2-D Scalar Field Stratification

Intersecting and overlapping surfaces, which arise in multivariate data display and related applications, are difficult to render effectively. Users find it hard to determine which surface is above and by how much, as well as the shape of the surface underneath. Unfortunately optimal rendering choices for simple overlapping surfaces may not be optimal for intersecting surfaces due to transitions in rendering order. We have developed a rendering strategy in which the attributes at a point on a particular surface are assigned based on surface order in relationship to the other surfaces, independent of viewpoint. Thus, instead of trying to realistically render the appearance of actual intersecting surfaces, our rendering technique is an abstraction that encodes stratification information. Our research includes the creation of a demonstrable prototype, as well as the execution of a study that investigates users’ ability to distinguish surface order, shape and height difference for stratification-based rendering. Our study shows that a stratified visualization of two intersecting surfaces is preferred over a non-stratified version when gel opacity and stroke width are varied according to surface order. We have also found that extreme rendering attribute assignments make surface order easier to determine at the expense of the perception of surface cohesion.