Rhino L1 05: Intro to Snapping

Summary:

Today I’ll introduce you to precision modeling in rhino utilizing geometry snapping “OSNAP”, as well as the importance of tolerances.

Full Video Transcript:

Today we’ll be focusing on precision in Rhino, and if you’re used to CG graphics apps like Maya or Modo, Rhino’s precision modeling tools are going to blow your mind.

The best way to learn about Rhino’s precision tools will be to start with 2D geometry, and then translate that knowledge into 3D in a later class. Move to the Top view, and activate the rectangle tool. We know that we can create a measured rectangle by enabling the “Snap” toggle at the bottom, which activates grid snapping. Click a major grid square to define a start point, and ten grid squares away to define an end-point.

We also know that we can define the exact size of an element by typing values in the command line. Right-click to reactivate the rectangle tool, click the bottom-right of the first rectangle to begin, then type the dimensions. There’s no need to click the command line first, just start typing, and Rhino will know what you want to do. Type 10/1.618, right-click, and to repeat the same dimension on the Y by right-clicking again.

The grid is great, but it will only get us so far. If we want to model anything even moderately complex in Rhino, we’re going to need to be able to snap to geometry. This is where Osnap comes in. Click the Osnap button at the bottom of the screen to display the various geometry snapping options.

Here’s where I need to warn you: hear yee, hear yee, Rhino beginners. When working with Osnaps in Rhino, always enable the “Project” option. We won’t explain what it does just yet, but just be aware: if you’re using Osnap and strange things start happening to your model and 3D objects are jumping all over the place whenever you snap to something, chances are the Project option isn’t enabled. Just leave it on until I tell you otherwise. SmartTrack should be on by default, but if it isn’t, go ahead and enable it.

Clicking Osnap doesn’t actually enable any snaps, it just gives you a handy list of the options. Let’s walk through them one by one.

Click the check box to enable the End point snap, activate the Polyline tool, and when you mouse over the top-left corner of the first box, notice that the word “end” appears, telling you what Rhino is snapping to. When you click to define the second point at the lower-left of the second rectangle, the same indicator should pop up. This might seem obvious now, but with more complex models, you’ll really appreciate this feature.

Reactivate the Polyline tool, and click the lower-left of the big square, then hover over the upper-right of the smaller square, but don’t click. I know that this is the direction I want the line to go, but I don’t know how far exactly just yet. Hit the [tab] key, and Rhino will lock the current direction vector for the line, but await another command to define the length. Mouse-over the top-right of the small box until a little white dot appears, telling us that SmartTrack has kicked-in, and then move the mouse up to the theoretical intersection between the right-edge of the small rectangle and the current trajectory of our line. SmartTrack has inferred that we want to snap to the point directly above the white point, and it’s correct! But notice that it has also recognized an implicit intersection, and the word “Int” is visible in the white box this time. Click to finish the line.

Since we’ve got that “Int” snap on the brain, let’s enable that one next. When we mouse-over the intersection between a diagonal and a box edge, we can see that little white “int” appear again, and then we can click another ‘end’ snap to finish the box. You can enable as many simultaneous geometry snaps as you like, but they can get cumbersome if you leave them all on at once.

Use the End and Int snaps to define a few more boxes in the series.

We can keep going, and going.

And going. And going.

In fact, we could take this all the way in until the absolute tolerance of the document wouldn’t let us go any further, but that’s a long, long, long way. The point of this exercise is to show that Rhino’s snapping tools allow us to be as precise as we want to be. In my case, plus or minus .001mm, or one micron. To give you a sense of scale, a human hair is around 50 microns in diameter, so plus or minus 1 micron is? precise.

Next we’ll try the Mid snap, which is pretty much what it sounds like: it lets us snap to the midpoints of lines. Draw another square, and then draw a diagonal. Use the Mid snap to create a right triangle in one half of the square, and then another within that, and another within that. You get the point.

Next we’ll try the Center snap, but this time make sure to disable grid snap. Draw a circle in an arbitrary location, and then activate the ellipse tool. Since we can’t use grid snap to find the center of the circle, we’ll use Center snap. Mouse-over the edge of the circle and the ‘Cen’ flag tells us that we’ve snapped to the center of the circle. Move the mouse to the right, and since we want the ellipse to be perfectly horizontal, hold the ‘shift’ key to temporarily enable Ortho snapping. Move to the edge of the circle, and the ‘Int’ snap lets us snap the edge of the ellipse to the edge of the circle. Click to define an arbitrary height.

Activate the Circle > Circle by Diameter tool, to enable the Quad snap and disable all other snaps, just right-click the check box. Quad lets us snap to the top, bottom, right, and left of circles or ellipses. Move near the top-center of the ellipse, and the Quad snap will kick in. Use the same to define the bottom of the circle.

Draw another arbitrary circle, then enable the ‘Near’ snap. Near lets us snap to any arbitrary point along a curve. Use the polyline tool to draw an arbitrary triangle within the circle. Enable the Mid and Perp snaps, and activate the polyline tool. Draw perpendicular lines from the mid-points of each side of the triangle to find the center of the circle.

Use the point tool to draw four arbitrary points. Activate ‘Point’ snap, and then use the Control Point Curve to draw a curve by snapping to each point. Enable the Tangent snap, run the Polyline tool, and use it to extend the spline tangents at either end.

Finally, select the spline, and click “Edit Points On” in the Main toolbox. Enable Knot snapping, and activate the Polyline tool. Click any knot along the spline and pull out a line perpendicular to it. Type ’1′ and hit enter to define the length. Do this for each knot along the spline, then activate the Curve > Curve Interpolate Points tool. Click the end points of the ribs to create a perfect offset of the first curve.

I should point out that this would be a ridiculously labor-intensive way of offsetting curves in general; I was just using it as a demonstration. To offset a cuve a given distance, just use Curve Tools > Offset Curve, select a curve to offset, type ’1′ enter, and click to commit.

One more tool for the day: use the Control Point Curve to draw an arbitrary shape. In perspective view, run Surface > Revolve. Select the curve, right-click, click twice to define a center line, hit ‘enter,’ type 360, hit ‘enter,’ and shade the viewport.

Sweet. Have fun. These better be some sweet space stations by now!

[/j_protect]

about adam: Adam O'Hern is an industrial design consultant specializing in visual brand languages, and has designed products ranging from laptops to power tools, classroom toys to bathroom fixtures, and robots to lint rollers. He has published with 3DWorld Magazine, CGTuts+, and Luxology, and works with Josh Mings of SolidSmack.com on EngineerVsDesigner.com.