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Changed code to find a distance, useful for both in range and general distance.

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This commit is contained in:
AdenKoperczak 2024-07-07 13:14:01 -04:00
parent 1a37dbff27
commit b421251bcd
2 changed files with 122 additions and 103 deletions
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207
scwx-qt/source/scwx/qt/util/geographic_lib.cpp
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@ -31,6 +31,40 @@ const ::GeographicLib::Geodesic& DefaultGeodesic()
return geodesic_;
}
bool GnomonicAreaContainsCenter(geos::geom::CoordinateSequence sequence)
{
// Cannot have an area with just two points
if (sequence.size() <= 2 ||
(sequence.size() == 3 && sequence.front() == sequence.back()))
{
return false;
}
bool areaContainsPoint = false;
geos::geom::CoordinateXY zero {};
// If the sequence is not a ring, add the first point again for closure
if (!sequence.isRing())
{
sequence.add(sequence.front(), false);
}
// The sequence should be a ring at this point, but make sure
if (sequence.isRing())
{
try
{
areaContainsPoint =
geos::algorithm::PointLocation::isInRing(zero, &sequence);
}
catch (const std::exception&)
{
logger_->trace("Invalid area sequence");
}
}
return areaContainsPoint;
}
bool AreaContainsPoint(const std::vector<common::Coordinate>& area,
const common::Coordinate& point)
{
@ -146,60 +180,42 @@ GetDistance(double lat1, double lon1, double lat2, double lon2)
return units::length::meters<double> {distance};
}
bool AreaInRangeOfPoint(const std::vector<common::Coordinate>& area,
const common::Coordinate& point,
const units::length::meters<double> distance)
/*
* Uses the gnomonic projection to determine if the area is in the radius.
*
* The basic algorithm is as follows:
* - Get a gnomonic projection centered on the point of the area
* - Find the point on the area which is closest to the center
* - Convert the closest point back to latitude and longitude.
* - Find the distance form the closest point to the point.
*
* The first property needed to make this work is that great circles become
* lines in the projection, which allows the area to be converted to strait
* lines. This is generally true for gnomic projections.
*
* The second property needed to make this work is that a point further away
* on the geodesic must be further away on the projection. This means that
* the closes point on the projection is also the closest point on the geodesic.
* This holds for spherical geodesics and is an approximation non spherical
* geodesics.
*
* This algorithm only works if the area is fully on the hemisphere centered
* on the point. Otherwise, this falls back to centroid based distances.
*
* If the point is inside the area, 0 is always returned.
*/
units::length::meters<double>
GetDistanceAreaPoint(const std::vector<common::Coordinate>& area,
const common::Coordinate& point)
{
/*
Uses the gnomonic projection to determine if the area is in the radius.
The first property needed to make this work is that great circles become
lines in the projection.
The other key property needed to make this work is described bellow
R1 and R2 are the distances from the center point to two points
on the (non-flat) Earth.
R1' and R2' are the distances from the center point to the same
two points in the gnomonic projection.
if R1 > R2 then
R1' > R2'
else if R1 < R2 then
R1' < R2'
else if R1 == R2 then
R1' == R2'
This can also be written as:
r(d) is a function that takes the distance on Earth and converts it to a
distance on the projection.
R1' = r(R1), R2' = r(R2)
r(d) is increasing
In this case, R1 is a point the radius away from the center, and R2 is a
(all of the) point(s) on the edge of the area. This means that if the edge
is in the radius R1' on the projection, it is in the radius R1 on the Earth.
On a spherical geodesic this works fine. R is the radius of Earth. We are
also only concerned with points less than a hemisphere away, therefore
0 < R1,R2 < pi/2 * R (quarter of circumference because the point is in the
center of the hemisphere)
r(d) = R * tan(d / R) {0 < d < pi/2 * R}
tan(d / R) is increasing for {0 < d < pi/2 * R}
On non spherical geodesics, this may not work perfectly, but should be a
close approximation.
