True Dimensionality: Linear
how many dimensions is enough? > 2 or 3?
knee in error curve
example: measured materials from graphics
linear PCA: 25
can get physically impossible intermediate points
[A Data-Driven Reflectance Model, SIGGRAPH 2003, W Matusik, H. Pfister
M. Brand and L. McMillan, graphics.lcs.mit.edu/~wojciech/pubs/sig2003.pdf]
43