Projection specification for the reference map

[havard.tveite@…]

Suggestion: Allow a PROJECTION object in the REFERENCE MAP object
    (and perhaps also a new attribute OUTLINEACCURACY [low | medium | high]).

There is currently not a possibility to describe the projection for the
image in the Reference Map Object. Here in Norway, we use many different
projections, depending on the main area of interest (most used is
UTM32-36, NGO I-VIII).
It would be very useful to be able to use the same (raster) reference map for
all these projections. I do not want the reference map to be projected (this
will generally result in ugly reference maps!).

It would therefore be very useful and practical to be able to use different
projections for the reference map and the main map.
This would, of course, in most cases lead to non-rectangular
outlines on the reference map, so one would have to determine
an appropriate level of detail for the outlines (from linear
interpolation between the four corner points to a smooth
rendering of the exact boundary curves). The lowest level
of detail would imply four coordinate transformations while
a high level of detail would lead to lots of coordinate
transformations (and hence some extra overhead costs).
If we do not want to determine a predefined level of detail
for the rendering, we would have to introduce a parameter
for this. e.g OUTLINEACCURACY [low | medium | high].

The only effect I believe this would have on other elements
is that "EXTENT" in the reference map object would have to
be specified in the reference map coordinate system.

Answer from Stephen Lime (Wed, 07 Aug 2002):
... This should be added as a feature
request to Bugzilla so that the idea
is not lost. That said, there are other possibilties:

There is nothing that says that you can't use two different MapServer
applications on the same page. In 
reality you can mimic a reference map using a second mapping
application. If you look closely at our
Recreation Compass (http://www.dnr.state.mn.us/maps/compass.html)
application you'll see we have 
done just that. I wanted a reference map that would display a filled
box sometimes, a marker symbol
when the was too small, and nothing when the box was too large (eg. you
didn't need the reference map).
Prior to 3.6.1 you couldn't do this the the reference map object. The
solution was to use a second
little application. Worked like a charm and required on a small bit of
javascript. I would imagine you could
do the same thing with a reference map in a second projection. You'd
just have to use lat/lon as a go
between coordinate system. Worth a look if this is functionality you
need ASAP.


woodbri@swoodbridge.com (Wed, 7 Aug 2002):
Interesting that this just came up because I ran into this same 
problem just yesterday. The problem I had was not so much wanting the 
reference map to be projected, but the fact that I had created it in 
one projection and had later changed the mapfile's projection 
parameter to a different projection. If the reference map is not 
created in the same projection as the mapfile projection is does not 
work. It would be nice to be able to say WHAT projection the 
reference map was made in so you don't have to recreate the reference 
map if you change the projection parameters on the mapfile.

[dmorissette]

We've talked about this several times at our end as well.  There is definitely 
no time in 4.0, but we should revisit this later, maybe in 4.1

[dmorissette]

*** Bug 409 has been marked as a duplicate of this bug. ***

[dmorissette]

For the record, here is what Paul Spencer had written in bug 409:
---

I would like to suggest that the Reference object be extended by the addition of
an optional Projection object.  The intention is to define the projection of the
reference map image so that applications can support viewing maps in different
projections while maintaining the same keymap.

The extent of the reference map would then be defined in the coordinate
system/units of the reference object's projection.  If no projection is defined,
then it is assumed to be in the projection of the map as a whole.

When the projection of the reference map is not the same as the projection of
the map, then the map's extents would be reprojected into the reference map's
projection before being drawn.

It would also be desirable to be able to draw non-rectangular bounding boxes on
the reference map when the projection has changed.  This could be done by
reprojecting points around the original bounding box and 'connecting the dots'.
 This could use a pre-defined number of samples or be controlled via a new
attribute of the reference map that would specify the number of samples to take
around the box.

This addition would slow down reference map generation, so it is important that
this functionality only be triggered if a projection is defined and the
projection is different from the map's projection.

[dmorissette]

*** Bug 432 has been marked as a duplicate of this bug. ***