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Units in the calculator
Christian Gass edited this page Jun 19, 2019
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- the input flow direction raster is introspected for the units of its CRS, which informs the selection of area and length conversion factors (since catchment area and flow length are derived directly from the flow direction raster):
- Conversion factors are explicitly passed into the geoprocessing functions: https://github.com/civicmapper/peak-flow-calculator/blob/39162ba1c3b77fe1c04af18f212c1092e7b84481/core/logic/__init__.py#L219
- Flow length is calculated and converted to meters https://github.com/civicmapper/peak-flow-calculator/blob/39162ba1c3b77fe1c04af18f212c1092e7b84481/core/logic/gp.py#L454
- Area is calculated and converted to square kilometers: https://github.com/civicmapper/peak-flow-calculator/blob/39162ba1c3b77fe1c04af18f212c1092e7b84481/core/logic/gp.py#L425
- All peak flow calculations are done with metric inputs and give back metric outputs (cubic meters/second). The original equations developed by the Cornell Soil & Water lab remain unchanged in that respect.
- All the results in the output table are (by default) converted to imperial units: https://github.com/civicmapper/peak-flow-calculator/blob/39162ba1c3b77fe1c04af18f212c1092e7b84481/core/logic/__init__.py#L283
- Flow length to feet
- Area to acres
- cubic meters / second to cubic feet / second