[GRASS-dev] some detail questions on i.segment
mlennert at club.worldonline.be
Wed May 18 09:36:13 PDT 2016
I'm working on potentially improbing the i.segment.uspo addon and am
looking at the possibility of including the goodness of fit output map
somehow in the evaluation of the quality of the segmentation.
For that, I need to exactly understand the goodness of fit measure.
As a starter: why is the threshold parameter (globals->alpha) squared
before being used in create_isegs.c (and in the calculation of the
goodness of fit) ? Is it because i.segment works with the squared
distance and not the actual distance ?
IIUC, the worst goodness of fit measure (i.e. 1 - difference) is equal
to the 1 - threshold parameter value. This thus means that if one would
want to compare segmentations done with different threshold values by
comparing mean goodness of fit, for example, this would have to be
scaled taking into account the respective parameter value. Would
( goodness of fit - (1 - threshold parameter value) ) / threshold
make sense ?
BTW, in write_output.c, in the comments starting at line 82, there is
mention of a globals->threshold, but there is not threshold in the
globals structure... I guess this should read globals->alpha or
threshold->answer, or ?
More information about the grass-dev