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Sections, slices and drawings

Many uses of a 3D model are flat: the layers a 3D printer or a laser cutter makes, a cross-section through a part, a technical drawing with hidden edges dashed. bitbybit.occt.operations cuts shapes for all of them.

Slices​

slice cuts a solid into parallel layers along a direction, every step model units, like a loaf of bread. Each layer is the flat section where a cutting plane meets the solid, and all of them come back in one compound. sliceInStepPattern uses a repeating pattern of gaps, and sliceByFrames cuts with the plane of each frame you give it, at any angle.

Here a sphere is sliced every half unit along Y:

Bitbybit Platform

A sphere cut into layers in Rete

rete logoRete
Script Source (rete)
{
  "id": "rete-v2-json",
  "nodes": {
    "sphere": {
      "id": "sphere",
      "name": "bitbybit.occt.shapes.solid.createSphere",
      "customName": "sphere",
      "async": true,
      "drawable": true,
      "data": {
        "genericNodeData": {
          "hide": true,
          "oneOnOne": false,
          "flatten": 0,
          "forceExecution": false
        },
        "radius": 4,
        "center": [
          0,
          0,
          0
        ]
      },
      "inputs": {},
      "position": [
        40,
        40
      ]
    },
    "slice": {
      "id": "slice",
      "name": "bitbybit.occt.operations.slice",
      "customName": "slice",
      "async": true,
      "drawable": true,
      "data": {
        "genericNodeData": {
          "hide": false,
          "oneOnOne": false,
          "flatten": 0,
          "forceExecution": false
        },
        "step": 0.5,
        "direction": [
          0,
          1,
          0
        ]
      },
      "inputs": {
        "shape": {
          "connections": [
            {
              "node": "sphere",
              "output": "result",
              "data": {}
            }
          ]
        }
      },
      "position": [
        460,
        40
      ]
    }
  },
  "modules": {}
}

Each slice is a face: extrude it by the thickness of your sheet and you have the parts of a stacked model to cut.

Splitting​

  • splitByFrame cuts a shape in two with the plane of a frame and gives both halves.
  • splitShapeWithShapes cuts a shape into pieces with other shapes, without removing material, as a knife would.
  • splitFaceByWires scores a face along wires that lie on it, so each region can be coloured or extruded on its own.

Section views​

  • cutByFrames cuts every shape of a list with the planes of frames and keeps what lies behind them, the side away from each normal. A cut solid stays closed, its cut faces part of it, so drawing the results shows the inside as a section view does. Each result lines up with its shape and can keep its colour; a shape cut away whole gives an empty compound.
  • With several frames, keep says what stays. behindAll, the default, keeps what lies behind every plane: six frames facing outwards keep the inside of a box, as a section box does. behindAny keeps what lies behind any plane, so only what lies in front of all of them goes: two frames cut a corner away.
  • sectionByFrames gives only the cut faces, holes included, for each shape and each frame, or with makeFaces false the section wires: the outline to hatch or dimension in a drawing.
  • The side taken away is the one a frame's normal points to, which is where hiddenLines looks from with the same frame, so one frame both cuts the model and draws the cut.
  • A design build has occt.design.section, which cuts every placed part the same way and shares the work between placements of the same part.

Where two shapes meet​

sectionWires finds the curves where two shapes meet and joins them into wires: the outline a plane cuts through a part, or the seam where a pipe meets a wall.

Drawings​

hiddenLines draws a shape as a technical drawing does, seen from a view frame and flattened: the edges the eye sees, and those hidden behind faces, which a drawing dashes. Together with sections, the result goes to DXF or SVG for a drawing or a cutter.