Drawing accuracy measured using polygons

The study of drawing, for its own sake and as a probe into human visual perception, generally depends on ratings by human critics and self-reported expertise of the drawers. To complement those approaches, we have developed a geometric approach to analyzing drawing accuracy, one whose measures are objective, continuous and performance-based. Drawing geometry is represented by polygons formed by landmark points found in the drawing. Drawing accuracy is assessed by comparing the geometric properties of polygons in the drawn image to the equivalent polygon in a ground truth photo. There are four distinct properties of a polygon: its size, its position, its orientation and the proportionality of its shape. We can decompose error into four components and investigate how each contributes to drawing performance. We applied a polygon-based accuracy analysis to a pilot data set of representational drawings and found that an expert drawer outperformed a novice on every dimension of polygon error. The results of the pilot data analysis correspond well with the apparent quality of the drawings, suggesting that the landmark and polygon analysis is a method worthy of further study. Applying this geometric analysis to a within-subjects comparison of accuracy in the positive and negative space suggests there is a trade-off on dimensions of error. The performance-based analysis of geometric deformations will allow the study of drawing accuracy at different levels of organization, in a systematic and quantitative manner. We briefly describe the method and its potential applications to research in drawing education and visual perception.