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Composite Ap Q & A

Here are some of the more common composite application-related web searches that point folks to IDVUX…

Q: why is virtual earth so dark

A: I have been asked this question often by clients.  I assume the person wondering about this is referring to the Aerial style at global zoom levels; which is quite dark.  I don’t know why it is as dark as it is -maybe to visually promote the white text labeling?

The source is a composite of cloud-free sections of satellite imagery courtesy the NASA Earth Observatory.  The Satellite platform used is NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS).  How did even NASA manage to snag a shot of Lansing, Michigan, not draped in clouds?  I don’t know.

I see this imagery used by just about all of the big map-service providers at the higher zoom levels, and the Virtual Earth implementation of this imagery is quite a bit darker than the rest, and it does appear as though the darkening is intentional.  Below is a comparison of the Caribbean as seen in Virtual Earth (top image), and the same screenshot with the brightness and saturation bumped up (bottom image).  It starts to look a lot like the other guys’.  In the brighter version you can see that there is even a little coastal shelf bathymetric indication in the NASA imagery.


Q: silverlight virtual earth

A: IDV has recently released a simple public map viewer that has been built from the ground up in Microsoft Silverlight.  This is the first release in a series of Silverlight demos that will have progressively more features and doodads.  Up next? Draw Tools!

A snapshot of the geographic drawing tools in the next release of the IDV Silverlight Virtual Earth demo.


Q: 3d mapping projection

A: Google Earth requires their streaming overlay imagery to be in the Equirectangular projection (a.k.a. Plate Caree or any of the spelling variants and mis-identified as simply WGS1984, Lat Long, or unprojected) in order for it to drape correctly.  Virtual Earth 3D uses their 2D quad key tiled image set and warps it (to equirectangular) non-linearly over their sphere.  More info here: http://idvux.spaces.live.com/blog/cns!2EB6AAF6C3AC1EBE!177.entry


Q: silverlight 3d earth globe

A: Silverlight does not support 3D yet.  But it would be awesome if it did someday.


Q: How does water comes into our flat

A: Somehow the Baidu search engine pointed this unfortunate person to IDVUX.  Anyways…the water could be getting into the flat in any number of ways, including poorly sided exterior walls or a roofing material that has failed or enables water to pool.  If you are the topmost floor of your building, then you might have a roof that is collecting or damming water to the point where it is able to flow over the sealed or staggered roofing material.  More likely, though, a tenant above you has a malfunctioning plumbing system.  You should call your super as soon as possible, as dampness or repeated inundations can cause the structural materials of your flat to weaken, or worse, it could facilitate a mold problem -which can have serious and acute health consequences.


John Nelson / IDV Solutions / john.nelson@idvsolutions.com


3 responses

  1. Christopher

    Q: How does water comes into our flat what?
    Flat tire
    Flat pancakes
    Flat file
    Flat stomach…
    Those brits, using a one-syllable when a three-syllable one is so much better (apartment).

    May 30, 2008 at 12:29 pm

  2. Unknown

    Q: How does water comes into our flatWater comes into my flat via pipes.

    May 30, 2008 at 12:49 pm

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