Question

Identify the point of light to cast the image in a perspective cylindrical projection:

• A. at a point diametrically opposed to the point of contact of plane
• B. at infinity
• C. centre of the generating globe
• D. at the point where the plane touches the generating globe

Hint:

If the projection is "Perspective" and "Cylindrical," always look for the light source at the "Centre of the Globe."

Answer 1

The Correct Option is C

Concept: Map projections are classified as "perspective" if they can be constructed geometrically by projecting light from a specific point through the globe onto a developable surface (like a cylinder)[cite: 236].

Step 1: Defining Perspective Cylindrical Projection.
In this projection, a cylinder is wrapped around the generating globe, touching it along the equator (the line of contact)[cite: 236, 251].

Step 2: Locating the Light Source.
For a standard Perspective Cylindrical projection, the "point of light" is placed at the exact geometric centre of the generating globe[cite: 242, 254]. The light rays pass from the centre through the features on the globe's surface and onto the cylinder[cite: 236, 251].

Step 3: Differentiating from Gnomonic/Orthographic.

• Centre of Globe: Perspective/Gnomonic property[cite: 242].
• At Infinity: Orthographic property (parallel rays)[cite: 240, 253].
• Diametrically Opposed: Stereographic property[cite: 238, 252].