"Components", "solids" and shut lines


#1

Hello

Okay I give up - what exactly does Sketchup mean by “a solid”? Does Sketchup think in terms of surfaces or 3D solids

And what does it mean by “a component” - which should I convert things into “components”?
And what about “Groups”.

I just need to get my head around the basic concepts!

e.g. I have just done some extrusions of shapes through each other. But I cant get rid of the join lines that were left behind between the extrusions.

The point is that some of these lines are on flat surfaces and so should no longer exist.
i.e. If I triple click on the object the whole object is selected, so Sketchup clearly thinks that it’s all part of the same item, no?

I can just go and delete the ‘shut lines’ there were left over manually, but will Sketchup complain later if I do that (as it feels like a very odd thing to be doing…)

Is there a way to always work in solids if so is there a downside to this?

Thanks


#2

SketchUp is a surface modeler. SketchUp’s solids aren’t solid in the way that shapes are filled with “material”. Close 3D shapes are hollow.

SketchUp uses edges to bound faces. Multiple faces can bound a 3D shape. But unless grouped you are still dealing with just the basic edges and faces.

[quote=“ship69, post:1, topic:17016”]
… i.e. If I triple click on the object the whole object is selected, so Sketchup clearly thinks that it’s all part of the same item, no? [/quote]
Not necessarily. This means that by tripple clicking you select all connected basic edgesand faces. Right click on this selectionand select ‘Make Group’ or ‘Make Component’. Only then SketchUp will recognize the selection as one entity: group or component.

Only groups and components can be SketchUp Solids.
That is if they meet certain requirements.
A SketchUp Solid is a closed shape with no gaps in its surface and no geometry inside.
Each of its edges thus has only two faces that it partly bounds. Say like a balloon that only holds air, nothing else inside.


#3

OK… so what’s the difference between a Group and a Component?

Also if Sketchup can think in terms of Solids, dos that not make it a solid modeler (as well as being a surface modeller)?

Btw, to get clear an “Edge” is like a line - e.g. between two points (in 2 or 3 Dimensions), yes?
And a “Face” is a “surface” - a continuous set of points (in 2 or 3 Dimensions) that has length and breadth but no thickness, yes?


#4

A group is a collection of entities. If you make a bolt, for example, you can group the geometry and place copies of your bolts here and there. However, each group is a separate set of duplicate geometry. A component is exactly like a group except that it is only defined once. Each copy is only a reference to the geometry with enough information to place it and scale it. If you edit a component, all the copies will change as well. This is handy if you want a 12mm bolt and later want it to be a 13mm bolt. If one of your components needs to be different, you can make one of the components into a “unique” version and from then on, it is no longer linked to the previous definition. Its copies will then become a separate set of components. A group can not only contain geometry, but other groups as well (or sub-groups, for that matter). A flywheel might have several groups that make up the separate pieces and then all of them would be grouped to be the flywheel. Also, a group or component can later be “exploded” to remove the outer layer of grouping.

Technically speaking, Sketchup is a surface modeler, but only for planar surfaces. It does not natively support other surfaces such as ruled surfaces, surfaces of revolution, b-surfs, etc. However, each of these surfaces can be approximated by a mesh of planar “facets”. Similarly, SketchUp is not a solids modeler since it has no native primitives such as a sphere, cone, cylinder, etc. However, once again, each of these can be approximated with a mesh of planar facets. If the mesh follows certain rules and encloses a closed volume, then it is considered a “solid” and will treated as such by 3D printing systems.

A line is called an edge in SketchUp. A circle is defined by points, but is technically a series of edges (or segments). An arc with 6 edges will be defined by 7 points. The more points, the smoother the arc, but SketchUp will “smooth” or “soften” them to make them look very smooth when rendered visually (not so much when 3D printing). BTW, under the hood, a circle or arc can be later edited to change the radius or the number of edges … once it has been “exploded” however, it will turn into a series of separate edges and no longer act like a single unit.

A face is a planar surface bounded by a closed loop of edges. When you create a closed loop (like a circle) SketchUp will automatically fill in the planar surface. Due to using a plane as the underlying geometry, most intersections and other 3D manipulation is very fast due to the math involved dealing with direct solutions.


#5

Groups are one of a kind chunks of geometry.
Components are for repetative use. Change one instance of a component and all same instances (say copies) will follow the changes.

See an edge as a finit line, running between its two endpoints.
A face is a special surface, it is two dimensional, all in one plane.
A SketchUp surface is made up of more than one face, Most often all not in one plane.
A face (and a surface) has no thickness.


#6

All interesting. Thank you. :slight_smile: