Complex 3D curves can be created by directly drawing mid-air in immersive environments (AR/VR). Drawing mid-air strokes precisely on the surface of a 3D virtual object however, is difficult; necessitating a projection of the mid-air stroke onto the user "intended" surface curve. We present the first detailed investigation of the fundamental problem of 3D stroke projection in AR/VR. An assessment of the design requirements of real-time drawing of curves on 3D objects in AR/VR is followed by the definition and classification of multiple techniques for 3D stroke projection. We analyze the advantages and shortcomings of these approaches both theoretically and via practical pilot testing. We then formally evaluate the two most promising techniques spraycan and mimicry with 20 users in VR. The study shows a strong qualitative and quantitative user preference for our novel stroke mimicry projection algorithm. We further illustrate the effectiveness and utility of stroke mimicry, to draw complex 3D curves on surfaces for various artistic and functional design applications.

中文翻译：

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在 AR/VR 中在 3D 表面上空中绘制曲线

可以通过在沉浸式环境 (AR/VR) 中直接绘制半空中来创建复杂的 3D 曲线。然而，在 3D 虚拟对象的表面上精确地绘制空中笔划是很困难的。需要将空中行程投影到用户“预期”的曲面曲线上。我们首次详细研究了 AR/VR 中 3D 笔画投影的基本问题。对AR/VR中3D对象实时绘制曲线的设计要求进行评估后，对3D笔画投影的多种技术进行定义和分类。我们从理论上和通过实际的试点测试分析了这些方法的优点和缺点。然后，我们在 VR 中对 20 位用户正式评估了两种最有前途的技术喷雾和模仿。该研究表明，我们的新型笔画模拟投影算法具有很强的定性和定量用户偏好。我们进一步说明了笔画模仿的有效性和实用性，为各种艺术和功能设计应用在表面上绘制复杂的 3D 曲线。