NetCDF Variable Selection

Selectors

Select NetCDF fields by appending ? and a comma-separated list to the NetCDF filename:

model.nc?vp,vs,rho

Use quotations for selectors containing shell-sensitive square brackets or parentheses. If ? is omitted, the module uses its documented default field-selection behavior. Input modifiers follow the selected field list, for example model.nc?vp,vs+x0.001+Xkm+v0.001,0.001+Vkm/s,km/s scales an input axis in metres to kilometres and the selected fields from m/s to km/s. A selector containing only modifiers, such as model.nc?+x0.001+Xkm, applies them to the default field without naming it. An undeclared numeric missing sentinel may be defined with +n.

Positional mapping

The merge modules map selected variables by position, so source names may be different when they represent equivalent quantities. For exammple, given:

model1.nc?vp,vs,den
model2.nc?p,s,d

the option -Fvp,vs,rho writes both triples as vp, vs, and rho. Every source record must list equivalent variables in the same order. -F names output variables. It does not select variables from an input file.

A single explicit selector retains its source name when -F is omitted. When neither a selector nor -F supplies a name and one default field is used, the merge output variable is named z.

Input selector modifiers are applied before interpolation and merging. The merge modules use -Z for transforms applied to the completed output. A single field scale or unit is broadcast. Otherwise, values follow -F order when -F is supplied and selector order otherwise. -Z scales output coordinates and fields in place and does not reorder coordinates, fields, or weights. See Scaling and Units for the full processing order and modifier meanings.

Selecting a 3-D layer in merge2d

Use a zero-based index in square brackets:

gmt merge2d 'model.nc?vs[3]' ...

Use parentheses to select the layer nearest a coordinate value without vertical interpolation:

gmt merge2d 'model.nc?vs(20)' ...

For multiple variables, give one layer selector per field. Source coordinate scaling is applied before coordinate-value selection, so (20) is interpreted in the transformed/scaled source coordinate system.

Property mappings

elygtl uses explicit semantic mappings such as -Fvp=p,vs=s,rho=density because its calculations rely on seismic wavespeed properties. At least Vp or Vs must be mapped. -C names properties to create when they are entirely absent from the model.