@@A scalar value is nothing more than a value that ranges from 0 to 1 (it's in the docs). It applies to parameters that require this kind of values.
Not quite. here are all the mental ray data types as seen in the rendertree (as defined by mental images):
1) Boolean: A variable that can have only two possible values. Usually represents true/false or on/off. The meaning of the two values is arbitrary and for you to decide.
2) Integer: Any whole number. Examples: 1, 2, 3, 457876, 0, -765, etc... Integers do not have fractional components (eg: no decimal point)
3) Scalar: A superset of an integer and is any real number that represents size/magnitude of something (consult a physics book for a more precise definition). However in software it's usually defined as any value that contains a decimal point. Examples: 3.14159, -99999.343238783, 1.0, -58.63, 2.718, 0.00000000000067, etc...
4) Vector: The combination of 3 scalars where each scalar represents a size/magnitude in a particular direction. In XSI vectors are represented as X, Y, and Z, but in the real world, a vector can be the combination of 3 scalars representing any 3 distinct directions (eg: north/south/east, or up/down/left, etc....). Vectors are primarily used to define the orientation or position of something, but have other purposes as well.
One important quality about vectors is that they can be perceived as a point or a line depending on it's use. Example: the vector (3,4,5) can be a point which is 3 units away from the origin in X, 4 units from the origin in Y, and 5 units from the origin in Z. But it can also be thought of as a line that starts at (0,0,0) and ends at (3,4,5). Also, if thought of as a line, it's important to note that vectors are independent of world position - that is, the vector can exist anywhere in space as the only iron clad qualities it has are size (length) and direction (which way it's pointing). Where it's located has no effect on size or direction. I'll leave the math and other advanced topics for another day.
5) Matrix: A combination of numbers that form a matrix (grid). In 3D softwares, matrices are usually a combination of vectors that represent the XYZ axis of an object along with any position, rotation or scaling offsets. Matrix dimensions are very arbitrary and vary upon use. Again, I'll leave the discussion for another day.
6) Color: A combination of 4 scalars that describe the Red, Green, Blue, and Alpha components of a color (RGBA). Very similar to a vector in math terms.
7) Texture: A value that is the combination of both a color and a vector. The vector portion describes location or offset of the color within the source. Used mostly to extract information from a bitmap image (such as a particular pixel's color).
Hope this helps,
Matt
Matt Lind
Animator / Technical Director
Softimage certified instructor:
Softimage|3D
Softimage|XSI
speye_21@hotmail.com