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Apache Lucene (module: spatial3d)
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.lucene.spatial3d.geom;
/**
* An object for accumulating latitude/longitude bounds information.
*
* @lucene.experimental
*/
public class LatLonBounds implements Bounds {
/** Set to true if no longitude bounds can be stated */
private boolean noLongitudeBound = false;
/** Set to true if no top latitude bound can be stated */
private boolean noTopLatitudeBound = false;
/** Set to true if no bottom latitude bound can be stated */
private boolean noBottomLatitudeBound = false;
/** If non-null, the minimum latitude bound */
private Double minLatitude = null;
/** If non-null, the maximum latitude bound */
private Double maxLatitude = null;
// For longitude bounds, this class needs to worry about keeping track of the distinction
// between left-side bounds and right-side bounds. Points are always submitted in pairs
// which have a maximum longitude separation of Math.PI. It's therefore always possible
// to determine which point represents a left bound, and which point represents a right
// bound.
//
// The next problem is how to compare two of the same kind of bound, e.g. two left bounds.
// We need to keep track of the leftmost longitude of the shape, but since this is a circle,
// this is arbitrary. What we could try to do instead would be to find a pair of (left,right) bounds such
// that:
// (1) all other bounds are within, and
// (2) the left minus right distance is minimized
// Unfortunately, there are still shapes that cannot be summarized in this way correctly.
// For example. consider a spiral that entirely circles the globe; we might arbitrarily choose
// lat/lon bounds that do not in fact circle the globe.
//
// One way to handle the longitude issue correctly is therefore to stipulate that we
// walk the bounds of the shape in some kind of connected order. Each point or circle is therefore
// added in a sequence. We also need an interior point to make sure we have the right
// choice of longitude bounds. But even with this, we still can't always choose whether the actual shape
// goes right or left.
//
// We can make the specification truly general by submitting the following in order:
// addSide(PlaneSide side, Membership... constraints)
// ...
// This is unambiguous, but I still can't see yet how this would help compute the bounds. The plane
// solution would in general seem to boil down to the same logic that relies on points along the path
// to define the shape boundaries. I guess the one thing that you do know for a bounded edge is that
// the endpoints are actually connected. But it is not clear whether relationship helps in any way.
//
// In any case, if we specify shapes by a sequence of planes, we should stipulate that multiple sequences
// are allowed, provided they progressively tile an area of the sphere that is connected and sequential.
// For example, paths do alternating rectangles and circles, in sequence. Each sequence member is
// described by a sequence of planes. I think it would also be reasonable to insist that the first segment
// of a shape overlap or adjoin the previous shape.
//
// Here's a way to think about it that might help: Traversing every edge should grow the longitude bounds
// in the direction of the traversal. So if the traversal is always known to be less than PI in total longitude
// angle, then it is possible to use the endpoints to determine the unambiguous extension of the envelope.
// For example, say you are currently at longitude -0.5. The next point is at longitude PI-0.1. You could say
// that the difference in longitude going one way around would be beter than the distance the other way
// around, and therefore the longitude envelope should be extended accordingly. But in practice, when an
// edge goes near a pole and may be inclined as well, the longer longitude change might be the right path, even
// if the arc length is short. So this too doesn't work.
//
// Given we have a hard time making an exact match, here's the current proposal. The proposal is a
// heuristic, based on the idea that most areas are small compared to the circumference of the globe.
// We keep track of the last point we saw, and take each point as it arrives, and compute its longitude.
// Then, we have a choice as to which way to expand the envelope: we can expand by going to the left or
// to the right. We choose the direction with the least longitude difference. (If we aren't sure,
// and can recognize that, we can set "unconstrained in longitude".)
/** If non-null, the left longitude bound */
private Double leftLongitude = null;
/** If non-null, the right longitude bound */
private Double rightLongitude = null;
/** Construct an empty bounds object */
public LatLonBounds() {
}
// Accessor methods
/** Get maximum latitude, if any.
*@return maximum latitude or null.
*/
public Double getMaxLatitude() {
return maxLatitude;
}
/** Get minimum latitude, if any.
*@return minimum latitude or null.
*/
public Double getMinLatitude() {
return minLatitude;
}
/** Get left longitude, if any.
*@return left longitude, or null.
*/
public Double getLeftLongitude() {
return leftLongitude;
}
/** Get right longitude, if any.
*@return right longitude, or null.
*/
public Double getRightLongitude() {
return rightLongitude;
}
// Degenerate case check
/** Check if there's no longitude bound.
*@return true if no longitude bound.
*/
public boolean checkNoLongitudeBound() {
return noLongitudeBound;
}
/** Check if there's no top latitude bound.
*@return true if no top latitude bound.
*/
public boolean checkNoTopLatitudeBound() {
return noTopLatitudeBound;
}
/** Check if there's no bottom latitude bound.
*@return true if no bottom latitude bound.
