Representation of form, space and volume: perspective, proportion, structure and modelling
This domain tests whether a constructed drawing stands up: whether objects share one ground plane in a consistent space, and whether volume is modelled by a single coherent light logic. Perspective, proportion, structure and modelling are four checks to run on any drawing before detail is added.
Perspective conventions
- The horizon line is the viewer's eye level; it moves with the viewer, not with the object.
- One-point: a face is parallel to the picture plane. Two-point: a vertical edge is nearest. Three-point: for looking up or down tall forms.
- Vanishing points for horizontals lie on the horizon; verticals stay vertical in one- and two-point construction.
- Ellipses: the minor axis points toward the relevant vanishing point. A circle in the ground plane at eye level flattens to a line; the further below eye level, the more open the ellipse.
- Depth cues: overlap, relative size, height in the field, convergence, aerial perspective, cast shadows.
Proportion and structure
- Set a unit (the bottle's height) and measure everything in units by sighting along a pencil held at arm's length.
- Use plumb and level lines for alignment, and negative shapes to check intervals.
- Build from simple volumes (box, cylinder, sphere, cone); place cross-sections where forms change direction.
Modelling
- One light source. Name it and hold it for the whole drawing.
- Zones: highlight, light, core shadow, terminator, reflected light, cast shadow, contact shadow.
- Reflected light never exceeds the light side; the contact shadow is the darkest value and anchors the object.
- Hatch along the curvature of the form rather than smudging to fake tone.
Worked example
A cube with an upright cylinder on top, in two-point perspective. Reasoning: draw the horizon, choose two vanishing points far apart (close VPs produce violent distortion), construct the nearest vertical of the cube and measure its height, project the cylinder base as an ellipse with a vertical minor axis, then stack the top ellipse so that it opens less as it approaches eye level. With light from upper left-front, shadows fall right-back and the cast shadow joins the base. The cast shadow's direction must agree with the ellipses and the VPs, or the objects float.
Traps
- Shifting the horizon or the VP distance midway.
- Pointed ellipses, or identical ovals at every height.
- Multiple conflicting light sources.
- Reflected lights drawn as bright as the lit side.
- Outlining overlaps instead of letting the near object occlude the far one.