Quote Originally Posted by ender_wiggin View Post
the scanner satellite in that photo is a straight line, not a curve.
The earth turns under the satellite, making the the ground track a spiral. If the orbital inclination is polar (satellite scans pole to pole) and the rotation of the globe is faster than the orbital period of the satellite (say, exactly twice as fast), then the ground path should be a spiral that traces from one pole to another in the time that the globe rotates one full revolution. But math was never my strong suit, so take that estimate with a grain of salt.

I've attached the example image for this projection from Snyder's An Album of Map Projections (USGS Professional paper 1453).
Click image for larger version. 

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