8e. Knife Types

When you click on the Knife tool a pop-up window will appear allowing you to select one of three knife types. This window will remain in view until some other tool is selected. To use all knife types, click and drag to draw a straight or diagonal line in any view window. The specified knife action will take place when you release the mouse button.


The first knife type (destructive type) will add a point to every curve at the intersection of the knife line and the curve. The newly added points will not be connected, thereby destroying any patch/face through which the knife line cuts.

The second knife type (conservative type) will add a point to every curve at the intersection of the knife line and the curve. Only the newly added points which pass through a currently existing face will be connected, thereby preserving any patch/face through which the knife line cuts.

The third knife type (constructive type) will add a point to every curve at the intersection of the knife line and the curve. All newly added points will be connected, thereby preserving old patches/faces and constructing new patches/faces whenever a set of 3 or 4 connected points exists. However, the constructive knife will not close a spline, it will only add curves until all points have been dealt with at least once.

Example: If you inserted a cylinder then used the destructive knife to cut through the center in a front view, you would be left with two floating discs. Or if you used the conservative knife all patches would be preserved and you would not see a difference. If you used the constructive knife the two floating discs would reappear, but this time they would be connected by an S-shaped patch. The constructive knife connects newly added points in the order that they were cut into the object, so cutting from left to right: the left most point is connected to the back point, then it curves forward to be connected to the forward most point then it curves a final time to connect to the right most point. Varying the method of cutting and the view angle, you might be able to simulate the same results as the conservative knife using the constructive knife on the cylinder.

If there is some other feature of hamaPatch that you need further explanation on or for questions, comments, or additions to this documentation please contact: draven2561@hotmail.com.
Documentation by Jonathan Lee Jan. 18, 2005.

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