Edge Geom Tool Buttons

This section describes each button on the edge tool

• im rank Pre-process the images to replace each greylevel value with the local rank (within a region typically 11x11 pixels). This process simulates the first order effect of change detection found in the primate retina in a way which produces data with approximately binomial errors. This is sometimes more suitable for input to correlation based stereo matching than raw greylevels.

• im rectify Transform both the left and right stereo images to cyclopean co-ordinates. Don't expect the images to still be centered in the left and right Tvs.

• canny Linked canny edges are obtained, to sub-pixel accuracy, for the selected region of interest. The process is two pass (implementing hysteresis); first the edges with an intensity gradient above a low threshold are identified; then linked edge strings that are entirely below an upper threshold are eliminated ( the remaining edges are displayed in purple with blue termination points).

  Edge paramaters:

  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.
  

• edge rectify Use current parallel camera geometry ( recovered from the calibration files) to update the position of edge data to be consistent with it. The actual storage location of each image is unaffected. This process must be performed prior to stereo matching and 3D geometrical recovery.

• edge derect Reverses the effect of "edge rectify" to return position to the initial coordinate frame.

• geom2 Performs geometrical approximation procedures over each of the linked edges strings identified in the left image.

  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.