This module discusses the control parameters for:
-
- Negative values
-
- Vertical orientation
-
- Duplicate
input coordinates
The control parameter non determines
whether negative values are allowed as interpolated values. The default
is to allow them. If disallowed, by setting the value of the control
parameter
non to
1, then any value that would otherwise be negative
is set to zero.
The plots in
Example 5 illustrate this.
Compare the
plot that allows negative values with the
plot that does not allow them.
This feature is useful if you have a function, such a pressure,
that should never have a negative value.
The control parameter
upd determines the ordering
of the second dimension of the output array. The default,
"upd = 1", implies a south to north ordering;
setting upd to 0 reverses the order.
The control parameter
dup determines whether
duplicate input coordinates are allowed. By default they
are not allowed, the assumption being that such points might
represent a flaw in the input data. If duplicate input
coordinates are allowed and different data values are assigned for
these points,
these values will be interpreted as different data values that
are very closely spaced, since Natgrid adds a small random perturbation to
each input coordinate so that all input coordinates are unique.
See
Dave Watson's book, nngridr, for details on this.
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