A fixed observation unit
In a fictional still-life exercise, a bottle is chosen as one observed height unit. From a fixed viewing position the box is half that height and the bottle width is three tenths of its height. The student chooses to represent the bottle 20 cm tall on a 42 cm-wide sheet. The brief asks for a right-hand third position and a consistent central-perspective sketch of the box. A classmate changes viewing distance between measurements, while another multiplies by an unexplained factor taken from a different exercise. No absolute real-world height of the bottle is supplied, so the sketch is a proportional observation model rather than a certified scale drawing of a measured object. The task asks students to preserve the stated ratios and distinguish this comparison from a dimensioned technical plan.
1. Calculate the represented box height, bottle width and right-hand third coordinate.
Read the worked answer
The box is 10 cm high and the bottle 6 cm wide. The right-hand third is 28 cm from the left edge, or 14 cm from the right edge. No additional factor is required. Keep the observation unit and viewpoint fixed to preserve the measured ratios, and use coherent convergence for the box rather than mixing a parallel-projection construction into the same chosen central-perspective model.
2. Explain why the fixed viewpoint and declared perspective matter.
Read the worked answer
The box is 10 cm high and the bottle 6 cm wide. The right-hand third is 28 cm from the left edge, or 14 cm from the right edge. No additional factor is required. Keep the observation unit and viewpoint fixed to preserve the measured ratios, and use coherent convergence for the box rather than mixing a parallel-projection construction into the same chosen central-perspective model.