Gonioreflectometer
Encyclopedia
A gonioreflectometer is a device for measuring a bidirectional reflectance distribution function
(BRDF).
The device consists of a light source illuminating the material to be measured and a sensor
that captures light reflected from that material. The light source should be able to illuminate and the sensor should be able to capture data from a hemisphere
around the target. The hemispherical rotation dimension
s of the sensor and light source are the four dimensions of the BRDF. The 'gonio' part of the word refers to the device's ability to measure at different angles.
Several similar devices have been built and used to capture data for similar functions. Most of these devices use a camera
instead of the light intensity-measuring sensor to capture a two-dimensional sample of the target. Examples include:
Bidirectional reflectance distribution function
The bidirectional reflectance distribution function is a four-dimensional function that defines how light is reflected at an opaque surface...
(BRDF).
The device consists of a light source illuminating the material to be measured and a sensor
Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
that captures light reflected from that material. The light source should be able to illuminate and the sensor should be able to capture data from a hemisphere
Sphere
A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...
around the target. The hemispherical rotation dimension
Dimension
In physics and mathematics, the dimension of a space or object is informally defined as the minimum number of coordinates needed to specify any point within it. Thus a line has a dimension of one because only one coordinate is needed to specify a point on it...
s of the sensor and light source are the four dimensions of the BRDF. The 'gonio' part of the word refers to the device's ability to measure at different angles.
Several similar devices have been built and used to capture data for similar functions. Most of these devices use a camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
instead of the light intensity-measuring sensor to capture a two-dimensional sample of the target. Examples include:
- a spatial gonioreflectometer for capturing the SBRDF (McAllister,2002).
- a camera gantry for capturing the light fieldLight fieldThe light field is a function that describes the amount of light faring in every direction through every point in space. Michael Faraday was the first to propose that light should be interpreted as a field, much like the magnetic fields on which he had been working for several years...
(Levoy and Hanrahan, 1996). - an unnamed device for capturing the bidirectional texture function (Dana, et al. 1999).