Describes general and AliasStudio specific concepts that you will use when modeling.
Absolute and relative addressing
Choose whether translations are made in absolute values, or relative to the object’s current placement, rotation, and size.
By default, the system addresses view coordinates in Absolute mode as indicated by the (ABS) notation as part of the move prompt on the information line. While addressing in absolute mode, an object will be moved to the grid position specified, or rotated to the absolute degree value specified for each of the three axes, or scaled based on its original size.
If you want to rotate an object on only one or two axes without affecting the rotational position on the third axis, the current values on the axis you do not want to change must be re-entered.
For example, if an object is currently rotated
to 45 degrees on both the x and y axes, and you want to change the
rotation on the x axis to 65 degrees, the rotational amounts would
be entered as 65, 45, 0 at the prompt line and then press the 
key. Trailing zero values
can be omitted, so in this case, 65, 45 followed by pressing the key would work as well.
You can switch into relative addressing mode at any time by typing a lower case letter “r” followed by the translation amounts. The notation on the information line will change to (REL) to show that the system is accepting input for relative addressing. When in relative addressing mode, objects are rotated the amount specified for each axis, relative to the object’s current rotation.
If you want to change the current rotation on only one or two of the axes without changing the current rotational position on the other axis, the values on the axis you do not want changed must be entered as zero.
For example, if an object is rotated to 45 degrees on both the x and y axes, and you want to rotate the object an additional 4 degrees on the x axis relative to its current position, the rotational amount would be input as 4, 0, 0 followed by pressing the Enter key. The zero values for the y and z axes result in no positional adjustment on these two axes.
Once again, trailing zero values can be omitted. In this case, typing 4 followed by the Enter key at the prompt line achieves the same result as well, since the relative rotational change for both the y and z axis are null.
To switch back to the absolute addressing mode at any time, enter the lower case letter “a” followed by the translation values.
Momentary and Continuous buttons
There are two types of tools in AliasStudio: momentary and continuous.
Momentary functions, such as Pick > Nothing, perform an operation once, every time you select the function.
A continuous function, like Pick > Object, remains selected and highlighted, letting you use the function repeatedly without reselecting the button. To stop a continuous function, just select another continuous function.
You can select momentary function without interrupting a continuous one. When the operation of a momentary function is finished, the system reverts to the operation of the last continuous function. For example, if you select Pick > Object and after picking a few things, want to view the scene in another window, select Layouts > Top. After the Layouts operation is performed, you will automatically continue in the Pick operation without having to re-select the Pick button.
Curvature is a measure of how much a curve curves.
Curvature is measured by fitting a circle into the curve, then taking the reciprocal of the circle’s radius. In the illustration at left, at point x, the curve is best described by a circle with radius r. At this point, the curvature is 1/r.
(We use the reciprocal, 1/r, instead of just r because a flat line has an infinite radius. Taking the reciprocal gives us 0 instead of infinity.)
Several tools in AliasStudio, such as the Locators > Curve curvature
tool, allow you to display
a comb plot of a curve’s curvature. At regular points along the
curve, the tool samples the curvature, and draws a line (sometimes
called a “quill” because it looks like a spine on the back of a
porcupine). The length of the line represents the curvature value
at that point.
Laying out curves and surfaces
As you create curves and surfaces, or fit curves and surfaces to scan data, you will have to decide how to use separate surfaces to create the overall model.
For all but the very simplest models, you will not want to create the entire model using a single surface. Sometimes the choice of boundaries between separate surfaces will be obvious. But in cases where there is no clear natural boundary, you will have to decide how to break up a large-scale areas into individual surfaces.
This is decision is a bit of an art, with different modelers making different decisions to emphasize different priorities. In this topic, we will attempt to give you a broad overview of the process.
Deciding where to separate surfaces
Consider the following cross sections:
The shape on the left has low curvature. The shape in the middle has high curvature. The shape on the right has two changes in curvature.
You will want to break up large-scale areas into areas of low curvature and high curvature at the points where the curvature begins to increase.
In areas of low curvature, not as many CVs are needed to describe the shape, so you can use a single span and a lower degree curve. Using separate surfaces for these areas lets you use simpler geometry.
In areas of high curvature, you will want more CVs to describe the shape more accurately. Using separate surfaces in these areas lets you use high degree surfaces or multiple spans to get more CVs.
Note that even if you can “get away with” describing the shape with a small number of CVs, the CVs may be doing too much work. That is, each CV is responsible for controlling such a large area of the curve or surface that making small changes to the curve or surface later will be very difficult.
