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added comments and improved code layout

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This commit is contained in:
AdenKoperczak 2024-07-01 16:16:54 -04:00
parent 9f47e0ad72
commit 2bc971eb94
2 changed files with 73 additions and 20 deletions
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91
scwx-qt/source/scwx/qt/util/geographic_lib.cpp
View file

@ -14,7 +14,8 @@ namespace scwx
{
namespace qt
{
namespace util {
namespace util
{
namespace GeographicLib
{
@ -149,15 +150,52 @@ 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 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;
}
::GeographicLib::Gnomonic gnomonic =
// Ensure that the same geodesic is used here as is for the radius
// calculation
::GeographicLib::Gnomonic gnomonic =
::GeographicLib::Gnomonic(DefaultGeodesic());
geos::geom::CoordinateSequence sequence {};
double x;
@ -176,11 +214,19 @@ bool AreaInRangeOfPoint(const std::vector<common::Coordinate>& area,
areaCoordinate.longitude_,
x,
y);
// Check if the current point is the hemisphere centered on the point
if (std::isnan(x) || std::isnan(y))
{
return false;
}
sequence.add(x, y);
}
// get a point on the circle with the radius of the range in lat lon.
units::angle::degrees<double> angle = units::angle::degrees<double>(0);
// 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_,
@ -189,7 +235,13 @@ bool AreaInRangeOfPoint(const std::vector<common::Coordinate>& area,
radiusPoint.longitude_,
x,
y);
double gnomonicRadius = sqrt(x * x + y * 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))
{
return true;
}
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())
@ -206,22 +258,21 @@ bool AreaInRangeOfPoint(const std::vector<common::Coordinate>& area,
{
return true;
}
// Calculate the distance the point is from the output
geos::algorithm::distance::PointPairDistance distancePair;
auto geometryFactory =
geos::geom::GeometryFactory::getDefaultInstance();
auto linearRing = geometryFactory->createLinearRing(sequence);
auto polygon =
geometryFactory->createPolygon(std::move(linearRing));
geos::algorithm::distance::DistanceToPoint::computeDistance(*polygon,
zero,
distancePair);
if (gnomonicRadius > distancePair.getDistance())
else if (distance > units::length::meters<double>(0))
{
return true;
}
// 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));
geos::algorithm::distance::PointPairDistance distancePair;
geos::algorithm::distance::DistanceToPoint::computeDistance(
*polygon, zero, distancePair);
return gnomonicRadius >= distancePair.getDistance();
}
}
catch (const std::exception&)
{

2
scwx-qt/source/scwx/qt/util/geographic_lib.hpp
View file

@ -96,6 +96,8 @@ GetDistance(double lat1, double lon1, double lat2, double lon2);
* distance of a point. A point lying on the area boundary is considered to be
* inside the area, and thus always in range. Any part of the area being inside
* the radius counts as inside.
* This is limited to having the area be in the same hemisphere centered on
* the point, and radices up to a quarter of the circumference of the Earth.
*
* @param [in] area A vector of Coordinates representing the area
* @param [in] point The point to check against the area