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Selection, manipulation and editing of entities

Short answer

Selection methods include picking, window, crossing window, fence/lasso, multiple-select, filters and grips. Manipulation commands are move, rotate, scale, mirror, copy, pattern and stretch; editing commands include trim, extend, break, join, offset, fillet, chamfer, delete, modify and suppress. These tools prevent errors and speed up modelling.

Write short notes on the selection methods and the manipulation and editing commands used to modify entities in a CAD system.

Before an entity (line, arc, face, feature, part) can be edited, it must be selected. After selection, commands manipulate it.

Selection methods

  • Pick (click): direct selection of one entity, using a pick box (aperture) around the cursor.
  • Window: a rectangle drawn from left to right selects entities completely inside it.
  • Crossing window: a rectangle drawn from right to left selects entities inside or touching it.
  • Fence / lasso: a line or free-hand shape selects whatever it crosses or encloses.
  • Multiple (Ctrl/Shift) and select-all: add or remove entities from a set.
  • Filter / by property: select by layer, colour, type, name or feature.
  • Drag: hold and move an entity or handle (grip) to change position or size.
  • Previous / last: reuse the last selection.

Manipulation (transformation) commands

  • Translate / move, rotate, scale, mirror (reflect), copy, pattern (linear, circular), stretch.
  • These use homogeneous transformation matrices (3×33\times3 in 2D, 4×44\times4 in 3D); for example, a 2D scaling by Sx,SyS_x, S_y about the origin gives x′=Sxx, y′=Syyx'=S_xx,\ y'=S_yy.

Editing commands

  • Trim / extend a curve to a boundary, break, join, offset, fillet, chamfer, explode (split a group).
  • Delete, undo/redo, modify a dimension, edit sketch, suppress or roll back a feature.
  • Grip editing: move control points of a curve or surface to change its shape.

Good selection tools reduce errors and speed up modelling: working with layers, groups and filters avoids selecting the wrong entity.

✓ Answer checked by Claude Opus 5.5 (high effort)

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