[mapserver-users] Rendering Challenges

[thomas bonfort]

Brent,

those are interesting questions

On Mon, May 9, 2011 at 21:51, Brent Fraser <bfraser at geoanalytic.com> wrote:
>  While testing v6, I can up with the following list of things I couldn't do
> (see http://i56.tinypic.com/8vvprn.png for a graphic):
>
> 1. Render lines inside polygon boundary (with or without opacity)
Along with Steve's buffer proposition, you can already more or less do
that with OFFSET , except you don't have the notion of inside/outside,
but left/right. If all your polygons are digitized in the same
direction (i.e. clockwise or anticlockwise) this can be done with:

STYLE
  #FILL
END
STYLE
   OUTLINECOLOR r g b
   OFFSET 1.5 -99
   WIDTH 3
   OPACITY 50
END



> 2. Place polygon annotation on/inside boundary line
> (http://trac.osgeo.org/mapserver/ticket/1592 point 8.)
not possible in a single step, but by using the polygon layer a second
time in a TYPE LINE layer for labelling should get you close.

> 3. Rotate anno if required to fit inside a polygon
would be a nice addition, ANGLE AUTO for polygon labels. We should
probably give some way to define if the label should always follow the
longest polygon diagonal, or if it should be first placed horizontally
and fall back to automatic angling only if the horizontal one does not
fit.

> 4. Place polygon annotation outside polygon if anno doesn't fit inside
The fine tuning on how to place the label text compared to the feature
would require new mapfile keywords, but that would seem possible to
implement. I'm not sure these kind of automatic adjustments would
really enhance the rendered quality though.

> 5. Place line anno above (or below) when using ANGLE FOLLOW
This is something I would like to add to. There's a paper detailing
the underlying algorithm here:
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.24.6970

> 6. Rotate vector symbols to follow lines (a font might work but is a pain to
> create)
how is this different than what we already have with a negative GAP?
On a side note, vector symbols are currently rather ill-defined in
mapserver and would need to be tightened up before being able to use
them for precise symbol placement like here.

> 7. User specified character spacing
SIZE AUTO for labels in polygon layers would be a nice addition. We'd
have to be able to define how the size of the font varies in
accordance with the spacing that is applied between characters.
Before going down that road, we shall have to implement the
refactoring proposed in http://trac.osgeo.org/mapserver/ticket/3611 so
as not to clutter the glyph rendering functions of each renderer.


> 8. Erase lines (but not other objects) under annotation
This seems rather involved. It would be difficult to keep the ordering
of layers, as the modified feature could only be drawn during the
labelcache phase, i.e. after all other features in the map.

>
>  My goal was to use the published shp files
> (http://ftp2.cits.rncan.gc.ca/pub/canvec/50k_shp/092/h/canvec_092h06_shp.zip)
> without modification and see how close I could get to the published PDF
> (http://ftp2.cits.rncan.gc.ca/pub/cantopo/50k_geopdf/092/h/cantopo_092h06_geopdf.zip).
>
>  Any suggested rendering techniques are appreciated.  I'll file tickets for
> those problems deemed worthy.

So, most of these enhancements seem possible, some were already on my
laundry-list of rendering enhancements I'd like to tackle. Creating
enhancement tickets for those features is a first step, and funding
them is the second ;)

regards,

thomas

>
> --
> Best Regards,
> Brent Fraser
>
>
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