[OpenLayers-Users] Orthorectifying

[Linda Rawson]

You are dead on.  He wants his panning to be different based on where he is
at.

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
helpful.

Thanks for the information.  It is SOOO helpful.

Linda Rawson

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
> equator
> > then the pixels would be correct.  But if he is in say Canada he wants
> to
> > panning tool to go to the next square in the sphere.  I hope this is
> making
> > 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
> open
> > layers.  The mapping service I use just needs the upper left and lower
> right
> > 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?
>
> Regards,
> --
> Christopher Schmidt
> MetaCarta
>
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