SIFT density image function and filter

From OTBWiki

The idea here is to code an image function (similar to the variance image function, for instance) which computes the number of SIFT/per pixel detected in the neighborhood of a given pixel in a scalar image. This function can afterwards be used in a filter in order to produce an image of densities.

The SIFT image function can be seen as a particular case where a detector (producing points, lines etc., that is vector data) + a count method (simple count, count + condition on the detected objects, density -- count/nb pixels) are combined to produce meaningful information:

CountImageFunction< DetectorType, CountStrategy, ConditionOnObject=AlwaysTrue>

ConditionOnObject is for instance a functor which returns a boolean value after operating on single detections produced by the DetectorType. CountStrategy can be SimpleCount, PerPixelDensity, etc.