降维图里的空白区域也会失真，这个新指标能发现其他指标看不出的视觉变形，论文不长，想学方法可以看看。
作者提出Gap Index（GI）质量指标，通过将二维投影空间分解为空白三角形，并与高维对应部分比较来计算变形。该指标可以聚合为单一标量值，也可叠加在投影上可视化局部失真模式。实验表明，与常见质量指标不同，GI能捕捉具有高视觉影响的小型结构变形，且计算快速、可解释。
Measuring Distortion in the Empty Regions of Dimensionality Reduction Scatterplots with the Gap Index
Quality metrics play a crucial role in the proper use of dimensionality reduction projections for visual analysis of high-dimensional data. They quantify the degree of distortion of a projection compared to the high-dimensional data and provide a reliable indication of how confident users can be in the structures they see in the resulting layouts. However, most popular metrics focus on capturing direct relationships between points (e.g., distances or neighborhoods) while neglecting distortions in empty areas of the layout, even though these often compose visually relevant features of a 2D layout. In this paper, we introduce the Gap Index (GI), a quality metric for 2D projections that captures visual distortion by measuring spatial distortion in empty areas of a projection. It does so by decomposing the space into empty triangles, which are then compared to their high-dimensional counterparts to compute the deformation. This per-triangle deformation can be aggregated into a single scalar value or overlaid on a projection to visualize regional distortion patterns. Results show that, contrary to popular quality metrics, the GI is sensitive to small structural deformations that have high visual impact. It is also fast to compute and interpretable.