Transparency

AlanG · 26 Aug 2011, 07:12

I have a problem with components showing through other components placed on top of them...rafter lines showing through roofing material for example. Anyone tell me how to get them not to show through? Ta

Rich O Brien · 26 Aug 2011, 07:46

Is your roof geometry thin? SketchUp will displaying the underlying geometry when the item that's over it has little thickness. You may not see this up close but as you zoom out the underlying geometry can 'sparkle' through.

AlanG · 26 Aug 2011, 07:53

thanks Rich...yes i'm using steel sheeting 16mm thick - is there no way around this

Alan Fraser · 26 Aug 2011, 07:55

If your roofing material is simply a single skin placed on top of the rafters, then the rafter lines will, indeed, show through...because they are effectively sharing the same space. You will need to give the plywood, tiles, shingles etc. some thickness between the underside that connects to the rafters and the outside surface.
Even then (depending on how far you zoom out and also the thickness of the roof) you may see rafter lines eventually appear as you get further away. This is a display problem associated with OpenGL.

You notice that the black edges on an object don't get any thinner as it gets further away. This in turn means that the edge is the apparent thickness of a human hair if you are right up close, but maybe as thick as a pillar when a long way off. If your roof is fairly thin, then as you zoom out there may come a point where that thickness is exceeded by the apparent thickness of the rafter edges and they'll begin to show through. In this case, the only recourse is to either make the roof thicker, hide the upper edges of the rafter...or just turn off edges altogether.

AlanG · 26 Aug 2011, 08:01

thanks...maybe I could delete the frame for drawings where the appearance of the outer material is important

Gaieus · 26 Aug 2011, 08:03

To rephrase Alan's explanation: SU uses vectors to draw the lines (now we are not speaking about sketchy edges) and these vector lines are always displayed at 1 pixel thickness on screen. When you zoom out enough for your 16mm thick sheeting to be displayed in a thinner screen space than 1 pixel, this bleed through will start.

If it does not bother you too much when modelling, there is a certain solution for your final output (say still 2D export): if you export in a larger resolution, those 16 mms may become thicker than 1 pixel in the image again and this bleed-through may disappear. Try it if it works: zoom out just enough for them to appear and then export at least 2X of your screen resolution.

In exterior scenes, when you are far away from the model, you can even try to hide those rafters altogether (put them on a layer provided they are groups or even more preferably components) and turn that layer off when taking faraway shots.

AlanG · 26 Aug 2011, 08:07

ah ha...layers...I have not really used or explored them yet. I will go back to the manual and learn how...many thanks
Alan

Gaieus · 26 Aug 2011, 08:17

OK, so very basically about layers:

Always group your geometry (or make a component) and only assign these groups/components onto any other layer than Layer0 (otherwise you end up with a mess)
Do not even change the active layer to anything other than Layer 0 (same reason).
Never draw anything on any other layer than Layer 0 (same reason - you can only draw on it if you make it active anyway)
See the video about problems if you do not do so.

If you use layers to control visibility, you can create scenes where some layers are hidden while others are shown then other scenes with other layers hidden etc.

[flash=600,400:14mu6v5p]http://www.youtube.com/v/fBdP499iw0Y?version=3[/flash:14mu6v5p]

Alan Fraser · 26 Aug 2011, 08:20

If you're new to layers, just be aware that they are not the same in SketchUp as they are in, say, AutoCAD...they don't separate geometry. They are generally only used for selective visibility/invisibilty of the kind that Csaba just described.
The Golden Rule is to make sure that you actually draw everything on the default layer, then group it or make it a component before moving it to another layer.
If you actually change your active layer from the default and start drawing on another one, you'll quickly end in a horrible mess with geometry all over the place...maybe faces on one layer and some or all of the edges defining those faces on another layer...then both of those grouped together and moved to a third layer. It can get very ugly very quickly