Dimensioning
Change the dimensions of existing geometry, thus changing the basic shape of solids and other enclosed volumes.
Edit Dimensions
Dimensioning is accomplished with features, parameters and dimension manipulators.
When changing several dimensions, each dimension change is performed separately using the respective manipulator. However, if multiple dimensions are linked to the same parameter or parameter expression, they will be updated simultaneously.
When dimensions are modified, a very limited check for mutual penetrations of the repositioned surfaces is performed. It is the your responsibility to ensure that the new dimensions are appropriate.
The locked end of the dimension manipulator defines the direction in which the affected surfaces move when the dimension is modified. For a dimension to be modified, one or both ends of the dimension manipulator must unlocked.
When dimensions cannot be modified, the locked side is set to Both and you may use the Sides Selection advanced option to specify how the dimension should be changed, when possible.
Dimensioning Concepts
Learn about basic dimensioning concepts, such as continuous surface offset functionality and tolerance and accuracy.
Continuous Surface Offset Functionality
Dimensioning is based on a continuous surface offset functionality. It provides assistance in the selection of the surfaces to offset so that a change to the selected dimension can occur, and calculates the offset values required for each surface to achieve the specified dimension.
The continuous offset modifies both the surfaces you selected for the offset and the adjacent involved surfaces that must also be modified so that the result will remain as continuous as the initial input.
- Selected surfaces
- Offset by a constant value that is normal, or in some cases almost normal, to the surface at each point. For example, a standalone surface is offset by the given constant distance exactly normal to itself.
- When the adjacent surfaces form a corner between them, the exact normal offset will result in either disconnected surfaces or in intersecting surfaces, for example if the offset was performed in the opposite direction.
- A continuous result that is consistent with the given offset distance is obtained by reconciling the offset vectors of the vertices shared by the surfaces being offset.
- Involved Surfaces
- The edges of the involved surfaces that are shared with the selected surfaces move with the selected surfaces.
- The edges of the involved surfaces that do not have a common point with the selected surfaces do not move, for example they are locked.
- The offset of the edges that connect both the moving and the locked involved surface edges is defined by interpolation. Different interpolation methods are available.
- If both dimension ends (both vertices) are allowed to move, an attempt is made to move them by the same distance whenever possible.
- If possible, the dimension ends are moved in such a way that the direction of the dimension will not change.
Tolerances and Accuracy
All geometry transformation tools are numerical tools that operate with some accuracy defined by the tolerances, such as the geometry cleanup tolerance set in the Options panel. Curved surfaces and lines have internal structures in 3D that are invisible to you. Significantly reducing the size of such an entity so that these structures fall below the tolerances may result in a structure simplification that you cannot notice at first; the structural data will be lost. When this occurs any subsequent increase in the size will not restore the initial structures. For example, reducing a cylinder diameter 100 times and then increasing the diameter 100 times may not lead to the same cylinder; in some cases, a complex internal representation of the cylinder may lead to a corrupt surface. In general, transformation of a curved entity may result in both the simplification or complication of its internal structure. It is therefore not recommended to perform multiple transformations on curved entities.
Dimension Manipulators
Dimension manipulators are used to alter selected dimensions of solid entities.
- Dimension line
- A segment parallel to the line that connects the selected points, but is shifted off the selected points for visibility. The terms manipulator direction and manipulator ends are also used, which are the same as the dimension line direction and the dimension line ends.
- Pullout lines
- Two parallel segments that connect the ends of the dimension line with the selected points.
- Lock icons
- Arrow (movable) and block (locked) icons indicate the lock state of a manipulator end.
- Lock controls
- Sphere handles, located near the lock icons, enable the lock state of a manipulator end to be modified.
- Display/input field
- Displays the current dimension value, which can be modified or deleted. This value can be modified or deleted. Deleting the value deletes the the manipulator. For dimensions that are parameterized, an "&" symbol will appear before the dimension. Editing a parameterized dimension directly edits the parameter, or parameter expression.
Dimension Feature Attributes
Attributes associated with dimension features can be modifed in the Entity Editor.
Attribute | Action | ||
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Lock Side | Select the locked end of the dimension manipulator, which defines
the direction in which the affected surfaces move when the dimension
is modified. For a dimension to be modified, one or both ends of the
dimension manipulator must unlocked. When dimensions cannot be modified, the locked side is set to Both and you may use the Sides Selection advanced option to specify how the dimension should be changed, when possible. |
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Surfaces Interpolation System |
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Minimum Slide Angle | When a selected surface is offset, the involved surfaces must be
modified to keep the continuity of the model. Surfaces can be modified by dragging the involved surface behind the selected surface, or by defining it as a "slider" along which the selected surface slides. The Minimum Slide angle determines which method is used. If the slide angle is more than the specified value, then the involved surface will slide; otherwise it will drag. When the involved surface is a
slider, the orientation of the surface does not change for
planar surfaces. However, for curved involved surfaces, the
sliding directions are defined by the tangents to the surface
where it is adjacent to the selected surface. Sliding of the
selected and involved surfaces along these directions may also
result in some change to the shape of the involved surface.
