2D pixels into 3D point cloud?

How do I convert 2d isometric sprite into a 3d model?

Here is an example of two complicated Scheme function, for translating between isometry and view coords. There is no need to know how they were derived to use them. They just work!

(define (map-to-view xy)
  (let ([x (vector-ref xy 0)]
        [y (vector-ref xy 1)])
    (vector (- (* x (/ tile-w 2)) (* y (/ tile-w 2)))
            (- (* x (/ tile-h 2)) (* y (/ tile-h 2))))))

(define (view-to-map xy)
  (let ([x (vector-ref xy 0)]
        [y (vector-ref xy 1)])
    (vector (/ (+ (* y tile-w) (* x tile-h))
               (* tile-w tile-h))
            (/ (- (* y tile-w) (* x tile-h))
               (* tile-w tile-h)))))