On Tue, Jun 30, 2015 at 11:21 PM, Gabriel Roldan <groldan@anonymised.com>
wrote:
Thought it did exist but it looks like it doesn't, so it might make for a
nice weekend project.
I know what the gt-grid module does but never used it. Yet it'd be quite
handy to be able of configuring a read only grid layer in geoserver that
doesn't take any space on disk but is computed on the fly using gt-grid?
quite the same that's done by the mini-wms embedded in the geoserver SRS
List demo, but for general use (see where the map showing the area of
validity for each CRS has a grid on it? [1]).
But before giving it a shot:
- really it doesn't exist?
- would it be useful for others at all?
- if so, feature requests?
Hi Gabriel,
there is much to say on the topic, in summary, it's not as easy as it looks
(doing the store it's indeed easy, using it for grids not as easy as it
seems).
First, Ian has been looking into the subject recently, you might want to
synch up with him:
http://blog.ianturton.com/geotools/mapping/cartography/2015/06/17/fun-with-graticules.html
There is also a relevant thread on the geotools developer mailing list,
interesting stuff there too.
About the usage issues, there are a few:
- Reprojection, right now the store generate lines made of two points,
and our reprojection engine still reprojects point by point, without on the
fly densification when a line is too long to be reprojected "as is". It's a
feature that I have in my backlog, but not sure if and when it's going to
be implemented. I think the grid module can densify, but to get good
results one would have to densify dynamically, depending on the zoom level
and target projection... which is a bit of trouble when you just give a
layer for anybody to use against the 5000 projections we expose
- Labelling, often people want the ordinate of the grid line shown at
the map margins, which is something we cannot easily do right now, although
it might be doable with a rendering transformation (intersect with the
rendering bbox, pad back from the border enough, add an attribute to give
the label vertical or horizontal orientation)
- Multilevel grids: often the maps require grids that are multilevel,
every 10 degrees depicted one way, and the others every one in a different
way
Now, I believe that all of the above issues can be solved via SLD and
rendering engine improvement with some extra effort, but they are not
exactly trivial. I guess that's why people have considered doing them as
decorations instead, and/or as DirectLayer.
All in all, I'd be favorable with just creating a grid store too, that's
something I'd been quite tempted to do myself, we should just explain to
the user base what the current limitations are
Cheers
Andrea
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