CAMERA PROJECTION

 
Using the drawing pen draw a shape overlapping with an object.
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Press K. If you have not turned off the "Confirm Actions" press OK or ENTER.

Expand the menu from the bottom left corner of the screen. Select "UNION" boolean option .

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If you are in default mode your lines might be burried inside the main object. If you wanted them to be on the surface of the object select "Camera Projection".
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Switch to perspective view by pressing "0" on numeric pad to see the shape from a different angle. You will see that your lines are projected to the surface of your object.
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Back in camera view ("Cam_Carve"), adjust to a new angle and draw a mew shape.
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If you switch to the perspective view by pressing "0" on the numeric pad you will be able to see the relation between the object's extrusion and the carving camera. If the "Extrude To Camera" button is on you will see that the shape is extruded along the camera axis towards the camera("Cam_Carve").
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Increase the "Extrusion Depth". Notice how the shape points at the carve camera ("Cam_Carve").

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Press "0" again to switch back to Camera View. Draw a new shape from a different angle.
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Switch to "DIFFERENCE" mode for an inset volume.
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Draw another shape from another angle.
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Select "Lines_Only" check box while still in "DIFFERENCE" mode. Notice that the lines lie on the surface of the main object as they carve a "canyon" of sorts.
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Draw another shape.
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Switch to "UNION" mode. The new lines are now protruding but still on the surface.
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