solidcraft/docs/point-clouds.md

Point clouds

A point cloud is scanned points kept in the design as a reference to model from (#5151): a lidar or SLAM map, a photogrammetry result, a part from a handheld scanner. It is drawn as dots in the viewport, depth-tested with the bodies, and never becomes a body; nothing in the timeline depends on it.

Files

Extension	What is read
.ply	ASCII, binary little-endian and binary big-endian PLY: the vertex element's x, y, z (any numeric type) and its red, green, blue when present (bytes, 16-bit or 0…1 floats). Every other scalar vertex property (intensity, a class, a time…) is kept, by its name in the file, to colour and filter the cloud by; it is whole-numbered when its type is an integer. The edge element (vertex1, vertex2) and the face element (vertex_indices, a face as a fan of triangles) become segments and triangles between the points, with their own properties. Other elements are passed over.
.xyz, .pts	Text, a point per line: x y z, optionally followed by r g b (six numbers) or by an intensity and r g b (seven or more, as PTS files write it). Spaces, tabs, commas or semicolons separate the numbers; # and // start comments; a PTS file's first line (its count) is skipped.

A PLY file with faces can also be inserted as a mesh body with Insert Mesh (file.insert_mesh), which makes it solid geometry rather than a reference.

Point cloud files say nothing about their length unit. units (mm, cm, m, in, ft) says what it is; the default is millimetres, as for every other import. Lidar and SLAM maps are usually in metres. The unit can be changed afterwards (Browser › Point Clouds › Edit Point Cloud, or pointcloud.edit with units): the points are scaled from the unit they came in as.

Colours

Color By in the Edit Point Cloud card (or color_by) says how the points are coloured:

• file (the default): the file's colour of each point, grey when it has none.
• single: one colour (color) for every point.
• height: a ramp by design Z, blue low through cyan, green and yellow to red high. It runs between two heights (color_range, mm). By default they are worked out from the points: all but the lowest and highest 2 %, so a few stray points don't flatten the ramp.
• any property's name (x, y, z or one of the file's): the same ramp over the property's values or, for a whole-numbered property, a palette of ten colours (its value modulo ten; negative values grey). By default the ramp runs exactly over the values the property takes on the points every filter keeps, so filtering re-spreads the colours over what is left.

A ramp's range is a range track in the card; touching it sets the range and turns Automatic Range off, and ticking the box (or a double click beside the range) gives it back. color_range: null does the same from a command.

A whole-numbered property may name its values with a PLY comment, property: 0 name, 1 other name, -1 none (for example comment role: 0 outer wall, 1 inner wall). Coloured by it, the card shows a legend, a swatch and a name per value; clicking a name shows or hides that value.

Edges and faces

A cloud read from a PLY file with edges or faces draws them between its points: triangles filled, segments as lines or, when they have width and height properties, as beads of that stadium cross-section (a tube when the two are equal), meeting mitred where one runs into the next. Points no segment or triangle ends on stay dots, of the cloud's point size. A point that can't be read (not a finite number, or out of range) is left out with a warning, and so are the segments and triangles that end on it.

A property on the points varies along the segments and across the triangles that meet there; one on the segments or triangles is constant on each. Colours follow the same rule, and a range filter cuts an element exactly where its value crosses an end of the range, so a filter on a time property replays a path as it was drawn. A range track weighs each element by its measure, each kind over its own total: a dot counts 1, a segment its length, a triangle its area.

Filters

A filter keeps the points whose property lies in a range (both ends included) or, for a property with named values, is one of a set of values. Only what every filter keeps is shown; a cloud has at most 8 filters, and the view applies the first 4. Filter by in the card adds one over a property's whole span (or with all its named values); × removes it. Filters change what is drawn, never the points the design holds.

Range tracks

Each range filter, and a ramp's range, is edited on a track, as a range is in an audio editor. The track draws how much of the cloud lies at each value: a histogram of the property over what the other filters keep, stacked by colour, so it is also the colour legend. A thin strip above it shows the property's whole span, with the part the track shows framed.

• Drag an end or the band between them to move them; drag elsewhere to draw a new range. Shift-click brings the nearer end to the pointer.
• Double-click the band to fit the track to it; double-click beside it for the whole span. The wheel or a pinch zooms around the pointer, a sideways scroll pans, and dragging in the strip moves the framed part.
• An end snaps to a value where the colour changes when no other change is near at this zoom; a whole-numbered property's ends snap to whole numbers. ⌥ moves ten times slower, without snapping.
• Once the track is touched, ← and → bring the part touched last to the previous or next colour change (one pixel with ⌥, or where there is none).
• Start, End and Length are fields too; Length keeps the start. A value typed with a sign is relative: +30 moves it by 30.
• ▶ Play (or Space) moves the part touched last across the track in 20 seconds: an upper end grows the range, the band slides it, a lower end wipes it. The track follows it, and an automatic colour range follows it too. Touching the range stops it.

Size

A cloud keeps at most max_points points (5,000,000 unless asked, at most 20,000,000); a larger file is thinned evenly, one point in n, and the result says how many were kept. Thinning would cut a file's edges and faces, so a thinned file leaves them out, with a warning; raise max_points to keep them. A cloud holds at most 20,000,000 segments and as many triangles. Files up to 1 GiB are read. The points are stored single precision relative to the cloud's first point (kept double precision), so a scan far from the origin keeps its detail; they travel inside the design file as a binary part (12 bytes a point, 3 more with colours).

Commands

• pointcloud.insert — path; name?, units?, max_points?, center? (move the middle of its base to the origin), point_size? (pixels), color_by? (file, single, height or a property's name), color? ([r, g, b] 0…1; alone it means single, null means file), color_range? ([low, high], or null for the automatic range; height_range is the same), filters? ([{"property": …, "range": [low, high]} or {"property": …, "values": [whole numbers]}], or null for none).
• pointcloud.edit — cloud (id or name); name?, visible?, point_size?, color_by?, color?, color_range?, filters?, units?, matrix? (a rigid placement, as occurrence.move takes it).
• pointcloud.delete.
• pointcloud.list — each cloud with its segment and triangle counts, its properties (name, whole-numbered or not, span, named values), its filters and its ramp's range as drawn (color_range).
• doc.open opens a point cloud file as a new design holding it; dropping one on the window adds it to the open design.

Example

{"command": "pointcloud.insert", "params": {"path": "glim-points.ply", "units": "m", "color_by": "height"}}
{"command": "pointcloud.edit", "params": {"cloud": "glim-points", "color_by": "intensity", "filters": [{"property": "z", "range": [0, 2500]}]}}