|
Gri Commands
1: Introduction 2: Simple example 3: Fancy example 4: Running Gri 5: Programming Gri 6: General Issues 7: X-Y Plots 8: Contour Plots 9: Image Plots 10: Examples 11: Handling Data 12: Gri Commands 13: Gri Extras 14: Evolution of Gri 15: Installing Gri 16: Gri Bugs 17: System Tools 18: Acknowledgments 19: License 20: Newsgroup 21: Concept Index |
12.44: The `
All these smoothing commands ignore the location of the data. For
equispaced data these algorithms have the standard interpretation in
terms of digital filters. For non-equispaced data, the interpretation
is up to the user.
|
`smooth {x [.n.]} \
| {y [.n.]} \
| {grid data [.f.|{along x|y}]}'
|
smooth x' command does smoothing by the following formula
x[i-1] x[i] x[i+1] ------ + ---- + ------ 4 2 4 |
smooth x .n.' command does boxcar smoothing using centred
boxcars `.n.' points wide.
The `smooth y' command does the same as `smooth x', but on the
`y' column.
There are several methods of smoothing grid data. Note that isolated
missing values are filled in by each method. (Let the author know if
you'd like that `feature' to be an option.)
The `smooth grid data' command smooths gridded data, by weighted
average in a plus-shaped window about each gridpoint. The smoothing
algorithm replaces each interior gridpoint value `z[i][j]' by
z[i][j] z[i-1][j] + z[i+1][j] + z[i][j-1] + z[i][j+1] ------- + --------------------------------------------- 2 8 |
smooth grid data .f.' command performs partial smoothing. A
temporary fully-smoothed grid `zSMOOTH[i][h]' is constructed as
above, and a linear combination of this grid and the original grid is
used as the replacement grid:
z[i][j] = (1-f) * z[i][j] + f * zSMOOTH[i][j] |
f' is the value indicated on the command line.
Thus, `smooth grid data 0' performs no smoothing at all, while
`smooth grid data 1' is equivalent to `smooth grid data'.
The `smooth grid data along x' command smooths the grid data
across `x' (i.e., horizontally), by replacing each value
`z[i][j]' with the value
z[i][j] z[i-1][j] + z[i+1][j] ------- + --------------------- 2 4 |
smooth grid data along y' command does the same thing as
`smooth grid data along x', but the smoothing is along `y'.
See also see Filter, a generalization of `smooth x|y'
which allows for more sophisticated filters.
