Thursday, October 22, 2009

Parametric modeling - Part 2

Geometric Constraints

The first panel on the left side of the Parametric tab is for the tools that create and modify geometric constraints. These are the relationships that are applied between two objects, points on objects, or between a single object and the coordinate system. In simple terms it works like an object snap that stays persistent throughout your design.

The middle sub panel on the Geometric constraints panel contains the commands that you will use to apply the constraints to objects in your drawings. These can be accessed from this location on the ribbon or with the GEOMCONSTRAINT command. There are twelve to choose from, we’ll cover each of them.

Coincident - Constrains two points on two objects together. A constraint point on an object can be made coincident with an object or a constraint point on another object. When the cursor hovers over the constrained point, the constraint bar to the right is shown.

Colinear – Constrains two or more line segments to lie along the same line. Regardless of how the original line is moved or rotated, the Colinear line will move to match the new location.

Concentric - Constrains two circles to the same center point. This also works for arcs and ellipses. The result is the same as that of a coincident constraint applied to the center points of the curves. Moving one of the circles will move the other with it, much like a block.

Fix - Locks a point or curve in position. The fixed point can be on an object, or a point in relation to an object, like a center point of a circle for example. This command may be a let down for those people who thought it might fix something in the drawings that doesn’t seem to work the way they wanted it to.

Parallel – Constrains two lines or polylines to be Parallel to each other. When one is modified the other will move to match it.

Perpendicular - Causes selected lines to lie 90 degrees to one another. Perpendicular constraints are applied between two objects and, unlike the Perpendicular object snap, these lines do not have to be touching each other when the constraint is created.

Horizontal - Causes lines or pairs of points to lie parallel to the X axis of the current coordinate system. Be aware when using this constraint that they are set to the axis in the coordinate system in which they were created. When another user coordinate system is active the Constraint bar icon (pictured below) will change to show that the current axis in not the one that the constraint was created in.

Vertical - Causes lines or pairs of points to lie parallel to the Y axis of the current coordinate system. Just like the Horizontal constrain these are set to the axis in the coordinate system in which they were created. When another user coordinate system is active the Constraint bar icon (pictured on the right) will change to show that the current axis in not the one that the constraint was created in.

Tangent - Constrains two objects to maintain a point of tangency to each other or their extensions. Tangent constraints are applied between two objects, those objects could be a curve (arc or circle) and a line or another curve.

A circle can be made tangent to a line even if the circle does not touch the line and a curve can be tangent to another even if they do not physically share a point.

Smooth (G2) - Constrains a Spline to be contiguous and maintain continuity with another spline, line, arc, or polyline. When the constraint is applied the endpoints of the curves to which you apply the smooth constraints are made coincident.

When two Splines are selected, they are updated to be contiguous with one another. This function is similar to using the JOIN command for polylines except the splines are not joined to be one object; they only behave as if they were one object.

Symmetric - Causes selected objects to become symmetrically constrained about a selected line. The function is similar to that of the Mirror command. Unlike other constraints where two objects are selected, with a symmetric constraint you must have an axis around which you will constrain the objects or points to be symmetrical.

This is referred to as the symmetry line. For lines, the line’s angle is made symmetric and not the endpoints. For arcs and circles, the center and radius are made symmetric not the endpoints of the arc.

Equal - Resizes selected arcs and circles to the same radius, or selected lines to the same length.

Monday, October 19, 2009

Parametric modeling

Parametric modeling

The biggest and initially the most intimidating new feature in AutoCAD 2010 is Parametric Modeling. You may be surprised to find that there is no actual Parametric command. That’s because it’s the name for a new set of tools that allow you to create geometric relationships between objects or restrict the dimensional properties of objects. The two different types of tools are referred to as geometric and dimensional constraints. That doesn’t sound that complicated now does it?

Well before you panic and pull out the old dictionary that you used to use to decipher what Dennis Miller said on Monday night football, relax. We’ll go through the tools and their usage in plain English and before you know it, you’ll see that it’s really not complicated at all.

All of the constraint settings and display options are handled by the Constraint settings dialog box. You can open it with the CONSTRAINTSETTINGS command. We’ll refer back to this command as we cover the different constraint functions and commands.

Another important feature that is used with the constraints are the Constraint Bars, these show which constraints are applied to drawing objects. The CONSTRAINTBAR command effects how the constraint bars are displayed. When constraint bars are displayed, you can pass the cursor over a constraint to view the constraint name and the objects that it affects. You can also control the display of constraint bars with this command or use the Show, Show All, and Hide All options on the Geometric panel of the Parametric ribbon tab.

There is a new Tab on the menu ribbon for the parametric modeling tools called the Parametric tab. This tab is broken down into three panels, each with a different set of tools that you would use for the different constraint functions. Over the next few posts we'll look at each separately.