[Geoserver-devel] Map grid overlay

I don't yet have a detailed proposal, but I'm considering doing an "map grid
overlay", so that you can take a base map and overlay a standard grid (like
MGRS or GARS), which is mostly transparent and has opaque or translucent
graticule lines.

The idea is that there wouldn't be an underlying data store of real map data,
its just a layer that you can turn on for "mash-up" style uses. It would have
some parameters (like how it scales in / out, colour, transparency) and
probably some per-layer configuration.

Now a grid would probably be better done as a client side thing (so
OpenLayers, Leaflet), but sometimes the client isn't some nice web based JS
thing, its a thick client that can get WMS...

Any suggestions for whether that is achievable without a fake datastore, or
other things I should look at?

Brad

There is an implementation of grid in geotools already - you could make it a fake datastore (using connection parameters to define the grid).

WMS also has the concept of WMS Decorations which would be a better fit for your workflow.

We have also introduced the idea of “direct draw layers” for the GeoTools renderer in the hopes of moving the WMS Decoration functionality closer to where the action is (and thus not always drawn on top).

···

Jody Garnett

On Thu, Oct 16, 2014 at 3:24 PM, Brad Hards <bradh@anonymised.com> wrote:

I don’t yet have a detailed proposal, but I’m considering doing an “map grid
overlay”, so that you can take a base map and overlay a standard grid (like
MGRS or GARS), which is mostly transparent and has opaque or translucent
graticule lines.

The idea is that there wouldn’t be an underlying data store of real map data,
its just a layer that you can turn on for “mash-up” style uses. It would have
some parameters (like how it scales in / out, colour, transparency) and
probably some per-layer configuration.

Now a grid would probably be better done as a client side thing (so
OpenLayers, Leaflet), but sometimes the client isn’t some nice web based JS
thing, its a thick client that can get WMS…

Any suggestions for whether that is achievable without a fake datastore, or
other things I should look at?

Brad


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On Fri, Oct 17, 2014 at 12:24 AM, Brad Hards <bradh@anonymised.com> wrote:

Any suggestions for whether that is achievable without a fake datastore, or
other things I should look at?

Following up with Jody, I see three ways:

* Fake datastore, the most visible downside of this approach, that I see,
  is that you'd have to play with styles to get what you want,
  and might need a rendering transformation if you need to place
  the labels at the map border. But it also has upsides, since it's a
  true data source you could use it for WFS (someone in need of a
  grid to download) and WPS (compute stuff over a regular subdivision)

* Map decoration like Jody suggested. Downsides, it's not a WMS layer
  anymore, it's something that you have to configure as an admin, and
  include it into the map output by adding a vendor parameter to
  choose the desired layout, so it won't work with shrink wrapped tools

* The "high path" would be to roll a new type of Layer in the configuration,
   and teach the whole GeoServer how to use it. See the work that was
  done, back then, to add WMS cascading as its own custom layer.
  The new layer could wrap what Jody's DirectLayer, and could be
  made extensible to allow any kind of direct layer to be configured (grid,
  or otherwise).
  The minimum workable set here would be to add it to the configuration,
  persistence, REST config, and WMS subsystem.

I think all the three paths would be welcomed, of course the last one, the
fancy one, could open more extensibility for the future... but it's also
quite
a bit more work I'm afraid.
To give you a reference, when I added WMS cascading to GeoServer,
with a WMS client already available in GeoTools, I had to work for five
days like a madman, no distractions, some overtime (and back then
there was no policy to add tests for everything, now there is).

Cheers
Andrea

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