*/
public boolean checkNoBottomLatitudeBound() {
return noBottomLatitudeBound;
}
// Modification methods
@Override
public Bounds addPlane(final PlanetModel planetModel, final Plane plane, final Membership... bounds) {
plane.recordBounds(planetModel, this, bounds);
return this;
}
@Override
public Bounds addHorizontalPlane(final PlanetModel planetModel,
final double latitude,
final Plane horizontalPlane,
final Membership... bounds) {
if (!noTopLatitudeBound || !noBottomLatitudeBound) {
addLatitudeBound(latitude);
}
return this;
}
@Override
public Bounds addVerticalPlane(final PlanetModel planetModel,
final double longitude,
final Plane verticalPlane,
final Membership... bounds) {
if (!noLongitudeBound) {
addLongitudeBound(longitude);
}
return this;
}
@Override
public Bounds isWide() {
return noLongitudeBound();
}
@Override
public Bounds addXValue(final GeoPoint point) {
if (!noLongitudeBound) {
// Get a longitude value
addLongitudeBound(point.getLongitude());
}
return this;
}
@Override
public Bounds addYValue(final GeoPoint point) {
if (!noLongitudeBound) {
// Get a longitude value
addLongitudeBound(point.getLongitude());
}
return this;
}
@Override
public Bounds addZValue(final GeoPoint point) {
if (!noTopLatitudeBound || !noBottomLatitudeBound) {
// Compute a latitude value
double latitude = point.getLatitude();
addLatitudeBound(latitude);
}
return this;
}
@Override
public Bounds addIntersection(final PlanetModel planetModel, final Plane plane1, final Plane plane2, final Membership... bounds) {
plane1.recordBounds(planetModel, this, plane2, bounds);
return this;
}
@Override
public Bounds addPoint(GeoPoint point) {
if (!noLongitudeBound) {
// Get a longitude value
addLongitudeBound(point.getLongitude());
}
if (!noTopLatitudeBound || !noBottomLatitudeBound) {
// Compute a latitude value
addLatitudeBound(point.getLatitude());
}
return this;
}
@Override
public Bounds noLongitudeBound() {
noLongitudeBound = true;
leftLongitude = null;
rightLongitude = null;
return this;
}
@Override
public Bounds noTopLatitudeBound() {
noTopLatitudeBound = true;
maxLatitude = null;
return this;
}
@Override
public Bounds noBottomLatitudeBound() {
noBottomLatitudeBound = true;
minLatitude = null;
return this;
}
@Override
public Bounds noBound(final PlanetModel planetModel) {
return noLongitudeBound().noTopLatitudeBound().noBottomLatitudeBound();
}
// Protected methods
/** Update latitude bound.
*@param latitude is the latitude.
*/
private void addLatitudeBound(double latitude) {
if (!noTopLatitudeBound && (maxLatitude == null || latitude > maxLatitude))
maxLatitude = latitude;
if (!noBottomLatitudeBound && (minLatitude == null || latitude < minLatitude))
minLatitude = latitude;
}
/** Update longitude bound.
*@param longitude is the new longitude value.
*/
private void addLongitudeBound(double longitude) {
// If this point is within the current bounds, we're done; otherwise
// expand one side or the other.
if (leftLongitude == null && rightLongitude == null) {
leftLongitude = longitude;
rightLongitude = longitude;
} else {
// Compute whether we're to the right of the left value. But the left value may be greater than
// the right value.
double currentLeftLongitude = leftLongitude;
double currentRightLongitude = rightLongitude;
if (currentRightLongitude < currentLeftLongitude)
currentRightLongitude += 2.0 * Math.PI;
// We have a range to look at that's going in the right way.
// Now, do the same trick with the computed longitude.
if (longitude < currentLeftLongitude)
longitude += 2.0 * Math.PI;
if (longitude < currentLeftLongitude || longitude > currentRightLongitude) {
// Outside of current bounds. Consider carefully how we'll expand.
double leftExtensionAmt;
double rightExtensionAmt;
if (longitude < currentLeftLongitude) {
leftExtensionAmt = currentLeftLongitude - longitude;
} else {
leftExtensionAmt = currentLeftLongitude + 2.0 * Math.PI - longitude;
}
if (longitude > currentRightLongitude) {
rightExtensionAmt = longitude - currentRightLongitude;
} else {
rightExtensionAmt = longitude + 2.0 * Math.PI - currentRightLongitude;
}
if (leftExtensionAmt < rightExtensionAmt) {
currentLeftLongitude = leftLongitude - leftExtensionAmt;
while (currentLeftLongitude <= -Math.PI) {
currentLeftLongitude += 2.0 * Math.PI;
}
leftLongitude = currentLeftLongitude;
} else {
currentRightLongitude = rightLongitude + rightExtensionAmt;
while (currentRightLongitude > Math.PI) {
currentRightLongitude -= 2.0 * Math.PI;
}
rightLongitude = currentRightLongitude;
}
}
}
double testRightLongitude = rightLongitude;
if (testRightLongitude < leftLongitude)
testRightLongitude += Math.PI * 2.0;
if (testRightLongitude - leftLongitude >= Math.PI) {
noLongitudeBound = true;
leftLongitude = null;
rightLongitude = null;
}
}
}