Controlling model lighting

Context:

The default settings provide good contrast for viewing all features in most models. Using the default settings is particularly important for tessellated, banded contour plots, for which intense light can fade the colors in the facets of the contour plot and display misleading results that do not match the colors in the plot legend. These changes to contour colors can also appear in printouts of banded contour plots if you print to file in EPS, PostScript, or SVG formats, because these three formats use tessellated contours by default. To print a banded contour plot to any of these formats without creating misleading contour colors, turn off shading before printing.

Global settings

Ambient light is applied evenly to the entire scene and brightens a model from all directions. Low intensity ambient light allows the positional lighting to create shading that distinguish small features and surface contours from the rest of the model. High intensity ambient light removes shading and may make some model features difficult to see.

If your computer's graphics card supports OpenGL shading language (GLSL), Abaqus/CAE also reveals the global Shading options, from which you can enable Phong shading for your session. Phong shading renders more realistic shading on three-dimensional surfaces than the default option, Gouraud shading, but it can cause a noticeable performance impact on some systems. This performance impact occurs only when the mesh is hidden; if the mesh is displayed (either during modeling or postprocessing), Abaqus/CAE renders Phong lighting with no noticeable performance impact.

Shininess is the reflectivity of the model surface and is used to control the size of specular highlights from the positional lights. A very shiny surface reflects light like a mirror—the light reflects in one direction based on the incident angle of the light source. Therefore, a surface must be positioned correctly with respect to the light source to reflect light to your viewpoint. Surfaces that are less shiny reflect light more randomly, so a wider range of surface angles can reflect light to your viewpoint. Like high intensity ambient lighting, low shininess can obscure small features and contours of your model from view.

The Viewpoint option controls how specular lighting effects are calculated. An Infinite viewpoint assumes a constant vector for the direction from the camera to each point when calculating reflections and specular highlights at a point. A Local viewpoint calculates a separate direction vector for each point based on its position in the viewport. A Local viewpoint creates more realistic lighting effects but can decrease overall performance.

Positional light settings

Positional lights provide a light bulb effect. A positional light is projected onto the model from the specified location, and its effects change as you rotate your model view. Positional lights work in conjunction with shininess to determine how your model reflects light.

The distance of the light from the model is equal to the distance from the camera to the model. You can position the lights by specifying their Latitude and Longitude on a hemisphere around the model. You can also specify the Type of light source being used. A Directional light is a planar light source; the angle of incident light on the model will be equivalent for all parallel surfaces. A Point light is a point light source; the angle of incident light depends on the location of the surface or point relative to the light. A Point light creates more realistic lighting effects but can decrease overall performance.

You can control two different qualities for positional lights: Diffuse intensity and Specular intensity. The Diffuse setting controls the intensity of a positional light. Unlike ambient light, surfaces that face toward the light position will brighten more readily than other surfaces in the model when increasing the diffuse intensity of a positional light. The Specular setting controls the brightness of those surfaces that are reflecting from the light toward the viewpoint. You should first set the position and diffuse intensity of the positional light to achieve the shading you desire. Then you can adjust the brightness of reflected light with the Specular slider.