After quite a long period of silence, here's a new episode to add in the sPatch tutorial serie. It's a very short one but it's emphasizes an important point of modeling with sPatch. I needed a suitable object to make my point so I chose swords and blades in general. Swords are fairly common objects in raytraced imagery but they quite often lack in quality, so why not kill two birds with one stone. I still haven't explained what this important sPatch technique is ... don't worry I will in due time!

a simple sharp profile 

Use add tool  to draw a simple blade profile in the XY plan. Weld the end points in order to obtain a closed loop. To make the blade sharp, use the peak tool  on your profile. Note: for the purpose of this tutorial I chose a very simple double sided blade profile. But you can draw a more complex one. It is especially interesting to add segments in the central body of the blade. This will allow you to create grooves and bumps on the blade body. The rendered sword used in the title was created that way with a central groove running along the blade.

create the blade

Extrude  the profile twice along the Z axis. The first extrude should be long and generates the blade, the second one shorter will be used to create a seamless curvy tip.

create the tip of the sword

Pick  all the points of your last extruded profile except the two forming the cutting edges. Translate  this selection back along Z untill it stand roughly half way in the last extrude. Now use the scale tool  with only the Y axis active. Scale down the selection untill selected points on each side overlap (when this happen you should not be able do scale it back up! ... unless using Undo). Release that selection (press Enter) and pick  the last two point of the end profile. Scale  it down the same way to close the tip of the blade. You just created a really neat sword blade without any problems :-) Thanks to sPatch!

now making my point!

Modeling that blade was actually so simple that you think it does not deserve a tutorial. Well it does! I can prove it. Select  your entire blade and use the round tool on it. What do you get? A very unrealistly blunt sword (top left) ... it does NOT look good.  Now if you peak  the tip point it doesn't solve the cutting edges problems (top right). It's all right you think, I can also sharpen these by using the peak tool . Well, no because you then loose the curvy transition between the blade and the tip (bottom left and right). Argh, the only way to get the original shape back is to use peak tool  on individual edges rather than on points. The trick is that when applying the peak  and round  tools on a selection of points these act on both direction at the same time (u and v for the spline aware people). So to get the smooth transition back you must select the edge you want to be smooth (pick a point then hit TAB until the desired edge is highlighted) and round it. ... quite tedious as each edge might need two click + several TABs to be rounded!

conclusion: ALWAYS extrude along the curve you need!

The moral of this tutorial is this one. When modeling an object you want sharp  in one direction and round  in the other you should always proceed as for this sword. Draw the sharp profile, and extrude it to obtain a curve. This is the most efficient way to obtain the shape you desire. Trying to extrude the smooth profile along a sharp path will lead to painfull cession of TABing to smooth individual edges.

This is summarized in The sharp/curvy mini tutorial.