Reflection and Transmission of Objects Through the Ocean Surface

When external_exact yes has been chosen, the basic ocean input file becomes

RenderWorld_data_file ocean 5 5

n_points_x 512 1

n_points_y 512 1

dx 1.0

dy 1.0

spectrum_file spec1.dat

generate_file yes

random_seed 1451

end

number_aux_oceans 0

number_disturbances 0

box_depth 20.

reference_time 0

surface_type round

radius 6371230

max_distance 100

double_distance 70

wind_type fixed

wind_direction 90

wind_velocity 8

waves yes

water_type 3

external_exact yes

max_distance 2000

image above

reflection_method specular

shadow_air no

glitter no

whitecaps no

textures no

sunbeams no

exclude_items no

number_of_bands 3

band_ids 1 2 3

index_of_refraction 1.34 1.34 1.34

end

Four additional lines are located under the external_exact line. The max_distance is the range from the camera out to which exact reflection and transmission calculations are performed. Beyond that distance, the renderer reverts back to the familiar external_exact no behavior. The choice image above restricts the renderer to reflection/transmission of only those objects (or parts of objects) that are above the water surface. The other choices for image are below, everything, and nothing.

The reflections of skylight and objects from the water surface include the effects of very small waves. Additional control over the ``hardness'' of water reflections is available, via the sharpening_factor and the reflection_method. The sharpening_factor line is conceptually similar to the sharpening factor that can be applied to the glitter, except that here it applies to all reflections and transmissions through the surface. A value of 1.0 on this line includes the effects of the small scale waves on the reflections and transmissions, and corresponds to the default behavior in version 1.0. Other values scale the effect of the small scale waves. A value of 0.0 eliminates the effect of the small scale waves and makes the ocean a perfect mirror. Any positive value can be used, although values greater than 0.1 are recommended for best image quality.

The small scale waves also effect the value of the effective reflection coefficient. The calculation of the reflection coefficient is determined by reflection_method. It has two possible values, specular and averaged. The first value uses the specular value of the reflection coefficient and corresponds to that used in version 1.0, while the second value calculates the reflection and transmission coefficents averaged over small waves. This tends to darken reflections near the horizon and gives a more realistic result.

The air in RenderWorld is fully three dimensional. While the choice external_exact yes allows objects to reflect and refract off of the ocean surface, the air behind those objects is not occluded, and so the skylight reflection is still included. You can fake the effect of object shadowing the air by the shadow_air input. This parameters shodows the air as if it was a skydome surrounding the earth. It has two possible values, yes and no. Answering no has no shadowing of the air by objects, while answering yes enables shadowing. If shadowing is enabled then it is controlled by two additional parameters max_shadow and max_distance_shadowed. max_shadow controls the maximum strength of the shadow. It varies from 0 to 1. If it is set to one then the air is fully shadowed by an opague object. Setting it to a value less than 1 allows some water color to be seen even when the water is fully shadowed. max_distance_shadowed controls the maximum distance away from the ocean that objects will shadow the air. This allows one to have nearby objects shadow the air, but not far away objects such as the cloud.

Here is a sample ascii file that implements these two parameters,