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Remove Collapsed Surfaces | Remove portions of the offset surfaces that fold into themselves
or adjacent surfaces (portions of surfaces that penetrate themselves
or adjacent surfaces along the edges they are adjacent over). For
example, suppose that the slide angle is greater than the
Minimum Slide Angle and the value in the dimension manipulator
is set to 1. If this option is off, the involved surface will
slide and ignore the self-penetration, resulting in a corrupt
model. If this option is on, the involved surface will slide as
far as possible without causing self-penetration. This may not
allow the specified dimension to be reached, but will not result
in a corrupt model.
In general, unless it is known that collapsed surfaces will result, it is better to keep this option off for performance reasons, as this option has no effect on general cases that do not result in penetration. |
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Sides Selection |
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Advanced Considerations
Advanced considerations to keep in mind when changing the dimensions of existing geometry.
In practice, changing of a linear dimension in a model normally implies either stretching/compressing in the direction of the modified dimension or changing of a diameter/radius. With dimensioning funtionality, a combination of both modification types is provided.
When the value of the upper dimension manipulator is modified from 52 to 60, the edge fillet surfaces are adjacent to the modified manipulator and are offset as selected surfaces. As such, they are offset with the LSC interpolation, which results in a preservation of their shape along with the change in radii.
When the value of the lower dimension manipulator is modified from 52 to 60, the edge fillet surfaces are not adjacent to the modified dimension manipulator and are curved, so they are offset as involved surfaces. Using automatic interpolation, it is recognized that these two curved surfaces can be simply stretched to provide the model continuity via the global interpolation method.
- The required shift in the dimension manipulator direction is calculated as a difference between the requested distance and the actual distance between the dimension manipulator ends.
- If both dimension manipulators ends are allowed to move, the required shift is
divided by two.
When Sides Selection is set to Auto, an end is allowed to move if it belongs to a surface that is automatically selected to move. When this can be overridden manually by you, the lock controls appear.
When Sides Selection is set to Manual, an end is allowed to move if it belongs to a manually selected surface, and the surface normal at the dimension manipulator end forms an angle with the dimension manipulator direction that is less than arccos(0.05) (87.134016 degrees).
For example, the right end of the dimension manipulator belongs to only the selected surface 2. The normal to surface 2 at the right end creates a 90-degree angle with the dimension manipulator and thus the end is not allowed to move. The left dimension manipulator end belongs to both selected surfaces 1 and 2. The normal to surface 1 at the left end makes a 0-degree angle with the dimension manipulator direction, and thus the left end is allowed to move. - When only planar surfaces are selected, the absolute value of its normal offset
is defined as the absolute value of the required shift multiplied by the cosine
between the normal to the surface and the dimension manipulator direction.
For a planar surface, this provides that its shift in the dimension manipulator direction is equal to the required shift.
When curved surfaces are included and the Sides Selection is set to Manual, the rules of the offset value calculations are more complex. The problem in this case originates from the fact that a selected curved surface can provide a smooth link between the selected planar surfaces that are tilted by different angles versus the dimension manipulator direction. When smooth, adjacent surfaces are offset, they must be offset by the same value to ensure continuity of the result, because in this case it is not possible to reconcile the different offset values as discussed earlier. This means that the planar surfaces with a different tilt towards the dimension manipulator direction cannot be offset by different distances, as shown above, when the planar surfaces are smoothly linked by a selected surface.
The current algorithm to define the offset value in the general case, for both curved and planar surfaces, is as follows. For a selected surface adjacent to the dimension manipulator end, its offset is calculated as shown in the image above, based on the normal to the surface at the dimension manipulator end. For a selected surface that is not adjacent to the dimension manipulator end, a chain of selected surfaces that links it to the related end is detected, and the offset is calculated along the chain, from the previous surface to the next. The calculation along the chain is based on the following:- If the surfaces are smoothly adjacent, the offset value is directly passed from one surface to the next.
- If the surfaces are not smoothly adjacent, the offset is calculated in such a way that for a planar surface the result as shown in the image above is obtained.
The problem here is that when several chains of selected surfaces connect a selected surface with the related dimension manipulator end, the offset results for the surface obtained along the different chains can contradict each other. Then the dimensioning result may be corrupt. Therefore, it is important to make appropriate manual surface selections. - For each selected surface the sign of the offset is defined so that it will move
in the same direction as the dimension manipulator end to which it is
related.
A surface can be related to one, and only one, of the dimension manipulator ends. For this, first, the dimension manipulator end must be allowed to move. Second, the surface should be linked to the dimension manipulator end over a chain of adjacent selected surfaces. Third, in the case when the surface is linked to both dimension manipulator ends which are allowed to move, the surface will be related to the end that is closer to it.
As an example, selected surface 2 will have an offset of 0, because cos(90) = 0. The purpose for selection of this surface is just to provide a link from the dimension manipulator ends to the other selected surfaces. Surface 1 is at the moving dimension manipulator end, and surface 3 moves as surface 1.Following the same rules, surfaces 1 and 7 are at the moving dimension manipulator ends. Surfaces 3 and 5 move as surface 1, and surfaces 4 and 6 move as surface 7.