ex06_missing_values
This example extends the missing-value configuration from merge2d ex07 into
three dimensions. The primary model has value 8 and occupies 15/85 along x,
y, and z. It stores a rectangular missing block as its declared NetCDF fill
value. This block is internal in x-y but touches the lower z boundary. The
secondary model has value 2, covers the full 0/100 cube, and uses the
undeclared sentinel -99999 for a perpendicular block that touches the west
x boundary but is internal along z.
At z = 50 km, the primary and secondary gaps reproduce the vertical and
horizontal bands from the two-dimensional example. Their z extents make the
same missing-value relationships visible in a vertical section along
y = 50 km.
The mergefile is:
primary.nc?vp secondary.nc?p - - cosine/cosine/cosine 0.25
secondary.nc?p - - - - -
The symmetric cosine taper operates at both ends of x, y, and z. GMT’s common
input option -di-99999 converts the undeclared secondary sentinel to NaN.
Without internal-gap interpolation, merge3d retains the available model
where only one member is missing and returns NaN where both are missing.
The merging weight depends only on the primary support and is not altered by
data availability.
The -Hl option fills the primary’s internal x-y holes with linear Delaunay
interpolation. The secondary gap is connected to an x-y boundary and is
therefore preserved by -H, but -Sl+g bridges its internal missing z layers.
Together, the options fill both orthogonal gaps before merging:
gmt merge3d missing.merge3d -R0/100/0/100 -I1 -T0/100/1 \
-Fvp -di-99999 -Hl -Sl+g -W -nl -Gfilled.nc
Panels (a-e) show horizontal slices at z = 50 km; panels (f-j) show vertical
sections along y = 50 km. Blue outlines mark the primary gap, orange outlines
mark the secondary gap, and the dashed black line marks the vertical-section
location. The primary support is outlined in the input and weight panels.
Run:
./ex06_missing_values.sh
The script checks primary-only, secondary-only, and jointly missing samples in
both views. After horizontal and vertical interpolation, it verifies the
complete result against merged = 2 + 6 * weight. It creates
ex06_missing_values.png and ex06_missing_values.pdf.
Figures
