WEBVTT

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We introduce ScaffoldSketch

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a system that makes it possible 
to draw accurate 3D models in VR

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People like to draw in VR because it 
is immersive and the output is in 3D 

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but it's really hard to be accurate

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Previous work has already proved this,  

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more degrees of freedom, lack of 
physical surface, and depth issue

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these all contribute to larger 
errors directly drawing in VR

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So how do people draw accurately in 2D?

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product designers can draw very accurate sketches

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when they draw with pen and paper

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they will first draw construction 
lines or known as scaffolds

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then they will draw the object shape on top

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the scaffolds will serve as visual 
guidance to make the shape strokes accurate

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this is how industrial designers 
can draw an accurate trash can

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there are also related work studying or utilizing 
this scaffold plus shape way of sketching

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Can we borrow this approach directly in VR?

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Even with the help of scaffolds 
people still cannot draw accurately

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the reason is similar as before

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with more degrees of freedom it 
requires higher motion control

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even the scaffolds are not 
perfectly aligned with each other

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if we could eliminate these issues we would 
have a nice way to draw accurately in VR

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We introduce ScaffolSketch
a system helps people draw accurately in VR  

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by auto-correcting scaffolds and shape strokes

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the scaffolds are straight 
lines with special relationships  

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so they can snap to each other based on 
the endpoints, directions, and lengths.

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we also support tick on the scaffold 
lines to mark intermediate positions  

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as designers often do with pen and paper

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here's an example
the black lines are existing scaffolding lines

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when the user draw a new scaffold line 
we can consider these relationships

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however relationships may conflict with each other

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previous attempts to resolve conflicts 
often use heuristics or don't satisfy any

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we resolve with an iteratively 
re-weighed least square scheme

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the weights will be updated after each iteration 

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the more satisfiable constraints 
will be giving higher weights

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and the less satisfied will have smaller weights

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in the end the weights will 
either be infinity or zero  

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that is satisfied or discard for the constraints

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The shape strokes are smooth curves 
or lines attached to the scaffolds

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mainly attached to the endpoints, 
midpoints, or the user marked positions.

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and usually tangent to those points

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for the same scaffold square different user 
input will be auto-correct to different results

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the shape strokes are auto-correct 
based on the scaffolds and 

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the user's drawing

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just like how the 
scaffolds support shape strokes in 2D

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we also support space curves as shown here

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and with more tick marks as intermediate positions 
the auto-correct result will also be different

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once we have the beautified scaffolds, 
now if the user drawn a shape curve

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we can find whether the curve 
is tangent to the intersections  

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thus we can have the curve directions 
and positions at those key points

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the positions and directions are fixed  

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at those points

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but we can change 
the magnitude of the tangents

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different magnitudes of tangents 
will give us different curves

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and our goal is to find the most smooth curve
that is the one of minimal variation of curvature

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and if the curve is not tangent to the scaffolds 

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we will take the directions 
from the original curve

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here is an example of the input scaffolds 
and this is the auto-correct result

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the shape strokes are based on the scaffolds 
and this corresponding auto-correct result

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we did a remote user study with six 
participants: all industrial designers

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they used our system in two conditions: 
within and without auto-correct

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they all expressed that auto correct 
helped them draw more accurately

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and they want to use ScaffoldSketch in the future

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see the paper for details

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limitations and future work, we didn't consider 
surfacing, which is also very important

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the current output is curved networks, 
but surfaces are often needed

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without surfacing it's hard to 
draw details or shading strokes

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and also current shape strokes 
are guided by the scaffolds,  

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so the user cannot draw freeform strokes

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I think with all these features combined 
it will make a better user experience  

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and more vivid 3D models

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In conclusion, ScaffoldSketch enables  

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precise 3D curve drawing by decomposing or 
auto-correct into scaffold and shape stages

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it lets people transfer industrial 
design drawing skills into 3D

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and it resolves conflicting constraints 
with an iterative re-weighed scheme

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thank you