Scaling and Units

Processing order

GQ decodes NetCDF scale_factor and add_offset packing and sets missing values before applying user-specified transforms. Numerical source transforms therefore operate on unpacked values. Geometry selection, interpolation, support polygon tests, and merging use the transformed coordinates and fields.

Input transforms

Lowercase modifiers apply numerical scales to an input source:

• +x, +y, and +z scale coordinate axes.

• +v scales selected field values.

Uppercase +X, +Y, +Z, and +V assign target-unit metadata to the corresponding transformed values. A single field scale or unit is broadcast. Otherwise lists follow selector or -F order.

For example, a source with negative-down depth in metres can use +z-0.001+Zkm to produce an increasing positive-down coordinate in kilometres. In the merge, topobath, elygtl, and SSH modules, input coordinate scaling does not reorder coordinates or associated data. Every transformed input axis must instead be strictly increasing. Use a negative input scale when it makes a decreasing source axis increase, and use output -Z to restore a coordinate convention of your choosing.

For example, +z-1/1000+Zkm converts a source z axis stored as 4000 ... -16000 m to -4 ... 16 km in the same sample order. After merging, -Z+z-1000+Zm restores the original decreasing convention without reordering any data. Thus, parameters defined at -4 km are still the same at 4000 m.

Output transforms

The merge, topobath, elygtl, and SSH modules provide -Z for output coordinate and field transforms. The lowercase modifiers scale output values, while uppercase modifiers set their unit metadata. Field scales and units are positional for multiparameter output. -Z scales output coordinates and fields in place and does not reorder coordinates, fields, or weights. A negative axis scale therefore writes that coordinate in decreasing order.

In topobath, field scales and units follow the selected model-field order. Its coordinate modifiers also transform the optional -Q diagnostic grids, but classification codes cannot be scaled. Please consult the usage at Modules for the complete accepted syntax in each module.

For SSH application, source scaling occurs before gap filling and resampling, so correlation lengths and maximum vertical gap spans are interpreted in the transformed working units. -Z follows heterogeneity generation, tapering, and model application. Field scales and units follow -F ordering.

Topobath convention

topobath applies source scaling first and then works in the resulting vertical convention. The transformed model z coordinate must increase from top to bottom, with negative elevations above sea level and positive depths below it. Transformed old and new topography values must use the same signs. Use a model +z scale and a surface +v or +z scale to standardize inputs before -T<zmin>/<zmax>/<dz> is interpreted. -Z is a final output transform for x, y, z, and selected model fields. A negative axis scale may restore a preferred convention without reordering coordinates or model layers.

Ely GTL units

elygtl calculates in metres, seconds, m/s, and kg/m3. Input transforms standardize stored data before the module’s unit conversion.