Negative values in impedance datasets

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In the main.py, for therecalc_impedance command, out_nodata is defined as -9999. According to Graphab v3.0 data requirements, the negative and 0 values are not allowed in any impedance datasets. No data value should be also strictly > 0 (not zero):

https://thema.univ-fcomte.fr/flarum/d/47-negative-or-null-cost-is-forbiddencheck-your-cost

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If Data4Land is used for follow-up processing in Graphab, values of input and enriched LULC do not need to be > 0.
Therefore, No Data value for these datasets can be defined negative or 0.