From FreeCAD Documentation
- Double click Sketch002 to enter edit mode.
- Rotate the view so you can clearly see the points as shown in Fig: CC2. This will ease subsequent steps. Note that the rectangle's initial position may be different in your sketch.
- Click External geometry.
- While the tool is active the cursor has this appearance:
- Select point P1 in Fig: CC2. The selected point is added to the sketch as external geometry. In the Elements section of the task panel it will appear with a purple X icon or, introduced in version 0.21, a purple dot icon.
- With the tool still active select point P2 in Fig: CC2. This external geometry should also appear in the Elements section.
- Exit the tool.
- Select point P1 and point P3 and apply a Vertical constraint. The rectangle will be aligned with the X position of P1.
- Select point P2 and point P3 and apply a Horizontal constraint. The rectangle will be aligned with the Y position of P2.
- You should have a fully constrained sketch similar to Fig: CC3.