面向爆炸压力场的体绘制自动传输函数设计

直接体绘制广泛应用于可视化领域，其中传输函数决定了最终绘制的效果。大规模爆炸数据属于复杂的时变数据，其压力场的取值范围和分布会随时间剧烈变化。为了实现对冲击波传播特征的连续跟踪，提出了一种基于标量-时间梯度（scalar-temporal gradient，STG）二维空间的自动传输函数设计方法。结合爆炸过程中的物理规律，将STG空间划分为多种状态并总结了状态之间的转移规律。将冲击波的传播特征编码为一段一定长度的状态转移链（state transitions chain，STC），称为时变特征。传输函数中颜色以时变特征为单位，基于完全状态转移链自动分配。传输函数中的不透明度采用基于压强变化速率的分段非线性曲线，凸显压强变化剧烈的特征。选取了两类典型的大规模爆炸场景对方法进行了验证，绘制结果中都包含了丰富的明显可区分的冲击波传播特征。结果表明，生成的传输函数在整个时间维度上都能稳定、准确地捕捉冲击波的传播特征。

Volume rendering automatic transfer function design for explosion pressure field

Direct volume rendering is widely used in scientific visualization. The transfer function largely determines the effect of rendering results. Explosion data is large-scale complex time-varying volume data. The value range and distribution of its pressure field will change drastically with time. In order to realize continuous tracking of shock wave propagation characteristics, this paper proposed an automatic transfer function design method based on scalar-temporal gradient(STG) 2D space. Combined with the physical laws in the explosion process, the method divided the STG space into multiple states and summarized the transition laws between states. It encoded the propagation characteristics of shock waves with state transition chain(STC) of a certain length, called time-varying features. The color assignment in the transfer function took time-varying features as the basic unit, which was done automatically through a complete state transition chain. The opacity in the transfer function used a piecewise non-linear curve based on the pressure change rate, highlighting the characteristics of severe pressure changes. The paper selected two typical large-scale explosion scenarios to verify the method. The rendering results all contain a wealth of clearly distinguishable shock wave propagation characteristics. The results show that the generated transfer function can stably and accurately capture the propagation characteristics of shock waves in the whole-time dimension.