PRIMER 22.1

Path Visualisation Tab: Controlling What Is Shown During Advanced Path Editing

The advanced editor mode adds a lot of detail to the path, which can lead to the display getting quite congested.

The "Path Visualisation" tab of the Fitting Options panel contains controls that allows you to control what is displayed, both cutting down excess detail and making it easier to see what you are doing in confined geometry.

Hint : in PRIMER 18 onwards the Cut Section panel can be undocked to become a "floating" panel, meaning that both it and other operations such as this can be active at the same time. This can be a very helpful feature when trying to fit explicitly meshed seatbelts to tight geometries.

Path order controls the path curvature between points when trying to navigate tight geometries.


Linear (straight lines)	Mixed (50% straight, 50% spline)	Spline (continuous cubic spline)

The path order will make very little difference to the final shape after form-finding, but typically a spline works best for the typical "simple, rubber band round an egg" case of an adult geometry, and linear or mixed are often better when trying to navigate tight geometries.

Path drawn as controls how the "elements to be made" are draw


Skeleton wire (wireframe, no thickness)	Thick wire (wireframe, showing thickness)	Thick shaded (Shaded, showing thickness)

Shaded geometry tends to look the most realistic, but wireframe is sometimes useful if you want to look "through" the belt at underlying structure. See also the transparency setting below for belt path symbols.

Showing can be used to limit which segments of a belt are displayed.

In tight geometries, such as this example of the pelvis buckle region of a child in a child seat, it can be difficult to see the "behind" section of belt.

For example point 8, on the "exit" side of the buckle, is partially obscured and changing the view will not help much.

By restricting display to only one of these segments, here #2 which passes over the lap section, it becomes a lot easier to see what you are doing.

In these situations it is usually best to sort out the "behind" path nearest to the dummy first, then worry about the "in front" one on top.

You can select the path segment to show explicitly by typing in its number, or by using the [+] and [-] buttons to cycle back and forth along the belt.

Drag handles. The arrows that let you translate belt points in space.

Display of drag handle arrows can be toggled on/off using the tick-box in this diagram.

To use these move over an arrow head until it "lights up", then click with the left mouse button and drag in the relevant local direction. (There is no drag action associated with the right mouse button.)

Left mouse action
	Along the belt (forwards)	Along the belt (backwards)

	Transversely	In/outwards

The reason that "along the belt" dragging, red arrows, is split into separate forwards and backwards directions is because the natural (spline) curvature of the belt can be "broken" in this direction to give sharp changes in direction. This is explained under Twist handles below.

It is also possible to drag the basic path point itself, and unlike the drag handles above this dragging takes place in the 2d plane of the screen.

Left
mouse
action

Hovering the mouse over the
light blue symbol at the point

Highlights it in yellow, then you
can free drag in 2d screen space

Warning!! Dragging the path point in any of these directions will disconnect it from any node that might originally have been used to define it. This does not matter in itself, but it may mean that a subsequent Auto Refit fails to track movement of the underlying structure.

Twist handles. The cube symbols that let you adjust path direction and twist at a point.

Display of twist handle cubes can be toggled on/off using the tick-box in this diagram.

As above hover over a cube symbol until it "lights up", then click and drag to twist the path. The direction in which the point moves depends on the mouse button used, as show in the images below:

Left mouse action
	Up/down forwards rotation about transverse (green) axis This breaks the path curvature	Up/down backwards rotation about transverse (green) axis This breaks the path curvature

	Twists the path about the long (red) axis.	Rotates whole path, ie both red arrows, about transverse axis

Right mouse action
	Skews forwards path direction in plane about outwards (blue) axis This breaks the path curvature	Skews backwards path direction in plane about outwards (blue) axis This breaks the path curvature

	Skews whole path about the outwards (blue) axis. This breaks the path curvature	Twists the path about the long (red) axis. (Redundant capability: same as left mouse on green above.)

These diagrams look rather complex. In practice it is actually quite intuitive since the shape of the path changes dynamically as you drag, so the best way to understand this is simply to experiment with it. Remember that the middle mouse button can be used to "undo" previous actions.