You will want to break up shapes where the curvature changes direction (called inflections, shown below on the left), and where curvature begins to change (shown below on the right).
In each case, breaking the model up involves maximizing the use of CVs. That means creating conditions where no CVs are “overworked” (having too much influence on the shape of the curve or surface), and the CVs have a smooth distribution, both of which make maintaining shape and continuity easier.
Overworked (or high tension) CVs are CVs that are distant from the curve they control, or have a significant influence on the shape of their curve or surface.
In the following simplified example, the second CV in the curve on the left is clearly doing a lot of work: it’s almost solely responsible for pulling the shape of the curve to the left.
This makes editing the shape of the curve difficult. Because a single CV is largely responsible for the shape of a section of the curve (marked below), and any reshaping you want to do anywhere within section must be accomplished by moving that one CV.
This leads to extremely minute and frustrating adjustments of the CV, as you find each movement affects a larger area than just the small part of the curve you wanted to improve.
Using separate curves (as shown below on the right) immediately improves the situation. Now each CV in both curves is exerting roughly the same amount of influence.
A good distribution:
Continuity is a measure of how well two curves or surfaces “flow” into each other.
Palette tool Curves > Blend curve toolbox
.
Why you would set continuity and curve degree
Continuity is a mathematical indication of the smoothness of the flow between two curves or surfaces.
The following lists the five types of continuity possible with AliasStudio tools, G0 to G4. Note that G3 and G4 continuity are only available with blend curves.
The endpoints of the two curves meet exactly. Note that two curves that meet at any angle can still have positional continuity.
Same as positional continuity, plus the end tangents match at the common endpoint. The two curves will appear to be travelling in the same direction at the join, but they may still have very different apparent “speeds” (rate of change of the direction, also called curvature).
For example, in the illustration at left, the two curves have the same tangent (the double-arrow line) at the join (the dot). But the curve to the left of the join has a slow (low) curvature at the join, while the curve to the right of the join has a fast (high) curvature at the join.
Same as tangent continuity, plus the curvature of the two curves matches at the common endpoint. The two curves appear to have the same “speed” at the join.
Curvature with constant rate of change (G3)
Same as curvature (G2) continuity, plus the rate of change in the curvature matches between the curves.
Curvature with constant rate of change of the rate of change of the curvature (G4)
Same as G3 continuity, plus the rate of change of the rate of change of the curvature matches between the curves. This is the smoothest type of join.
The concept of “rate of change of the rate of change” may be hard to conceptualize. Consider the following graphs:
Creating and measuring curvature continuity
Additional information, hints, and tips about how AliasStudio establishes and measures curvature continuity within different tools.
Tools that use curvature continuity
Throughout AliasStudio, many surface creation tools such as Rail Surface, Square, Fillet flange, etc, attempt to maintain curvature continuity wih adjacent surfaces (if that option is chosen). Most of these tools also possess a Check continuity option that will test the level of continuity established across the boundaries after the new surface is created.
See Curvature for an explanation of curvature.
See Continuityfor a definition of curvature continuity.
In the Evaluate palette, Evaluate > Continuity > Surface continuity
is a global tool that measures
continuity across any number of surface boundaries in your model
and displays the results with color-coded locators.
Evaluate
> Check model
is another global evaluation
tool that, among other things, checks curvature (G2) continuity
between surfaces of a model for the purposes of Product Data Quality.
Curvature deviation calculation
Curvature is defined as the inverse of radius. For example, a curve with a radius of 10 at a given point will have a curvature of 0.1 at that same point. Hence, curvature increases as radius decreases.
Starting with version 13.0, all the modeling and evaluation tools use the following computation for curvature deviation:
Here R1 and R2 are the radii of curvature of the two surfaces at a matching point on their boundary.
See New Method of Curvature Continuity Evaluation for more information on this new way to compute curvature.
This calculation is carried out at several points (called checkpoints) across the boundary.
Each deviation value is compared to the Continuity
curvature tolerance given in the Tolerances:Continuity section
of Preferences > Construction Options
. If at least one of the
deviation values is larger than the tolerance, then we say that
the surfaces are not curvature continuous.
As you can see, the curvature continuity test may succeed or fail depending on the tolerance chosen, as well as number and location of the checkpoints where the calculations are done.
Curvature deviation values are dependent on one more parameter, and that is the direction in which the radius of curvature is measured. AliasStudio uses a direction perpendicular to the boundary for all curvature calculations.
AliasStudio uses two basic methods to choose the checkpoints where curvature deviation will be calculated along a boundary:
The same number of points (at evenly spaced
parameter values) are used within each span. This number is equal
to the value of the Curve Fit Checkpoints option
in the Tolerances:Fitting section
the Preferences > Construction Options window. The default is 5.
