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Issue #1279 add some comments to the grid wrap chaecking code.

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Former-commit-id: a78273a16f [formerly cd1af813dc843102784b82fe452e6150de021375]
Former-commit-id: 632bd9e051
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Ben Steffensmeier 2012-10-19 13:49:48 -05:00
parent 53d1dce044
commit 9c9bb42707
1 changed files with 27 additions and 0 deletions
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27
edexOsgi/com.raytheon.uf.common.geospatial/src/com/raytheon/uf/common/geospatial/interpolation/data/AbstractDataWrapper.java
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@ -130,18 +130,45 @@ public abstract class AbstractDataWrapper implements DataSource,
.getGridToCRS(PixelInCell.CELL_CENTER);
MathTransform crs2LatLon = CRS.findMathTransform(sourceCRS,
DefaultGeographicCRS.WGS84);
// Although theoretically any two points would yield the same
// result, nx is chosen as the x coordinate because it overcomes
// some of the normalization performed in geotools math transforms.
// For most math transforms, geotools will normalize the LatLon
// values into into the range centralMeridian +/- 180. In these
// cases the 360 degree shift performed later is completely
// worthless since geotools will normalize the points into the
// same range regardless of how it is shifted. For a worldwide grid
// the nx coordinate is guaranteed to be just slightly over the
// normalized range, so that when the transform normalizes it will
// use a point that is -360 degrees away from the original point.
// This means that even though the -360 degree shift we apply is
// worthless, the normalization process actually applies an
// equivelant shift that yields the correct result. The end result
// is that whether the transform normalizes or not there is always a
// shift of -360 degrees for all worldwide grids.
// Start with two points in grid space, one on each corner side of
// the y direction.
DirectPosition2D corner1 = new DirectPosition2D(nx, 0);
DirectPosition2D corner2 = new DirectPosition2D(nx, ny - 1);
// transform the points to crs space.
grid2crs.transform(corner1, corner1);
grid2crs.transform(corner2, corner2);
// and then to latLon space
crs2LatLon.transform(corner1, corner1);
crs2LatLon.transform(corner2, corner2);
// shift the points by 360 degrees because the goal is to know how
// many grid cells exist in one 360 roll of longitude.
corner1.x = corner1.x - 360;
corner2.x = corner2.x - 360;
// transform back to crs.
crs2LatLon.inverse().transform(corner1, corner1);
crs2LatLon.inverse().transform(corner2, corner2);
// and back to grid space
grid2crs.inverse().transform(corner1, corner1);
grid2crs.inverse().transform(corner2, corner2);
// the difference between the starting x value and the current x
// value is the number
int sourceWrapX = (int) (nx - corner1.x);
// In order to wrap then the transformed point x value should be
// on the other side of the grid and the y value should not have