Geografic-Information-System/imagery/i.atcorr

Adding new band filters (see also Iwave.h):

Note: the spectral range is from 250 nm to 4000 nm (see Iwave.h) which is
4000-250=3750nm. The step size is (4000-250)/1500=2.5 nm in the ffu.s array.

o bands are defined by their discrete filter function
o to compute a band position in the 1500 slots of ffu.s array, start
with 250nm using 2.5nm increments. The result is the starting index
for the spectral band.
o 1500 is the number of wavelength spectral description slots.
- a 'for' loop fills up the slots with 0
- then the ffu.s array is filled with each of the spectral band data
one after the other.
Example Lsat TM: (435-250) / 2.5 = 74

o add filter function to Iwave.cpp, before IWave::equivwl()
o add else-if in IWave::parse() in Iwave.cpp
o add print strings in Iwave.cpp

o add iwave values and signature in Iwave.h
o add to GeomCond.cpp and GeomCond.h
o add to i.atcorr.html


Preparation of the Iwave.cpp file code:

The helper script create_iwave.py can help to interpolate the filter functions
to the correct step size of 2.5 nm (in case that the filter function data
are delivered with a different step size).
The output filter function in a format as needed in the Iwave.cpp file.

The script create_iwave.py basically needs a .csv file with spectral
response for each band in a column. The first column has to be the
wavelength (nm). The first line (and only first) is a header with
wavelength, followed by band names file name is used for sensor name.
See for example ./sensors_csv/ikonos.csv.

Usage
create_iwave.py

If generates the filter function as IWave.cpp template from csv file.

Note: If the spectral response is null for a frequency, leave it empty
in csv file. Ex.:

WL(nm),band 1,band 2,band 3,band 4
455,0.93,,,
485,0.94,0.00,,
545,0.00,0.87,0.00,

Program will interpolate filter function to 2.5 nm steps
and output a CPP template file in the IWave format.