and make it compatible with OTB7 and OTB 8

This musn't be reset everytime we enter an thread!!

WIP: because we still need to use geoid file even if $OTB_GEOID_FILE isn't set

Resolve "Add -mean option to ExtractNormalVector"

Closes #6

See merge request !5

Resolve "Automatically inject NODATA metadata in generated images"

Closes #4

See merge request !3

Merge branch '4-automatically-inject-nodata-metadata-in-generated-images' of gitlab.orfeo-toolbox.org:s1-tiling/normlim_sigma0 into 4-automatically-inject-nodata-metadata-in-generated-images

Resolve "Adapt DiapOTB SARCartesianMeanEstimation to keep shadows"

Closes #2

See merge request !1

Use a mean on valid all low, high, left and right points, instead of only one
point each time.

TODO: Add an option to let us choose: one psingle point or mean

The conversion to int16 will be done after orthorectofication

However the output mask receives a 2 instead of 0 (nodata), or 1 (nominally
computed)

by commenting out logs

And check most likelly invalid states first ({0,0,0} is more likelly to happen
than nan's)

Avoid float -> double -> float conversions: works on floats all the way down

The dichotomic search doesn't assign a correct value to "last" end-bound when
it's close the end of image line

- no monotonic progression
- ascendant monotonic progression
- descendant monotonic progression

Instead of iterating over all DEM lines again and again, a dichotomic search is
done as long as we know DEM lines progression is monotonic to the exploration.

TODO:

- test the case where lines are sorted in ascending order
- support the case where there is no monotonic progression

and improve class interface:

- remove dependency to `std::iterator` deprecated in C++17
- use class traits internally
- add comparison operators

Future algorithms will need to directly access the underlying data. ITK
iterators will be an hindrance and as such they will be reaplced with iterators
compatibles with C++ standard algorithms

Replace out-parameters with returned values

- cache `m_member_variables`
- cache origin value
- cache low and hi margins as the internal input pixel type (likelly `float`)
  in order to avoid operations between `float` and `double`
- replace `while` with `for` where iterating...

micro optim:
- memorize `m_member_variables`,
- move invariants out of loop,
- remove branch