This is the method used by all surface creation tools
that maintain curvature continuity, as well as the default option
for Evaluate > Continuity > Surface continuity.
The points are equally spaced along the surface
boundary. The spacing is determined by the Distance
Between Checks option located in the Evaluate > Continuity > Surface continuity option box (and visible
when the Arc Length option is turned
on).
Evaluate
> Check model uses whatever method is
set within the Surface continuity tool.
All tools use the same curvature continuity tolerance from the Constructions options. Hence, this value has to be chosen carefully.
You may occasionally find yourself in a situation where your surface tool tells you that curvature continuity has been established across a boundary while an evaluation tool asserts the opposite.
Inconsistencies between the curvature continuity status assigned to a boundary by different tools have a variety of causes. Possibilities are:
, so the evaluation tool
views the surfaces as failing positional continuity (and hence higher
levels of continuity). This gap might have been created when the
original curves were rebuilt to create the surfaces. The tolerance
used for rebuilding curves is given by the Curve
Fit Distance in Preferences > Construction Options. Setting Curve
Fit Distance to a value smaller than Maximum
Gap Distance may remove the discrepancy.
In conclusion, if any tool warns you of a discontinuity or problem where you didn’t expect one, you should examine your geometry closely. Some continuity calculations, especially those done at the time a new surface is built, tend to be more “forgiving” than those that check the boundary after the surface has been built.
New Method of Curvature Continuity Evaluation
In AliasStudio 13.0, the way in which Curvature Continuity is evaluated was changed. This section describes the changes, the reasoning behind the changes and also explains how you can interpret the results during the modeling process.
For users of previous versions of Studio, this new method can appear significantly different from the way curvature continuity was evaluated in the past.
The intention of this section is to assure you that the change is not something that you need to worry about while evaluating the quality of your models, and to help you better interpret the results of curvature continuity evaluation at surface boundaries.
Starting with version 13.0, Studio uses a relative check for curvature continuity evaluation instead of the absolute difference check that was used in prior versions.
V13 – The Relative Curvature Deviation Method
(2)
The curvature continuity calculation has been modified for better control of surface transitions and accuracy. Specifically, the relative check was implemented in V13.0 for the following reasons:
The curvature continuity evaluation is much stricter now with the relative curvature continuity checking.
For example, in V12.0, the third curvature CV could be moved freely, yet the curvature evaluation might have stayed within tolerance. For example, as long as R1 and R2 were larger than 10 centimeters and 1/R1 – 1/R2 was less than the tolerance of 0.1, changes could be made to the third curvature CV without breaking the curvature continuity.
In contrast, in V13.0 onward, curvature continuity checking is more sensitive and flags errors more strictly.
In V12.0, the curvature deviation would change as the model was scaled. Hence, curvature continuity could be achieved within tolerance simply by scaling up the model. This can be considered acceptable as curvature discontinuity between two surfaces becomes less visibly obvious if the radius values of the surfaces become larger.
In V13.0 (and later), the curvature deviation does not change by scaling the model to make it larger or smaller – until a point is reached when a surface is scaled such that the radius is large enough to be considered flat. Flat surfaces are an important consideration now with the new curvature continuity calculation. (See Flat surfaces below).
Curvature continuity evaluation indicates a transition between surfaces and the quality of the highlight flow across surface boundaries. It is not necessary to have the same radius value on both surface boundaries for an acceptable transition and aesthetic highlight. A small difference may cause a curvature deviation value larger than 0.1 (curvature tolerance) and result in a yellow or red locator when using the Surface continuity tool, yet the quality of the highlight may be good. The curvature locator is just one factor in judging curvature continuity. You need to judge the curvature deviation value, highlights, curvature combs on cross sections etc,. and these may satisfy the desired result even with a curvature locator indicating a failure.
When Show Edge Labels is turned on (in the Surface continuity tool or Information Window), clicking with the right mouse button on the sample points of the locator shows you the radius of curvature values and the curvature deviation. The number of sample points can be increased by dragging the middle mouse button up or to the right, and decreased by dragging down or to the left.
The radius of curvature values along the boundary depend on the direction in which the curvature is measured. The direction used in Studio is perpendicular (90 degrees) to the common boundary between the surfaces.
In the Surface continuity tool, or Information Window, turn on Show Comb to display the curvature comb. The curvature comb may appear broken as shown below. This indicates that there is a change in the type of continuity failure, and is helpful when working with individual CVs.
