I want to give alternative interest points as input to SURF using the -p1 command (I'm using the authors implementation: http://www.vision.ee.ethz.ch/~surf/download.html). But I'm not sure what to make of the parameters.
I need to give x,y,a,b,c for each interest point, and according to the README, a=c and radius= 1/a^2 (with [a,b;b,c] being the entries of the second moment matrix). But when I look at an output file of surf's IP detection, the a,c parameter is always very small (e.g. 0.003). If radius=1/a^2, then that would give a region radius of 1/(0.003^2) > 100.000 pixels. Am I misinterpreting the README file, or are the a,c parameters that surf returns incorrect?
I think the README file is misleading. If you see the code. its actually a = 1/ radius^2. That puts the radius around 20 pixels in your example. go thru the main.cpp in the library to see how the a is calculated.