Tirmuncq

MEANWHILE, 5 MONTHS LATER... I just built a green-screen studio with 3 cameras at fixed positions. I want to use AF Designer (AFD) to create vector-drawn background scenes that replace green-screen in post. While they are the 'same' background, shot from 3 different camera angles, they nevertheless require 3 separate vector-drawn AFD backgrounds, as AFD doesn't currently handle perspective shift (perspective projection). My work-around has 5 cartesian transformations encoded into a Numbers spreadsheet: -- a 3D translation from the studio origin to each camera location; -- a 3D camera orientating z-axis rotation for each camera; -- a 3D camera orientating y-axis rotation for each camera; -- a 3D camera orientating x-axis rotation for each camera; -- a 3D perspective projection to a chosen 2D image plane (my background drawing). The spreadsheet allows me to enter 3D (x, y, z) coordinates for multiple points in world-space and read off their corresponding 2D coordinates, projected on an image plane (my drawing) at a chosen distance from each camera. In other words, I use the transformed 2D coordinates to reconstruct a common background scene from the angle and orientation of each camera. Q.E.D. When I came to draw the backgrounds in AFD, I first translated the ruler origin to coincide with my chosen origin in the studio. Perfect! So far, so good. Imagine my dismay though, when I noticed the y-axis was upside down (I found this thread while googling how to invert it). Cartesian axes constructed from the point of view of an image sensor located behind a camera lens have their place, but it's not in general use. Serif, we need axis inversion, school kids (future designers) all over the world are learning vector-space analysis based on Descarte's original 'right-way-up' axes. Meanwhile, I can work with AFD using the simple expedient of multiplying all my y-coordinates by -1. That isn't the problem. I can't routinely THINK upside down, that's the problem! Here's an example. I draw a brick wall being built on the origin of a document dimensioned in millimetres. Currently, it's 1000mm tall. So in AFD, the top is at the point (0, -1000, 0). Suppose its builder lays 4 additional courses of bricks, adding say 500mm to its height, I calculate the top at the point (0, -1000, 0) + (0, 500, 0). In AFD, it will be redrawn half as tall as it was and one third the height it should be. A trivial example, but it illustrates how real world assumptions promote calculation errors when using an inverted y-axis. AFD needs an 'Alice' tool that flips its world the right way up. Thanks. Tirmuncq, Nottingham