When a relative calculation for curvature continuity deviation is used, as one radius keeps increasing, the curvature deviation tends toward the value 1.0.
This is not necessarily a visual curvature problem, but it is necessary to inform you that the radius of curvature on one of the surfaces is approaching an infinitely high value. A purely flat surface is one which has an infinite radius of curvature; therefore this condition is flagged as FLAT. A radius larger than 100000 centimeters is considered infinite. The curvature evaluation shows a yellow locator labeled FLAT only if the radius is infinite on one surface across the common boundary, and not infinite on the other one. If both radii are infinite, then the curvature deviation will tend toward zero and the curvature evaluation check will pass.
Seeing such a failure condition (as indicated by the continuity check locator’s color) does not mean that there is a noticeable curvature break. It just means that there might be a potential problem and you should use other diagnostic tools, such as highlight lines (zebra stripes), curvature combs on sections etc., to decide if the result is acceptable.
This method of indicating a flat surface in the continuity check is not unique to Studio, but is common in many other engineering or CAD software packages.
By contrast, the absolute (old) method of curvature deviation would often show that curvature continuity had been achieved in this case, even if the two surfaces had widly different curvatures at the join. To see this, substitute R1=10 and R2=1000 in formula (1). The result is 0.099, which is smaller than the default tolerance of 0.1.
Since curvature continuity is calculated differently in V13.0, its tolerance value (Continuity Curvature in the Construction Options) now has a different meaning.
In Studio, the tolerance is expressed as a number in the range of 0.0 to 1.0.
Other software packages may express the same value as a percentage. For example, a value of 0.1 in Studio corresponds to a value of 10% in other packages, and you need to be aware of this to map Studio’s values relative to that of the system under consideration.
You can set environment variable ALIAS_G2_INFINITY_TOL to any value that should be considered as an infinite radius (in centimeters).
Any radius greater than this value will be considered infinite in determining flat surfaces during curvature continuity checks. AliasStudio’ default value is 100000 centimeters.
If this value is increased, the word FLAT appears less frequently, but curvature deviation values such as 0.999 (as it’s nearing 1.0) will appear instead.
If this value is decreased, more green curvature continuity locators appear, because both surfaces have a radius greater than this value, and the curvature continuity check indicates a pass.
Using and interpreting the results
Finally, here are some important points to keep in mind while using curvature continuity evaluation during the modeling process.
The construction plane defines a temporary coordinate space that can be moved or rotated away from the absolute world space. Any reference plane can be set as the construction plane.
What is the construction plane?
Tools in AliasStudio place objects in an XYZ coordinate system. Normally this is the world space coordinate system, the absolute frame of reference for your scene.
However, there will be times when you want to align objects where the orientation, position and rotation are different from the world space axes and origin.
A construction plane lets you create and work in an alternative coordinate system. When the construction plane is active, the points you click or coordinates you type use the construction plane’s coordinate system, instead of world space.
You create a construction plane by using the Construction > Plane
tool.
You can position and rotate the construction plane freely, or constrain it in relation to a curve or surface.
You can switch between world space and an active
construction plane by choosing Construction > Toggle Construction Plane
.
What is the relationship between construction planes and reference planes?
You can have many reference planes in your scene performing various jobs, but only one plane at a time can be the construction plane.
You can tell AliasStudio to use any reference
plane as the construction plane by choosing Construction > Set Construction Plane
.
AliasStudio has two tools for dynamic shape modeling: a Lattice Rig tool and a Transformer Rig tool.
Providing two separate tools gives you the following benefits:
For information about these toolboxes and tools,
see Object Edit > Dynamic
Shape Modeling > Transformer Rig
and Object Edit > Dynamic
Shape Modeling > Lattice Rig
.
Why we developed dynamic shape modeling
The Dynamic Shape Modeling tool family was developed to support global modification of datasets. While it is relatively straightforward to modify just one piece of geometry, it can be a very time-consuming task to change the proportions of an entire model composed of many pieces of geometry. As a designer, you need to explore the proportions of the model. To play with it, you need to be able to modify the whole set of geometry, sometimes as a single unit. The result doesn't need to be a production model, just a model that holds together, expresses the intent of your design, and enables you to make a choice before you finalize your design.
The purpose of dynamic shape modeling
The Dynamic Shape Modeling tools give you the ability to globally change the model easily. Think of it as an advanced non-proportional modification tool that stretches and compresses the model. The basic relationships of parts of your model to each other will not change, and features can not be added or subtracted, but within the model, relative sizes, proportions, and shapes can be modified.