The meaning of " Breaking the path curvature " is explained below.

Understanding belt path curvature.

The various twist controls above allow you to control the shape of the belt by adjusting path curvature. The following images explain how this works.

The initial status when you first create a belt path.

In this example we have a very simple path of just three points.

The shoulder
Middle of chest
Pelvis

The basic path, drawn in blue here, is the series of straight lines between these points.

The derived curvature, drawn in black here, is the "natural curve" fitted through those points. Mathematically it is a cubic spline, permitting continuously varying curvature through any number of points.

The belt path, grey here, is the natural curve projected outwards, with a "width" direction determined either from the orientation of the underlying elements or from the path curvature. "Outwards" is also determined from curvature and the underlying elements.

Adjusting the natural curvature

Here the curvature at point 2 in the middle of the chest has been adjusted as follows

The path has been rotated "downwards"

This was done by clicking on the blue twist handle (blue cube) and dragging it down in the direction of the yellow arrow as drawn here. The effect is to rotate the natural curvature at the point.
The path has also been twisted towards you, the viewer.

This was done by clicking in the green twist handle (green cube) and dragging it from left to right in the direction of the red arrow as shown here.

In both cases it is evident that the slope of the path through point #2 has changed but the path is still a continuous curve through the point.

Breaking the natural curvature

Here the red twist handles (red cubes) along the path of the belt have been used to "break" the natural curvature.

The upper handle has been dragged forwards

This makes the path a bit more vertical above point #2
The lower handle has been dragged upwards.

This brings the lower section of the path up and points it outwards from the chest of the dummy.

It is clear that there is no longer a continuous curve through point #2, rather there is a sharp change of slope. This is referred to as "breaking" the natural curvature and it is very useful when you need to feed the belt path through tight geometries.

Note that from v20.0 onwards, the red twist handle opposite to the one being dragged will be locked to it's original orientation resulting in a cubic spline shape of the path between the two delimiting points. This behaviour makes it easier to feed the initial path through tight geometries.

The following example shows the effect of this change if the red handle at point 1 has been dragged upwards in PRIMER v20.0 versus earlier versions.

Twisting the belt in plane, "skewing" it.

The examples above use [left mouse click] + [drag handle] which tends not to alter the in-plane twist of the belt.

It is also possible to use [right mouse click] + [drag handle] to alter the in-plane direction of the belt at a point. In this example the two red drag handles (cubes) above and below point #2 have both been moved from left to right as seen here.

This has the effect of "skewing" the path, also breaking natural curvature.

This looks awful , but don't worry! Form-finding will sort it out.

No natural belt would adopt this shape, and if you look carefully you'll see that the width is wrong close to the point as well. This doesn't matter: during the form-finding "fit" process the belt will tend to pull back to a natural line and the correct width.

Intermediate points showing the interpolated points between basic path points. Intermediate points can not be dragged, but a right click on them allows you to create a new basic path point at their location. This can be very useful when you need more control over a section of path as the intermediate point will already be in the right place for the new basic point.

Path transparency Allows control over the effective transparency of the belt path.

This transparency setting only applies to the visibility of belt path drag and twist handles through the belt itself, not to the visibility of the rest of the structure through the belt.

The reason for it is that often you want to get at a handle that is "behind" the belt path. You know it is there, but without some degree of transparency it is impossible to see it , the left hand case above. Full transparency, the right hand case above, looks a bit misleading as it defies depth perception. So the default is the 30% case, in the middle above, which gives a good compromise between visibility and intuitively correct depth perception. You can control the extent of this transparency using the slider and save your current setting for future sessions.

Max handle length controls the upper size limit of drag and twist handles

Drag and twist handle sizes scale with the model scale factor, but are subject to an upper size limit to avoid the plot becoming too crowded with symbols. The default upper limit on size is 400 screen space units, which is about 10% of the window width. (Screen space is notionally 4096 wide, regardless of window pixel resolution.)