linda.rawson at gmail.com
Sun Sep 30 17:57:17 EDT 2007
You are dead on. He wants his panning to be different based on where he is
I am using the WMS service from Nasa and then I am layering a single tile
image when they get to a certain resolution. So basically their API offers
me a way to pass in an Upper Left lat/lon and lower right lat/lon and it
returns an image. I can pass in projection as well.
My map provider is GEX/Digital Globe but their crack at an
openlayers solution is not working for me. If I didn't need markers, line
features, and any different resolutions it would work fine as a navigation
layer. It is full of bugs. It is not a WMS service but their own layer.
They must be in the middle of their merger because they are not very
Thanks for the information. It is SOOO helpful.
On 9/30/07, Christopher Schmidt <crschmidt at metacarta.com> wrote:
> On Sun, Sep 30, 2007 at 01:30:14PM -0600, Linda Rawson wrote:
> > I think I can get this one but if someone has a formula to help me that
> > would be great.
> > Basically he uses the panning tool. The north, south, east, west
> tool. So
> > when he goes east he does not want to evenly go to the next square. He
> > wants to go to the next square based on a sphere. If he was on the
> > then the pixels would be correct. But if he is in say Canada he wants
> > panning tool to go to the next square in the sphere. I hope this is
> > sense.
> Okay, I think I get it.
> The world is a kinda-spheroid like thing. The default OpenLayers
> projection is a lon/lot geographic coordinate system -- this means that
> 50 pixels north is 50 * map.resolution degrees north. However, what
> number of *meters* that is on the ground is variable, based on where the
> lat/lon are.
> So, in order to make the spheroid world a 2D plane, we 'project' it. The
> lon/lat geographic projection is just one option here -- others are, for
> example, mercator, or peters equal area, etc.
> It sounds like the person you are talking to wants a projected map.
> Depending on the type of things this person cares about, this may be
> easy or hard.
> http://openlayers.org/dev/examples/spherical-mercator.html is a
> set of projected maps. You can see that the WMS service is providing
> data not according to lat/lon, but according to projected units. To the
> user, it doesn't really make any difference, if they don't see the units
> -- they just know that they go up, and as they go up, the amount of
> latitude/longitude they go up by every time they hit the button is
> different, instead of the same.
> It's not really clear to me who 'the map providers' are in this case.
> Does he or she mean Google? If so, then the sphericalMercator support in
> 2.5 is probably just the kind of thing he is looking for, as it will let
> you lay images on top of these and tile them properly. If the customer
> is talking about some other data provider... well, it's hard to know
> what exactly he (or she) means.
> Perhaps with a bit more information about the scenario you are exploring
> would be helpful here.
> > I create the image based on the lat/lon coordinates passed to me with
> > layers. The mapping service I use just needs the upper left and lower
> > corners to return the images.
> Are you just using one layer? Where is the image coming from? Do you
> have a commercial base layer? something else?
> Christopher Schmidt
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