What Dynamic Shape Modeling doesn't do
There is no guarantee that surface continuities are maintained while the global shape is being modified. After the shape modification, you'll need to check the model, and perform additional work to fix the continuty breaks, as necessary.
Using Dynamic Shape Modeling for communication and concept development
Using Dynamic Shape Modeling for further modeling and modification
Common concepts of Dynamic Shape Modeling
While the tool sets have significant differences, they share the following concepts.
A target is any geometry that is being modified.
Targets can be surfaces, meshes, or curves.
A modifier is geometry used to define the desired changes to the targets.
Constraints are used to secure parts of the target geometry to prevent shape modifications.
What happens with the target geometry?
As soon as the targets are picked and accepted, the tools duplicate the targets. Shape modifications will happen on the duplicated model. The original geometry is made invisible.
While you are modifying the shape of the geometry, the dynamic shape modeling tools allow you to toggle the visibility of the originals and the modified geometry. This makes it easier to compare your modifications with the original.
If, for any reason, the duplicated geometry (visible geometry with dynamic shape history) is modified in such a way that the construction history has to be deleted, the original geometry will be set visible and made into a template.
The tools allow you to revert a modifiction by deleting the duplicated geometry and restoring the original, or commit to a modification by deleting the original and the history.
The Lattice Rig tool uses a lattice to effect global shape modification. The geometry is shaped by moving the lattice points, which squeeze and pull the model.
The geometry that can be globally modified is called a target. Targets can be surfaces, meshes, or curves.
A manipulator used to articulate the desired changes to the targets.
A proxy is a lightweight wireframe representation of the targets being deformed by an engaged lattice. The proxy interactively updates while you modify the engaged lattice to show what the targets look like after deformation. Meanwhile, the targets remain unchanged until you release the mouse button (when auto-recalc option is ON) or when you click GO (when auto-recalc is OFF).
The lattice is a manipulator in the Lattice Rig tool. It is initialized as a bounding box around the target geometry.
The lattice has two modes: disengaged and engaged. A disengaged lattice is drawn with dashed lines, and when modified, has no influence on the target geometry. This gives you the ability to refine the lattice to suit the intended modifications of the target geometry.
An engaged lattice is drawn with solid lines, and when manipulated, will modify the target’s geometry.
You can shape the disengaged lattice so that it does not fully enclose the targets.
When the lattice is engaged, everything that is outside the lattice will remain unchanged; everything that is inside the lattice will be modified.
To facilitate this, parts of the lattice that intersect the targets are locked and drawn in red.
In disengaged mode, the lattice points are modifiable; in engaged mode these points are not modifiable.
What is the lattice rig used for?
The Lattice Rig tool is especially suited to general volumetric shape changes to a model. Consider using the Lattice Rig for more conceptual and fast explorations.
The geometry that can be globally modified is called a target. Targets can be surfaces, meshes, or curves.
Modifiers are geometry used to articulate the desired changes to the targets. In the Transformer Rig toolbox, these are Modifiers.
To secure parts of the target geometry to prevent shape modifications, use constraints. Dynamic shape modeling analyzes the transformer rig and assumes the constraints delimit a region of interest (ROI). Parts of the targets that lie outside of the ROI will be clamped (they will not move). The estimate of the region of interest, however, is not always correct. If there are inaccuracies in the ROI, use clampers.
Clampers are hints you place outside the intended region of interest to help the tool understand the desired ROI. Clampers help ensure that modifications don't happen outside the ROI.
In some cases, there are geometries or objects within the target geometry that should keep their shape. Usually these are parts like buttons, door handles and lights. These rigid targets will be moved embedded in the flexible targets, but they will not lose their shape during the warp. Making a target rigid helps preserve the shapes of the parts while allowing them to move with the surface. Imagine grommets moving on a rubber tarp that is stretched to cover a load: the grommets remain the same shape and size on the flexible surface of the tarp.
What is the Transformer Rig used for?
The Transformer Rig tool is used for more controlled shape modifications driven by specific features of the model.
Custom modifiers and constraints:
The Transformer Rig enables you to create custom modifiers specific to the model being changed. This provides tighter control of the surface modification.
The Transformer Rig also enables you to constrain parts of the selected target geometry. You can select real geometry to constrain the modifications, which makes the entire warp result more precise, and enables you to make finer-grained changes.
The Transformer Rig offers more flexibility with NURBS fitting options
The Transformer Rig offers an additional NURBS fitting method called Adaptive.
Add a clamp to surfaces in Transformer Rigs
Use predefined modifiers with Transformer Rigs
Use rigid targets with Transformer Rigs
