bandpass filter: shape dependency of frequency response
In gsg_generate_tm_bpf (and equivalently in the port pygsg.filter._generate_bpf_legacy), the data (x
, y
; say frequency space and bandpass function) that is used for the radial interpolation onto nd-arrays of different size (i.e., template and tile) is generated given a dimension n
. The space x
is then generated as x = [0:n]/n
, i.e., scaled to [0:1]
. The bandpass function y
however is agnostic to this scaling of the underlying space. As a consequence, the interpolated filter will have an effective action depending on n
and the filter parameters don't have a global interpretation but only a local interpretation with respect to the shape used to 1d-data creation. In the current implementation this n
is the size of the first dimension of the template. Thus the filter parameters must be interpreted with respect to the template and have a different meaning with respect to the tile.
Just to be clear: the issue is not that the interpolated filters are having different effects on the tile and the template but that the filter parameters don't have the geometrical interpretation (in terms of lengths and scales) that their names suggest!