A Line at a Constant Height

A Line at a Constant Height

What this makes

Hand it a photograph and it comes back as contour lines — every line a closed loop at one depth, none of them crossing, none of them stopping in mid-air, with the spacing doing all the shading. Two fields.

You are given ONE photograph. Return ONE image: that photograph drawn as contour lines. Follow every line. Replace only the FIELDS block; everything after it is fixed.

First — do you have the photograph and the fields?

Say what this makes before you ask anything, in one or two sentences of their own words. Someone who has just pasted this has no idea what they are being asked for, and questions arriving cold are questions answered badly.

If no photograph is attached, stop and ask for one. This describes the form of a particular thing; there is nothing to slice without it.

If either field below still has braces around it, stop and ask. Put both questions in one short message, and show the example under each one so they can see the shape of a useful answer. Wait for the replies, then work. Never fill a brace yourself.

Ask in whatever language they are writing to you in. Translate the questions and the examples; do not make someone read English to tell you what they want.

If the photograph is attached and both fields are filled in, ignore this and carry on.

Fields — replace these two lines only

• What is nearest the camera, and what is furthest: {two points on the subject}
• How many lines between them: {a count}

The law everything else follows from

Everything about how the subject is drawn may change. Nothing about what is in it may.

The rendering becomes a set of slices. What is in the picture does not move: same subject, same angle, same arrangement, same framing, same relative sizes. It is that photograph, contoured.

A contour is every point at one depth

This is the whole rewrite, and everything below is arithmetic.

Imagine slicing the subject with a stack of planes parallel to the picture, evenly spaced from the nearest point named in the first field to the furthest. Each line in the drawing is where one plane cuts the surface. From that single definition:

• No two lines ever cross. A place on the surface has one depth, so it can be on one line only. A crossing is impossible, not untidy.
• No line branches. For the same reason: a fork would mean one point at two depths.
• Every line closes on itself or leaves the picture. A slice through a solid comes back round. A line that simply stops in the middle of the frame cannot exist.
• A line may be several separate loops where the plane cuts a shape more than once — either side of a nose, both sides of a handle. That is correct, and they still do not touch.
• Nested loops mean the surface is rising or falling toward that point. A small loop inside a larger one is a peak or a hollow.

If any two lines in the result touch, cross, merge or fork, the drawing is decoration.

Draw them from the inside out, one closed loop at a time

Work in the order the slices come. Start at the nearest point the first field names and draw the smallest loop around it. Then draw the next loop, enclosing the one you just drew. Then the next, enclosing that. Carry on until you reach the furthest point.

• Finish each loop before starting the next. Come back round to where you began. A line you have not closed is not a contour.
• A loop only ends early when it runs off the edge of the picture, and then it must leave the frame cleanly rather than fading out.
• Where the surface splits, one loop becomes two, and both of them close. They do not join and they do not touch.
• Never lift the pen in the middle of a form. If you find yourself drawing a short stroke that goes nowhere, you are hatching, and hatching is not what this is.

Spacing is the only shading

• Lines crowd where the surface turns away from the camera steeply — the side of a cheek, the shoulder of a pear.
• Lines open out where the surface faces the camera — a forehead, the flat top of a table.
• A surface exactly edge-on has lines so tight they merge into a dark band. That band is the silhouette, and it is the darkest part of the picture.
• There is no other shading anywhere. No grey, no fill, no hatching, no stipple, no gradient. Ink on bare ground.

The lines are all the same kind of thing

• One weight for all of them, because every line means the same thing. Do not thicken the near ones.
• Optionally, every fifth line is slightly heavier as an index line. If you do that, do it consistently across the whole picture.
• Lines are smooth and continuous, not sketched, doubled or furry.
• The count between the two named points is the count in the first field, and the spacing between slices is equal all the way.

What contours cannot say

• Texture is gone. Skin, hair, cloth, bark and glass all come out as the same lines. Do not draw a texture on top.
• Colour is gone, and so is the light. A contour drawing of a bright face and a dark one look the same.
• Small features become one small loop or nothing.
• The count of things stays right. Detail may go; objects may not.

Never

• Text, numerals, spot heights, a scale, a legend, a signature or a watermark anywhere, in any script.
• Lines that cross, touch, branch or stop in mid-air.
• Fill between lines, colour ramps, shadows, glows or a grid.
• A border, a frame, a map surround or a mock-up.
• A subject the photograph did not contain.

What it should read as

A map of a thing that is not a landscape — and you should be able to see the shape from across the room without a single tone in it.