[mapserver-users] Backgrounds and Graticules in Pseudo-cylindrical Projections

[Paul Ramsey]

The way I would approach this would be to generate a physical
graticule. That is, an actual polygonal lat/lon grid on the spacing
desired and with vertex densification between the corners. The
polygons can then be added and projected, color filled for the effect
you want, and the outlines highlighted (or not) to form a graticule.

P

On Tue, Jul 14, 2009 at 5:42 AM, <winwaed at gmail.com> wrote:
> I am using MapServer to create some web maps using equal area projections.
> Most of these are pseudo-cylindrical, and I am currently using Mollweide for
> the initial development.
>
> This works fine and I even have it working with WMS to OpenLayers
> (OpenLayers and adding layers from different projections is a different
> kettle of fish, but I've asked that question elsewhere!).
>
> With a projection like this, a zoomed out map has two areas: projected
> space, and non-projected space. Ie. the projected globe does not take up the
> entire map "canvas".
> To me, this means we have two background colors: the background for the
> shapes in projected space, and the true background of non-projected space. I
> hope that makes sense?
> I'll try with a real world example. I have a layer that shows land masses.
> This is green. The mapfile is set to have a blue background (for the
> oceans). These are being drawn correctly, but the blue is also used for
> areas outside the projected globe.
>
> Is it possible to specify a different color (or "transparent") for the area
> outside the projected globe?
> The best idea I have is that I create a new layer of three shapes that cover
> the entire globe completely. This would be drawn as blue as the lowest layer
> in the mapfile, and the mapfile's background would be set to white. Is there
> a more efficient way?
>
> I would also like to add a geographic graticule (ie. meridians and
> parallels). I've tried the GRID definition in the mapserver map file, but
> this simply draws a cartesian grid in projected space. Can this be done in
> MapServer? I guess I could again solve this with a new layer of shapes.
> Otherwise it is OpenLayers (with a dev version of a graticule control, or
> more likely - write my own code)
>
>
> Richard Marsden
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