Coordinates and units

A T3D volume is a 3D texture of width × height × depth voxels. Operators address it in normalised coordinates rather than voxels, so a network keeps its shape when the resolution changes.

Sizes and positions

Positions are fractions of each axis's own extent: a Translate of 0.1 moves content a tenth of the width along X, a tenth of the height along Y and a tenth of the depth along Z. That holds in every operator with a Transform page, with or without Aspect Correction (measured in a 128 × 64 × 32 volume: 12.8, 6.4 and 3.2 voxels).

Aspect Correction (on by default wherever it exists) is about shape, not position:

• In the shape generators it measures sizes (Radius, Softness, a box's Scale) in units of the volume's width on every axis, so a sphere of radius 0.1 is 26 voxels across along X, Y and Z of a 128 × 64 × 32 volume. Off, each axis runs across one unit whatever its voxel count, and the sphere stretches with the volume (26 × 12 × 6 voxels).
• In the composers and Transform it rotates in undistorted space: a bar rotated 90° keeps its length. Off, rotation shears a non-cubic volume.

Where the origin is

Two conventions exist, and they differ only in where the origin sits:

Operators	Origin	Range along X	Pivot default
Shape generators: box, sphere, torus, tube, sdf, metaball, fractal	volume centre	−0.5 to 0.5	0 (centre)
Composers and filters with a Transform page: add, subtract, multiply, difference, composite, cross, displace, fit, transform	corner	0 to 1	0.5 (centre)
noise	corner	0 to 1	0 (corner)

The default pivots put rotation and scale about the volume's centre everywhere except in noise, where they act about the corner at the origin.

Voxel i along an axis of n voxels has its centre at (i + 0.5) / n. Operators sample their inputs at those normalised positions with the filtering set by Input Smoothness, so inputs of different resolutions line up by extent, not by voxel index.

Transform parameters

The Transform pages follow TouchDesigner's conventions: Transform Order and Rotate Order as on a Geometry COMP's Xform page, rotations in degrees. The transform moves the content: a translate of 0.1 in X moves the shape, or the overlay in a composer, one tenth of the volume's width towards +X.

In world space

volume and surface draw the volume as a box one unit wide, with the volume's proportions, centred on the origin of their own component. Transform the operator to place it in a scene.

Volumes made from geometry need to go back to where the geometry was. The operators that build a volume from, or move content through, world space export that mapping: geo_to, point_cloud, metaball, sprinkle and advect. Point the T3D Transform Reference of volume, surface or voltrace at one of them, and the volume is scaled and placed so it lines up with the source geometry. advect has the same parameter, to move particles through a volume in world space.