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Correct mercator projection. Use epsg naming

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Alexander Nozik 2022-09-10 18:04:42 +03:00
parent 42e0a4c46d
commit 25e9eed88d
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3 changed files with 60 additions and 26 deletions
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6
maps-kt-compose/src/jvmMain/kotlin/center/sciprog/maps/compose/MapViewJvm.kt
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@ -251,7 +251,11 @@ public actual fun MapView(
val bottomRight = feature.oval.bottomRight.toOffset()
val path = Path().apply {
addArcRad(Rect(topLeft, bottomRight), feature.startAngle, feature.endAngle - feature.startAngle)
addArcRad(
Rect(topLeft, bottomRight),
feature.startAngle.radians.value.toFloat(),
(feature.endAngle - feature.startAngle).radians.value.toFloat()
)
}
drawPath(path, color = feature.color, style = Stroke())

60
maps-kt-core/src/commonMain/kotlin/center/sciprog/maps/coordinates/MercatorProjection.kt
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@ -6,45 +6,46 @@
package center.sciprog.maps.coordinates
import center.sciprog.maps.coordinates.Angle.Companion.pi
import kotlin.math.atan
import kotlin.math.ln
import kotlin.math.sinh
import kotlin.math.*
public data class ProjectionCoordinates(val x: Distance, val y: Distance)
/**
* @param T the type of projection coordinates
*/
public interface MapProjection<T: Any>{
public interface MapProjection<T : Any> {
public fun toGeodetic(pc: T): GeodeticMapCoordinates
public fun toProjection(gmc: GeodeticMapCoordinates): T
public companion object{
public val epsg3857: MercatorProjection = MercatorProjection()
}
}
/**
* @param baseLongitude the longitude offset in radians
* @param radius the average radius of the Earth
* @param correctedRadius optional radius correction to account for ellipsoid model
* @param ellipsoid - a [GeoEllipsoid] to be used for conversion
*/
public open class MercatorProjection(
public val baseLongitude: Angle = Angle.zero,
protected val radius: Distance = DEFAULT_EARTH_RADIUS,
private val correctedRadius: ((GeodeticMapCoordinates) -> Distance)? = null,
): MapProjection<ProjectionCoordinates> {
public val ellipsoid: GeoEllipsoid = GeoEllipsoid.sphere,
) : MapProjection<ProjectionCoordinates> {
override fun toGeodetic(pc: ProjectionCoordinates): GeodeticMapCoordinates {
val res = GeodeticMapCoordinates.ofRadians(
atan(sinh(pc.y / radius)),
baseLongitude.radians.value + (pc.x / radius),
atan(sinh(pc.y / ellipsoid.equatorRadius)),
baseLongitude.radians.value + (pc.x / ellipsoid.equatorRadius),
)
return if (correctedRadius != null) {
val r = correctedRadius.invoke(res)
GeodeticMapCoordinates.ofRadians(
atan(sinh(pc.y / r)),
baseLongitude.radians.value + pc.x / r,
)
} else {
return if (ellipsoid === GeoEllipsoid.sphere) {
res
} else {
TODO("Elliptical mercator projection not implemented")
// GeodeticMapCoordinates(
// atan(sinh(pc.y / ellipsoid.polarRadius)).radians,
// res.longitude,
// )
}
}
@ -53,15 +54,26 @@ public open class MercatorProjection(
*/
override fun toProjection(gmc: GeodeticMapCoordinates): ProjectionCoordinates {
require(abs(gmc.latitude) <= MAXIMUM_LATITUDE) { "Latitude exceeds the maximum latitude for mercator coordinates" }
val r: Distance = correctedRadius?.invoke(gmc) ?: radius
return ProjectionCoordinates(
x = r * (gmc.longitude - baseLongitude).radians.value,
y = r * ln(tan(pi / 4 + gmc.latitude / 2))
val e = sqrt(ellipsoid.eSquared)
return if (ellipsoid === GeoEllipsoid.sphere) {
ProjectionCoordinates(
x = ellipsoid.equatorRadius * (gmc.longitude - baseLongitude).radians.value,
y = ellipsoid.equatorRadius * ln(tan(pi / 4 + gmc.latitude / 2))
)
} else {
val sinPhi = sin(gmc.latitude)
ProjectionCoordinates(
x = ellipsoid.equatorRadius * (gmc.longitude - baseLongitude).radians.value,
y = ellipsoid.equatorRadius * ln(
tan(pi / 4 + gmc.latitude / 2) * ((1 - e * sinPhi) / (1 + e * sinPhi)).pow(e / 2)
)
)
}
public companion object : MercatorProjection(Angle.zero, Distance(6378.137)) {
}
public companion object {
public val MAXIMUM_LATITUDE: Angle = 85.05113.degrees
public val DEFAULT_EARTH_RADIUS: Distance = radius
}
}

18
maps-kt-core/src/commonTest/kotlin/center/sciprog/maps/coordinates/MercatorTest.kt Normal file
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@ -0,0 +1,18 @@
package center.sciprog.maps.coordinates
import kotlin.test.Test
import kotlin.test.assertEquals
class MercatorTest {
@Test
fun forwardBackward(){
val moscow = Gmc.ofDegrees(55.76058287719673, 37.60358622841869)
val mercator = MapProjection.epsg3857.toProjection(moscow)
//https://epsg.io/transform#s_srs=4326&t_srs=3857&x=37.6035862&y=55.7605829
assertEquals(4186.0120709, mercator.x.kilometers, 1e-4)
assertEquals(7510.9013658, mercator.y.kilometers, 1e-4)
val backwards = MapProjection.epsg3857.toGeodetic(mercator)
assertEquals(moscow.latitude.degrees.value, backwards.latitude.degrees.value, 0.001)
assertEquals(moscow.longitude.degrees.value, backwards.longitude.degrees.value, 0.001)
}
}