Hi Linda,
> I guess I am just an idiot but I just don't get it. I really appreciate you
> taking
> the time to try and explain but I just don't get it.
I teach MSc students in GeoInformatics that still don't get it, so don't feel
embarrassed. It's just that 'scale' and 'projection' are sometimes hard to get
to grips with.
> Yes I want a world map.
> Then when they get down to a certain resolution I want to display UTM.
> What would be really cool is if I could control the box at that level too.
> It needs to be 1200 UTM meters square, 2400 UTM Meters square and
> 4800 Meters square for the zooms.
This is part of your problem. You cannot expect to use data that is useful for
a very large scale (4800 msq in UTM on a screen boils down to something like a
1:25000 scale) to also be useable for a small scale world map (on screen
something like a 1: 200000000 million scale). That's just plain impossible.
Mapping sites like Google Maps use diffferent datasets for different scale
ranges, you will have to do that too...
> But if I use a world map it is in either spherical mercator or lat/lon. So
> right now I am hiding and showing a layer. Taking the lat/lon converting
> to UTM when they get to that level and returning that image.
Google Maps and co. do exactly that: Use latlon until a certains cale and then
switch to projected meter maps.
> slow and it just isn't working right. It would be easier if the entire map
> was
> in something like meters that I could go directly to UTM without the lat/lon
> stuff in the middle.
The slowness is likely because of you using the same data set to have both
types of maps and doping re-projections all the time. You'll have to use
pre-made datasets for the different scale levels for decent performance.
> The UTM image is just not the same image as the lat/lon
> image. Even though the coordinates are directly converted. I am so
> frustrated.
Of course they are not the same. Projection of a spherical object (Earth) to a
flat cartesian object (projected map) always will introduce distortions.
Imagine peeling an orange and flattening the skin. It will distort (and
probably break).
> I need a road map.
So make yourself one :-) But don't try to do it from a world dataset. Or maybe
better: use an existing road map, where people have done the hard stuff for you
already. Can you use Google Maps as a background layer in your OpenLayers
stack? If you need the actual road DATA, you could consider the free
OpenStreetMap (openstreetmap.org <http://www.osm.org/> ), although their
coverage is not so good for some parts of the world. Otherwise you might have
to buy some data from teh likes of NavTech or TeleAtlas...
--
Barend Köbben
International Institute for Geo-information Sciences and Earth Observation
(ITC)
PO Box 6, 7500AA Enschede (The Netherlands)
ph: +31-(0)534874253; mobile: +31-(0)622344955
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