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desruisseaux pushed a commit to branch geoapi-4.0
in repository https://gitbox.apache.org/repos/asf/sis.git
The following commit(s) were added to refs/heads/geoapi-4.0 by this push:
new 8a7a5d8 Add comment explaining better how the scale factors are
computed in `GridDerivation.subgrid(…)`.
8a7a5d8 is described below
commit 8a7a5d8d1aee453d88acefa317cb70b03fd39fc5
Author: Martin Desruisseaux <[email protected]>
AuthorDate: Tue Apr 9 14:46:23 2019 +0200
Add comment explaining better how the scale factors are computed in
`GridDerivation.subgrid(…)`.
---
.../main/java/org/apache/sis/coverage/grid/GridDerivation.java | 8 ++++++++
.../src/main/java/org/apache/sis/coverage/grid/GridGeometry.java | 5 +++++
2 files changed, 13 insertions(+)
diff --git
a/core/sis-raster/src/main/java/org/apache/sis/coverage/grid/GridDerivation.java
b/core/sis-raster/src/main/java/org/apache/sis/coverage/grid/GridDerivation.java
index b5f62e0..4db9d15 100644
---
a/core/sis-raster/src/main/java/org/apache/sis/coverage/grid/GridDerivation.java
+++
b/core/sis-raster/src/main/java/org/apache/sis/coverage/grid/GridDerivation.java
@@ -412,6 +412,14 @@ public class GridDerivation {
if (baseExtent != base.extent &&
baseExtent.equals(gridOfInterest.extent)) {
baseExtent = gridOfInterest.extent;
// Share common instance.
}
+ /*
+ * The subsampling will be determined by scale factors of the
transform from the given desired grid geometry to
+ * the current (base) grid geometry. For example a scale of 10
means that every time we advance by one pixel in
+ * `gridOfInterest`, we will advance by 10 pixels in `base`. We
compute the scales (indirectly, because of the
+ * way transforms are concatenated) as the ratio between
`gridOfInterest` resolution and `base` resolution,
+ * computed in the center of the area of interest (may be
different than base grid center). In the following
+ * call to `resolution(…)`, the domain must be the source of the
`mapCenters` transform.
+ */
scales = GridGeometry.resolution(mapCenters, domain);
}
return this;
diff --git
a/core/sis-raster/src/main/java/org/apache/sis/coverage/grid/GridGeometry.java
b/core/sis-raster/src/main/java/org/apache/sis/coverage/grid/GridGeometry.java
index 1009186..2b86fce 100644
---
a/core/sis-raster/src/main/java/org/apache/sis/coverage/grid/GridGeometry.java
+++
b/core/sis-raster/src/main/java/org/apache/sis/coverage/grid/GridGeometry.java
@@ -762,6 +762,10 @@ public class GridGeometry implements Serializable {
*
* <p>Note that for this computation, it does not matter if {@code
gridToCRS} is the user-specified
* transform or the {@code this.gridToCRS} field value; both should
produce equivalent results.</p>
+ *
+ * @param gridToCRS a transform for which to compute the resolution, or
{@code null} if none.
+ * @param domain the domain for which to get a resolution, or {@code
null} if none.
+ * If non-null, must be the source of {@code gridToCRS}.
*/
static double[] resolution(final MathTransform gridToCRS, final GridExtent
domain) {
final Matrix matrix = MathTransforms.getMatrix(gridToCRS);
@@ -778,6 +782,7 @@ public class GridGeometry implements Serializable {
/**
* Computes the resolutions from the given matrix. This is the magnitude
of each row vector.
*
+ * @param gridToCRS Jacobian matrix or affine transform for which to
compute the resolution.
* @param numToIgnore number of rows and columns to ignore at the end of
the matrix.
* This is 0 if the matrix is a derivative (i.e. we ignore
nothing), or 1 if the matrix
* is an affine transform (i.e. we ignore the translation column
and the [0 0 … 1] row).
