This section describes each button on the edge tool
Sigma The parameter of the gaussian convolution profile used to smooth the image prior to the gradient calculation. It essentially selects the scale of the edge detector. Precision The ratio of the smallest stored value of the guassian convolution profile with respect to the largest. Lower values give increased precision, larger convolution masks and increased computation time. Lower thres The lower contrast threshold (see above discussion). Upper thres The upper contrast threshold (see above discussion). Length thres A lower threshold on the lenght of connected edge strings. Shorter sstrings are eliminated.
Geom2 Options :
2D Geom Fit poly: standard polygonal approximation algorithm. linear: recursively identifies the current longest straight section, segments it, and applies itself to the remaining sections. The actual line fit is done by orthogonal regression. Sections between straight lines found by "linear" are fit by "poly". conic: recursively identifies the current longest conic section, segments it, and applies itself to the remaining sections. The actual conic fit is done using the bias corrected Kalman filter. Sections between conics are fit by linear. All conics are coerced to be ellipses. linear/conic: [default] first applies linear, then emplys a few heuristics to identify groups of neighbouring straight sections that could be conics and applies conic to underlying edge string. Any conics that are found are extended if possible into neighbouring straight lines and/or conic sections (each new section must be absorbed as a whole). This results in unique descriptions for each edge string as either a straight line or conic section. 2D Options join: after initial fit, try to combine conic sections with other conics and/or straight lines that were not necessariliy neighbouring on, or even from, the same underlying edge string.
Geom2 Parameters :
Low fit thres Lower threshold or primitive fitting in pixels. Can be sustained for short deviations of edge strings from primitive. Up fit thres Upper threshold of primitive fitting in pixels. Can not be violated.