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Geometrical algorithm

Posted on 2002-03-20
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Last Modified: 2012-05-04
Can anyone provide me with an example of an algorithm to do the following conversion:

Input:
   Latitude / longitude coordinate on earth's surface
   Zoom level (from full world to a few miles across)
   X/Y pixel width of PC screen

Asusming this lat/lon point on earth is being viewed form a point in space perfectly Normal to the earth's suface:

Output:
   The X/Y point on the screen that the given input Lat/lon point maps to, given the above input data for zoom level and screen resolution.

I would also need a way to detremine if the lat/lon point is on the visible or hidden half of the earth (this is easy), and if hidden, figure out the last visible x/y point on the path from the previous visible point to the hidden point (more difficult).

Basically looking to map the spherical coordinates to rectangular coordinates.

Jeff
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Question by:jeffs1
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Expert Comment

by:sateesh_babu
ID: 6885293
Why don't you come up with an small pseudo code or algorithm, and them ask about it rather than putting the homework assignment directly.

Babu
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Expert Comment

by:cookre
ID: 6887250
What sort of projection?
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Author Comment

by:jeffs1
ID: 6894606
If I were to come up with the algorithm, I would be answering my ownb question... I cna do this, but I was hoping to take advantage of someone elses's experience here who make have done this already...

I am not looking for any particular projection (as in the paper world)... I have described above all necessary input criteria for the algorithm... just looking at the earth from a point in space normal to the surface of the earth.

Jeff
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Expert Comment

by:ozo
ID: 6894644
"Just looking at the earth from a point in space normal to the surface of the earth."

Does it matter which point in space?
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Author Comment

by:jeffs1
ID: 6894657
Points in space along a vector "Normal" to the surface of the earth are all on a single line from the earth to infinity.  The point along the line that you are at is determined by the zoom level.
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by:cookre
ID: 6894766
One presumes two input coordinates were intended - the stated observation point and the implied query point.

Also, it seems to me as if altitude IS needed.  After all, there's lots more below the horizon at 10km than at 1000km.
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Author Comment

by:jeffs1
ID: 6907227
Yes altitude is necessary... I was calling it Zoom level, but input is the same...
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Expert Comment

by:deighton
ID: 6925085
you also need to take 'angle of vision' into account, i.e. what proportion of a persons vision the pc monitor represents.
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by:modulo
ID: 7845257
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