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Since | 20.0 |
Overview ¶
Karma Physical Sky is a node which combines the Karma Sky Dome Light LOP and the Distant Light LOP, to provide a physically-based analytical model of the daytime sky.
The sky model is based on An Analytic Model for Full Spectral Sky-Dome Radiance by Hosek et al.
Creating vs. editing prims ¶
This node belongs to a class of nodes that create or edit USD prims directly. These nodes operate in Create mode or Edit mode. This is controlled by a Create primitives checkbox or a Create/Edit popup menu. In create mode, the node creates new prims. In edit mode, the node changes the attributes on an existing prim. The Edit mode has two variations. Edit will not modify primitives which have a houdini:editable
attribute set to false
. Force edit will modify a primitive regardless of the existence or value of this attribute. This attribute can be set on a primitive using the Configure Primitives LOP.
Parameters that correspond to a USD attribute have a pop-up menu to the left that controls how the node authors the attribute.
In addition to that, any connectable USD attributes (i.e., the ones in the inputs:
namespace) will have menu items that allow disconnecting them from their sources.
Pop-up menu item |
Meaning |
---|---|
Set or Create |
Sets the attribute to the given value, whether it previously existed or not. |
Set If Exists |
Only set the attribute to the given value if it previously existed. Use this mode to make sure an attribute is only set on primitives of the correct type. For example, only |
Block |
Makes the attribute appear to not exist, so it takes on its default value. (If the attribute doesn’t already exist on the prim, this does nothing.) |
Disconnect Input |
Deletes the attribute input connection to its source. Input connections take precedence over attribute values, so disconnecting an input allows the attribute value to take effect. |
Do Nothing |
Ignore this parameter, don’t create or change the attribute in any way. |
Parameters ¶
Intensity
Sets the intensity of both the sun and sky dome lights.
Exposure
Sets the exposure of both the sun and sky dome lights.
Render Light Geometry
Render the sky dome/sun lights directly in the render.
Sun ¶
Angular Size
The visual size of the sun, represented by the angular diameter in degrees. The size of the sun does not affect scene brightness but can be used to achieve soft shadows.
Set Using
You can set sky lights manually through Solar Altitude and Solar Azimuth or Use Location/Date/Time.
Solar Altitude
The vertical angle of the sun in the sky measured from the horizon.
Solaris Azimuth
The horizontal angle along the horizon, where 0
corresponds to the -Z axis.
Enable Sun Light
Creates the sun
Distant Light LOP prim in the scene.
Base ¶
Intensity
A linear scale on the power output of the light.
Exposure
Scales the power output exponentially as a power of 2, similar to an F-stop control. 0 does not scale intensity, negative numbers scale intensity down by the square, positive numbers scale intensity up. Often you will set the Intensity to what looks like the right amount of light, and then use this parameter to “tweak” it.
Color
The color of the light, in energy-linear terms.
Diffuse Multiplier
Scales the effect this light has on the diffuse response of shaders. This is a non-physical “tweak”.
Specular Multiplier
Sampling ¶
MIS Bias
Controls whether multiple importance sampling will sample from the BSDF, the light, or both the BSDF and light.
Sampling Mode
When using the light tree for rendering, Karma will try to put any light source that’s compatible into the tree. This option can force a light to be excluded from the tree and subject to uniform sampling, which can sometimes yield an improved sampling quality the light at the expense of speed.
Sampling Quality
This is the per-light sampling quality, that acts as a multiplier on the global Light Sampling Quality. Increasing the quality will add additional samples for this light source, improving the sampling quality of this light relative to other light sources.
Light ¶
Contributions
Provides detailed control over which BSDF component the light affects.
LPE Tag
Custom label assigned to lights or objects for use with light path expression.
Sky ¶
Turbidity
Measure of the aerosol content of the air which defines the sky appearance.
Ground Albedo
The ground reflectivity that affects the sky color.
Compute Ground Color
Automatically set the ground color based on the Ground Albedo. Turn this option off to set the ground color manually.
Ground Color
The visual ground color as seen in the render.
Horizon Blur Falloff
The angle in degrees below horizon where the sky and the ground color are blended to blur the horizon.
Enable Sky Light
Creates the sky
Karma Sky Dome Light LOP in the scene.
Base ¶
Intensity
A linear scale on the power output of the light.
Exposure
Scales the power output exponentially as a power of 2, similar to an F-stop control. 0 does not scale intensity, negative numbers scale intensity down by the square, positive numbers scale intensity up. Often you will set the Intensity to what looks like the right amount of light, and then use this parameter to “tweak” it.
Color
The color of the light, in energy-linear terms.
Diffuse Multiplier
Scales the effect this light has on the diffuse response of shaders. This is a non-physical “tweak”.
Specular Multiplier
Sampling ¶
MIS Bias
Controls whether multiple importance sampling will sample from the BSDF, the light, or both the BSDF and light.
Sampling Mode
When using the light tree for rendering, Karma will try to put any light source that’s compatible into the tree. This option can force a light to be excluded from the tree and subject to uniform sampling, which can sometimes yield an improved sampling quality the light at the expense of speed.
Sampling Quality
This is the per-light sampling quality, that acts as a multiplier on the global Light Sampling Quality. Increasing the quality will add additional samples for this light source, improving the sampling quality of this light relative to other light sources.
Light ¶
Contributions
Provides detailed control over which BSDF component the light affects.
LPE Tag
Custom label assigned to lights or objects for use with light path expression.
Advanced ¶
Sky Prim Name
The name of the Karma Sky Dome Light LOP prim.
Sun Prim Name
The name of the Distant Light LOP prim.
Sun Light Map
The look-up table used by the node, to give the sun light the correct color and intensity.
Up Axis
The up-axis of the light.
Karma ¶
Active Radius
Artificially clamp the illumination distance from the light. Outside this radius, the light will have no effect.
MIS Bias
Controls whether multiple importance sampling will sample from the BSDF, the light, or both the BSDF and light.
Sampling Quality
This is the per-light sampling quality, that acts as a multiplier on the global Light Sampling Quality. Increasing the quality will add additional samples for this light source, improving the sampling quality of this light relative to other light sources.
Sampling Mode
When using the light tree for rendering, Karma will try to put any light source that’s compatible into the tree. This option can force a light to be excluded from the tree and subject to uniform sampling, which can sometimes yield an improved sampling quality the light at the expense of speed.
Category
The category identifier used to select this light source for illumination.
Maximum HDRI Size
If an environment map is larger than this resolution, it will be scaled down when performing texture analysis. If the map has some very small, very bright values, this filtering may affect how sampling of the environment map is performed.