This is actually a double tutorial...the intent is to show how to use Rhino to "digitize" plans that you may have scanned in or downloaded off the internet. The other goal of the tutorial is to show how to use Rhino to generate quality curves with smooth transitions and blends.
Scanned files and downloaded files are usually in "raster" format...this basically means that they are either a .tif, a .jpg, or a .bmp. There is a whole class of software that supposedly outputs a nice vector file (i.e. a CAD file) if you give it a raster image, but I have yet to see one that works as well as the method I'm showing below.
For this example, I did some googling and located an image on the web to work from.
Step 1: Insert the image into the background\
Click View>Background Image> Place
This will allow you to select an image file and then position and scale it in the drawing area (see the result below)
Step 2: Scale the image to match the instrument
You can do this by either using the "Align" option or by using the "Scale" option in the View>Background Image menu:
I pick a feature of a known length to scale everything off of. In this case, I referenced the distance from the nut to the 12th fret. I drew a line of the correct distance and then used the options mentioned above to scale the image correctly (I recommend using the "Align" option).
Step 3: Adding Construction Geometry
I drew in a line that goes from the neck joint to the butt of the guitar, and I also added a vertical line at each end. For ease of viewing, I usually draw in color when I'm sketching on top of a black and white plan.
Step 4: Draw the rough contour
I use the command "Curve Interpolate Points" to sketch in a spline. The trick with this part of the process is to use as few node points as possible. Using the minimum number of nodes makes it easier to clean the curves up.
[img]Step%205:%20Placing%20Nodes[/img]
The image below shows an appropriate number of nodes; my general rule of thumb is to put a node on there every time I span 45 degrees. It is important to make both ends of the spline connect directly to the endpoints of the centerline (where the 2 vertical lines branch off). Rhino has Object Snaps that make this as easy as pointing and clicking.
Step 6: Cleaning up the Curves
The next step is to clean up the curve manually. I use the "control points on" option to show the control points for the spline. Once these points are displayed (the points in interest are the ones connected by the dashed lines). You just click on any of these points and pull them around to make the curve conform more closely to the image.
Step 7: Adjusting Tangency
Now, this is where it gets good: We'll use the match curve command to make the spline tangent to the vertical at each end. You click the button shown, then click on the curve you want to change and the curve you want to match. It's a great idea to do some doodling and to play around with all the options within this command.
Step 8: Checking for Smoothness
To give everything the once over, we'll use the Curvature Graph. This is a tool that will help you iron out any little dips that might be in the curves. I'm sure we've all made something that looked decent...only to run your finger over it and to be able to feel where the curves just don't transition quite right. If you get used to this little tool...those days will be numbered!
Step 9: Why Less is More!
Now, remember where I said not to use too many node points? Here's a good example of what your curves may look like if you use too many. You generally want to see nice smooth transitions...it's OK if some of them kind of "knee" over a bit...but if you see spikiness those curves are probably not something that will be right in the end.
Step 10: Mirror the profile
At the end of it all, you just mirror the one half about the center line and you have a completed profile with nice smooth curves. Since we set the ends of the profile tangent to those vertical lines, that guarantees that there will be a smooth transition from the bass side to the treble side.
A lot of these same techniques and ideas are used in making 3D models as well. Learning how to use them for 2D drawings is the first step in getting there.
I hope this helps get you started - please drop me a line if you have any questions!
Best,
Trev