Free Trimetric Projection Grid Generator

The isometric grid tool draws the popular one, because it is the cheap one. One scale means one ruler. The three axes sit at 120° apart on the page and the construction can be done with a 30-60-90 set square and nothing else. Every technical drawing office in the world could produce it, which is most of why it became the default.

Dimetric is the compromise. Two scales, still manageable by hand, and it lets you favour one face of the subject. ISO 5456-3 codifies a dimetric case at 7° and 42°, chosen so the resulting scales landed near workable ratios.

Trimetric had no such shortcut. Three angles means three scales, all irrational in general, and every measurement in the drawing had to be computed or read off a purpose-made scale. Before CAD, that cost was prohibitive for anything except a drawing important enough to justify it.

So the projection existed in the standards and was documented in every drafting textbook, and almost nobody drew it. The exceptions were mostly aerospace and automotive cutaways, where the subject's own geometry determined the only useful viewpoint and no convenient case fitted it.

Computers removed the cost entirely. A CAD package computes three scales as easily as one, and the moment the projection became free, trimetric views started appearing in exploded assembly drawings, technical illustration and product visualisation — anywhere the subject rather than the convention should decide the angle.

The defaults here place the three families at −12°, 33° and 78°. Those are 45° apart from each other, and at that spacing the view reads as natural rather than schematic: neither the flat symmetry of isometric nor the strong front-face bias of a low dimetric.

Choosing angles in practice starts with the subject's dominant face. Whichever face carries the information — the front of a machine, the top of a circuit board, the elevation of a building — should be presented closest to flat, which means the two axes bounding it should be shallow.

Then the third axis sets the apparent height of the viewpoint. Near 90° you are looking almost straight on; near 60° you are looking down. That single number changes the character of the drawing more than the other two combined.

A common mistake is setting all three by aesthetic instinct and then discovering the drawing has no readable face at all — every plane at a middling angle, nothing flat enough to carry detail. Decide which face matters first, then set the angles to serve it.

The other common mistake is forgetting the projection is not perspective. Nothing in the drawing gets smaller with distance, so a long object recedes without converging and can look, to an eye trained on photographs, like it is getting larger at the far end. That is not an error in your drawing; it is the well-known reversal effect of parallel projection, and every axonometric drawing has it.

The reversal is why axonometric works for objects and fails for spaces. A machine part drawn axonometrically is legible and measurable. A room drawn the same way feels wrong, because the eye expects the far wall to be smaller and it is not. That boundary — roughly, the size of a thing you could pick up — is a useful one to keep.

Historically the projection has a second life outside engineering. Oblique parallel projection has been the standard construction in Chinese and Japanese scroll painting for over a thousand years, and for a structural reason: a handscroll is viewed by unrolling it, so the viewer moves along the picture and there is no fixed station point for lines to converge toward. Parallel projection is the only construction consistent with how the object is used.

Twentieth-century architecture picked it up for a different reason. The axonometric came to stand for a way of thinking about buildings as assemblies of measurable parts rather than as scenes to be viewed, and the exploded axonometric became the signature drawing of a whole generation of architectural theory.

For drawing over reference, the workflow is the reverse of construction. Load the image, then adjust angles until the three families lie along the subject's own edges. Because you have three independent angles, you can match nearly any parallel-projected source, which is not true of the isometric or dimetric grids.

That makes this the grid to reach for when you are matching something rather than inventing it — an existing product line, a game's established look, a client's previous drawings. The others make you accept their convention; this one takes yours.

The density control applies to all three families at once, with each family's own scale applied on top. Set it by the smallest feature you need to place: if the feature is smaller than a cell, the grid cannot help you position it.

For a construction sheet, export raster at your paper size and 600 DPI and the printed lines will be genuinely fine rather than merely small. For a layer in a vector application, export SVG — every line stays a line, editable and re-colourable.

One property worth knowing: because the export is sized from the paper format rather than from your screen, the same workspace exported at A4 and at A2 gives the same construction at two sizes rather than two different constructions.

The grid draws over your image rather than exporting a fixed template because placement is part of the answer. Where the origin sits determines which of the subject's edges land on grid lines, and that is a judgement about the subject. The trimetric overlay page sets the family out, beside the rest of the perspective category. For the two-scale case the dimetric grid generator fixes the angles for you.

Everything runs in your browser. Images you load are never uploaded — there is no server for them to reach. The drawing, the transform and the export all happen on your own machine, which is a structural property of how the tool is built rather than a policy.