Geoscience Reference
In-Depth Information
10.1.1 Interpolation Methods
invdist
Inverse distance to a power. This is the default algorithm for interpolating the
points within the search ellipse. The resulting value
z
is a weighted average of
the values
z
i
of all
n
points that are found within the ellipse. The weights
w
are
calculated as the inverse distance
r
i
from these points to the center of the grid
cell, raised to the power
p
. The default value of
power
is two. Increasing this
value will decrease the contribution of more distant points. Setting a positive
value for (
smoothing
) will result in smoother results as it will add this value
to the calculated distance.
i
=
1
w
i
z
i
w
i
1
r
p
z
=
,
with
w
i
=
i
,
(10.1)
where
z
and
z
i
are the values of the target grid cell and the i-th point within the
search ellipse respectively.
average
Moving average algorithm. This is a simplified form of the weighting average
(invdist), where the weights are all equal to one (or power equals to 0). Each
point within the search ellipse has the same contribution to the resulting grid cell
value, regardless of its distance to the grid cell center. Do not forget to set the
radii of the search ellipse to a positive value. When left at their default value of
zero, all grid cells will obtain an identical value, equal to the average of all points
in the input vector file.
nearest
Nearest neighbor algorithm. The grid cell will obtain the value of the nearest
point in the input vector file. The point must be within the search ellipse when
both radii are set. Otherwise it obtains a no-data value.
10.1.2 Data Metrics
The
gdal_grid
utility supports a number of metrics that can be calculated for
the points in the input vector file. The metrics provide information on the points
that are found within the search ellipse of each grid cell (node). This can be:
the minimum/maximum of these points, their range (max-min), their count and
some distance measure.
minimum
Minimum value found in grid node search ellipse.
maximum
Maximum value found in grid node search ellipse.
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