The frontal area can be calculated with the following CEL: IntegrationVariable = Normal X/abs(Normal X + 1e-8) FrontalArea = 0.5 * areaInt_x( IntegrationVariable )@Body This example CEL is for the frontal area in x-direction. With areaInt_x the integral of the area components in x-direction multiplied with an integration variable Phi is obtained. To obtain the area in x-direction, the integration variable must have a value of 1. However, as the x-component of the areas has a sign, the expression areaInt_x(1)@body will result in a value of zero for a closed surface. So use the integration variable Phi = Normal X/abs(Normal X) to obtain a +1 or -1 depending on the local area, and hence to obtain the integral of the absolute values of the area x-component. The small number is just required to avoid division by zero for area that have no x-component. The result is the double of the frontal area, so include the 0.5 to get the correct frontal area. Note that this approach works only for convex surfaces.