compiling qgis yourself:
> http://lists.osgeo.org/pipermail/qgis-developer/2008-February/003250.html
> 
> Stefanie
> 
> 
> 
> 
> 
> M S wrote:
>> One of the outputs from r.flow in GRASS is downslope flow lines.  
>> Without arrowheads (or some similar symbol like that) at the end of 
>> lines pointing which way is downhill, the lines become ambiguous.
>>
>> Is there a way to draw these lines with arrowheads?   Or some other 
>> approach that might achieve this?
>>
>> Mark
>>
>>
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Andreas Neumann
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