Isophote display mode

Isophotes are displayed as a banded pattern on the surface. The shape of the pattern is a powerful aid to judging surface quality. The isophote display is selected using DISPLAY \ PATCH \ ISOPHOTES or .

Isophotes help the user improve localised surface smoothness by highlighting discontinuities across boundaries between adjacent patches. Isophote bands exhibit one degree of continuity less that of the surface. In other words, a break in isophote bands implies a knuckle (tangent discontinuity), and a knuckle in the isophote bands implies a curvature discontinuity (see Figute 3:117 below).

Figure 3:117. How isophotes highlight discontinuities.

The fairness of larger surface regions can be judged by observing the general shape of the isophote pattern - a fairer surface will exhibit fewer undulations in the isophote bands. A methodology for using isophotes to improve surface fairness is presented in Manual Fairing.

Figure 3:118. Isophote display settings on the Patch Display Settings dialog.

Isophote display settings are found in the Isophotes group of the Patch Display Settings dialog (see Figure 3:118 above). To use these effectively it is necessary to understand how isophotes work. The colour or any point on the surface is proportional to the angle between the surface normal and an incident direction vector (specified in the Direction group). The angles lie between 0 and 180 degrees, therefore each band represents a range of angles roughly equal to 180 degrees divided by the value set in Number of Bands. A larger number of finer bands are less likely to miss surface irregularities, however, the pattern may become difficult to discern if too many are used. The Colour Scheme list allows the user to select one of three repeating colour band patterns. Four colours or Rainbow are generally preferable to Black and White.

Because the isophote pattern depends on the incident direction, a number of different directions should be used when assessing a surface (see Figure 3:119 below). As general guidance, irregularities become more apparent as the angle between the surface normal and the incident direction tends to 90 degrees.

Figure 3:119. Different isophote directions reveal different surface characteristics.

Isophotes are displayed as though they were applied to the surface with a glossy paint - the shiny effect this produces is helps the user judge the general shape of the surface.