Contents random_number_seed line has disappeared. This will save a few seconds of computer time.
RenderWorld_data_file ocean 5 5
n_points_x 1024 1
n_points_y 1024 1
dx 0.1
dy 0.1
spectrum_file spec2.dat
generate_file no
end
number_aux_oceans 0
number_disturbances 0
box_depth 20.
reference_time 0
surface_type round
radius 6371230
max_distance 100
double_distance 60
wind_type fixed
wind_direction 90
wind_velocity 8
waves yes
water_type 3
external_exact no
glitter yes
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
We turn on glitter by changing
no to yes on the glitter line. This will slow the code down (typically about 20%), but adds dramatically to the realism of the image if the camera is facing toward the sun. The setting yes in conjunction with the line external_exact no calculates glitter for a sunlight which is only affected by the air, and ignores any other objects which might be present. When external_exact has other values their can be an impact on glitter. This is discussed in more detail in the section ``Reflection and Transmission of Objects Through the Ocean Surface.''
A second option for the
glitter line is yes_exact. With this option the glitter is calculated as before, but other objects present in the scene may attenuate the sunlight, depending on their properties and the glitter geometry. This allows you to keep the computational burden of objects reflecting in the water low (via external_exact no) but have the glitter shadowed properly by those objects.
The choices
glitter yes and glitter yes_exact invoke a sophisticated rendering algorithm somewhat tuned to the conditions on the earth. To have more control over the character of the glitter, a third choice, glitter enhanced exists. The examples in the section demonstrate how to use it.
The concept behind enhanced glitter is to provide the user with the flexibility to modify the local structure of individual spots of glitter. The entire glitter field in an image is the sum of many distinct glitter spots. The
enhanced option divides a glitter spot into two components: a central core of high intensity, and an ``aureole'' of falling intensity around the core. This allows the user to separately control these two components as a function of angle in the camera plane. The method of control manipulates the width of a glitter spot in the image plane by controlling the roll-off from the center, and by clipping the outer edge of the glitter spot. In addition, the core of the glitter can be assigned arbitrary brightness and color.
The first example below is an ocean file with the
glitter enhanced in its simplest option. This ocean file is like other ocean files, except that between the glitter line and the whitecaps line an additional four lines have been introduced.
RenderWorld_data_file ocean 5 5
n_points_x 1536 1
n_points_y 1536 1
dx 0.5
dy 0.5
spectrum_file spec.dat
generate_file yes
seed 1011
end
number_aux_oceans 0
number_disturbances 0
box_depth 20.
reference_time 0
surface_type flat
max_distance 180
double_distance 200
wind_type fixed
wind_direction 160
wind_velocity 10
waves yes
water_type 3
external_exact no
glitter enhanced
sharpening no
sharpening_factor 2.0
prob_threshold 0.5
saturation 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
The first inserted line is
sharpening no. This indicates that the glitter enhancement is global over the entire ocean surface. The sharpening yes option is discussed later for allowing the enhancement to be dependent on ocean position. The line sharpening_factor 2.0 provides the degree to which the width of the glitter spot is changed. Values greater than 1 actually broaden the spot, whereas values less than 1 sharpen it. A value of exactly zero will cause problems, so do not use it.
The glitter spot can also be clipped, so that below a threshold of the width of the spot, the glitter is removed. The line
prob_threshold 0.5 performs this clipping. The value 0.5 specifies the fraction of the spot width at which to perform the clipping.
The options for the
saturation line control adjustment of the core of the glitter spots. The setting saturation yes allows the user to artificially boost or suppress the central region of a glitter spot. After specifying yes, an additional four lines are inserted after the index_of_refraction line. The first of these lines, saturation_band 1, determines which band is used to compare the criteria for the existence of a glitter spot core, in this case it is the red band.
RenderWorld_data_file ocean 5 5
n_points_x 1536 1
n_points_y 1536 1
dx 0.5
dy 0.5
spectrum_file spec.dat
generate_file yes
seed 1011
end
number_aux_oceans 0
number_disturbances 0
box_depth 20.
reference_time 0
surface_type flat
max_distance 180
double_distance 200
wind_type fixed
wind_direction 160
wind_velocity 10
waves yes
water_type 3
external_exact no
glitter enhanced
sharpening no
sharpening_factor 2.0
prob_threshold 0.5
saturation yes
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
saturation_band 1
saturation_threshold 500.
sub_saturation_scale 0.5 0.5 0.5
saturation_value 1000. 1000. 1000.
end
The
saturation_threshold parameter is the intensity of reflected glitter light in the saturation_band at which a glitter core is declared. All larger intensities are also in the core. Upon declaring a glitter core, the intensity in all channels in the core is given by the set of intensities in saturation_value. If glitter light does not lie in the core, the set of parameters on the line sub_saturation_scale will scale the intensity in each band.
In the next example below, the glitter core
saturation controls have been turned off, but the sharpening option has been changed to yes to allow the user to change the sharpness of the glitter as a function of angle. In this case, instead of giving a single sharpening factor as before, a file name leads to a ``key-frame style'' list of sharpness as a function of angle in the camera plane. An example of the file is listed after the ocean file. When an angle between those in the sharpening.dat file are needed, RenderWorld interpolates to get the value.
RenderWorld_data_file ocean 5 5
n_points_x 1536 1
n_points_y 1536 1
dx 0.5
dy 0.5
spectrum_file spec.dat
generate_file yes
seed 1011
end
number_aux_oceans 0
number_disturbances 0
box_depth 20.
reference_time 0
surface_type flat
max_distance 180
double_distance 200
wind_type fixed
wind_direction 160
wind_velocity 10
waves yes
water_type 3
external_exact no
glitter enhanced
sharpening yes
file sharpening.dat
prob_threshold 0.5
saturation 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
The file
sharpening.dat is as shown below:
number_of_times 3
angle sharpening_factor
90 1.0
100 2.0
110 4.0
end