mehesb: Convergence Control by Giant Horizon

A new teaching help in architectural freehand drawing

Key-words: extreme oblique line, framing cubic grid, giant horizon, linear perspective, oblique line of in-between, Vanishing Points’ Distance (VPD).

At the beginning of teaching architectural freehand drawing we are dealing with basic phenomena of linear perspective: convergence, foreshortening and hiding. The training of object and space drawing is based on observation. The role of a structural shell absolutely needed in these items is generally played by an enveloping cubic grid.

Reality’s parallel lines seem to converge in perspective and run toward vanishing points. These vanishing points happen very often to fall outside the paper’s surface. Forcing vanishing points to remain inside is a typical error. Being the consequence of our view point and chosen object size, the distance between vanishing points can’t be set in advance [1].

We should control the central cube’s credibility first of all with our own eye’s compass [2].

For objectively controlling the converging parts of the structural grid hereby I offer my new teaching help baptized Giant Horizon. The following steps show how to use the tool:

1 - Open air experiment with the map outfitted with an elastic cord. The wings can be widely out folded.

2 - While opening the map the rubber cord stretches itself and marks the Giant Horizon.

3 – The horizon is expanding. Fitting drawing’s horizon to map’s horizon, we slip the drawing to be controlled under the rubber cord.

In order to find even the remote vanishing point within the reach of the expanded horizon, we ought to start in suitable work zone. With a little practice the position of central cube’s vertical edge compared to the map’s halving axe can be evaluated in advance. This matches the proportion of central cube’s lateral planes. In symmetric (diagonal) position it can be just at map’s ridge.

4 – Approaching catch of extreme oblique lines. We are hanging the rubber cord on a pin stubbed into the farthest cube corner related to the horizon. Now the rubber cord’s arms are approximately catching the oblique lines.

5 – Précising of extreme oblique lines. In two more steps we accurately cover with rubber cord’s arms the extreme oblique lines which point toward vanishing points on the horizon. We realize the precise mark out of vanishing points by the help of pins.

6 – Oblique lines of in-between are to be compressed between extreme oblique lines and the horizon. Knowing the position of vanishing points we may control all of them.

To set map’s dimensions I was looking first for largest possible vanishing points’ distance occurring on regular A/3 sized drawing paper. In an open air experiment, sketching an almost parallel positioned 30 cm high giant cube with floor-line horizon, its remote vanishing point fell to 5 m off vertical scale. Generally dealing with smaller (third-sized of this) cubes in traditional object drawing subject, a 2 meter sized basic plate seems to be appropriate for teaching goals. Folded together as a map, it remains easily transportable.

In case of extreme VP-distance let us halve the cube! Let us directly work with diagonals’ vanishing points!

Exercise: Let us fix the vanishing points’ distance in advance and let us determine the biggest possible (still credible) cube’s value! [4]

Summary

Beside objective and convincing structural control, the convergence controlling teaching help called Giant Horizon has an opinion shaping effect, too. It induces us to consciously identify our own horizon in time. As a precondition we have to determine the horizon within our own drawing. It educates us to handle framing cubic grid’s related edges as pairs.

It habituates us to group in bundles reality’s parallel edges, which converge in perspective.

The Giant Horizon is adequate for controlling structural lines running in different planes as well [3].

Using the teaching help we may spectacularly demonstrate how an originally quadratic corner of a tower’s slab is transforming into a single line on the horizon in perspective.

While spanning along the nearest vertical edge with a pin marking the height of horizontal square planes, the rubber cord hang on it produces in row enlarging obtuse angles of perspective distortion.