gifStrut and Hub Intersections Part 2 - Intersection Rules

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After implementing Cupolas and Extrusions, it became necessary to calculate intersections with not only the hub circumference but also its top and bottom. Consequently the height of the intersection cylinder used by the algorithm has been set to the Hub depth.

In previous versions, the height of the intersection cylinder was 30 x the hub depth; the reason for this was to avoid intersection errors when the hub was above or below the quad-edge center line; it also accounted for spaceframe edges which enter the hub at highly acute angles.

However, as from version 0-9-6, you must ensure that the hub depth is sufficiently large to intersect with all non-spaceframe edges meeting the hub circumference. If the hub depth is too small, and the intersection fails, Geodesica will then test for top and bottom intersections with the hub - and this is the required behaviour for intersecting struts with hubs around a Cupola...

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Above: Hub Intersect is ON and the Hub Ingress has been set to 1 inch. The new algorithm ensures that hub intersections do not fail for vertical struts around a cupola.

Spaceframe Intersection Options

Because spaceframe struts always enter a hub at highly acute angles, they now have their own intersection cylinders which are typically much longer than the actual hub depth. This allows spaceframe intersections to form correctly, just as before. The Hub Axis Shift feature can then be used to align the hub with spaceframe struts and their corresponding hub flanges.

However, if this behaviour is not desired, and you want spaceframe struts to intersect with the hub top or bottom, please uncheck the box ‘Elongate Hub Intersection Cylinder’ on the Spaceframe tab of the ‘Struts and Hubs’ window.

Hub Plane Intersection Options

As is required of Cuploas and Extrusions, strut ends may be projected to the bottom & top disks of cylindrcal hubs.

Addtionally, new code now intersects struts with the tangential planes of spherical and right-angled cone hubs.

CAVEAT 1: If you shift the hub up or down along the hub axis, you must rebuild the struts to intersect with the new planes.

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'Project struts ends to Hub Intersection Plane'

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'Project struts ends to Hub Intersection Plane'
After applying a hub shift.

CAVEAT 2: If you change the radii of a right-angled cone hub, you must rebuild the struts to intersect with the new planes.

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Right angled cone
Base radius greater than Top

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Hub hidden to show intersections.

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Right angled cone
Top radius greater than Base

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Hub hidden to show intersections.

Hub & Strut Intersections in Cross Target Spaceframes

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Above: how to handle hub intersections in a cross-target spaceframe.

This example shows an Eden Project type Dual spaceframe with right-angled cone hubs on the inner manifold. Strut intersection and 'Project struts ends to Hub Intersection Plane' are ON for all struts. In order to make the spaceframe struts intersect with the tops of the right-angled cones in the inner manifold, a hub axis shift was applied to the ORG ends of all spaceframe struts. (The ORG ends start in the Dual lattice of ‘Target A’).