*/
// Cannot have an area with just two points
if (area.size() <= 2 || (area.size() == 3 && area.front() == area.back()))
{
return false;
}
// Ensure that the same geodesic is used here as is for the radius
// Ensure that the same geodesic is used here as is for the distance
// calculation
::GeographicLib::Gnomonic gnomonic =
::GeographicLib::Gnomonic(DefaultGeodesic());
geos::geom::CoordinateSequence sequence {};
double x;
double y;
bool useCentroid = false;
// Using a gnomonic projection with the test point as the center
// latitude/longitude, the projected test point will be at (0, 0)
@ -214,73 +230,64 @@ bool AreaInRangeOfPoint(const std::vector<common::Coordinate>& area,
areaCoordinate.longitude_,
x,
y);
// Check if the current point is the hemisphere centered on the point
// Check if the current point is in the hemisphere centered on the point
// if not, fall back to using centroid.
if (std::isnan(x) || std::isnan(y))
{
return false;
useCentroid = true;
}
sequence.add(x, y);
}
// get a point on the circle with the radius of the range in lat lon.
// Has the point be in the general direction of the area, which may help with
// non spherical geodesics
units::angle::degrees<double> angle = GetAngle(
point.latitude_, point.longitude_, area[0].latitude_, area[0].longitude_);
common::Coordinate radiusPoint = GetCoordinate(point, angle, distance);
// get the radius in gnomonic projection
gnomonic.Forward(point.latitude_,
point.longitude_,
radiusPoint.latitude_,
radiusPoint.longitude_,
x,
y);
// radius is greater than quarter circumference of the Earth, but the area
// is closer, so it is in range.
if (std::isnan(x) || std::isnan(y))
units::length::meters<double> distance;
if (useCentroid)
{
return true;
common::Coordinate centroid = common::GetCentroid(area);
distance = GetDistance(point.latitude_,
point.longitude_,
centroid.latitude_,
centroid.longitude_);
}
double gnomonicRadius = std::sqrt(x * x + y * y);
// If the sequence is not a ring, add the first point again for closure
if (!sequence.isRing())
else if (GnomonicAreaContainsCenter(sequence))
{
sequence.add(sequence.front(), false);
distance = units::length::meters<double>(0);
}
// The sequence should be a ring at this point, but make sure
if (sequence.isRing())
else
{
try
{
if (geos::algorithm::PointLocation::isInRing(zero, &sequence))
{
return true;
}
else if (distance > units::length::meters<double>(0))
{
// Calculate the distance the area is from the point via conversion
// to a polygon.
auto geometryFactory =
geos::geom::GeometryFactory::getDefaultInstance();
auto linearRing = geometryFactory->createLinearRing(sequence);
auto polygon =
geometryFactory->createPolygon(std::move(linearRing));
// Get the closes point on the geometry
auto geometryFactory = geos::geom::GeometryFactory::getDefaultInstance();
auto lineString = geometryFactory->createLineString(sequence);
geos::algorithm::distance::PointPairDistance distancePair;
geos::algorithm::distance::DistanceToPoint::computeDistance(
*polygon, zero, distancePair);
return gnomonicRadius >= distancePair.getDistance();
}
}
catch (const std::exception&)
{
logger_->trace("Invalid area sequence");
}
geos::algorithm::distance::PointPairDistance distancePair;
geos::algorithm::distance::DistanceToPoint::computeDistance(
*lineString, zero, distancePair);
geos::geom::CoordinateXY closestPoint = distancePair.getCoordinate(0);
double closestLat;
double closestLon;
gnomonic.Reverse(point.latitude_,
point.longitude_,
closestPoint.x,
closestPoint.y,
closestLat,
closestLon);
distance = GetDistance(point.latitude_,
point.longitude_,
closestLat,
closestLon);
}
return distance;
}
return false;
bool AreaInRangeOfPoint(const std::vector<common::Coordinate>& area,
const common::Coordinate& point,
const units::length::meters<double> distance)
{
return GetDistanceAreaPoint(area, point) <= distance;
}
} // namespace GeographicLib