12 posts tagged with "java"

Background​

image reference¹

Considering that the Earth is neither flat nor a perfect sphere, but an irregular ellipsoid, there is no perfect formula for quickly and accurately calculating the distance between two points at different longitudes and latitudes.

However, by using the geotools library, you can obtain mathematically corrected approximations quite easily.

Adding Dependencies​

To use the Earth ellipsoid in geotools, you need to add the relevant library dependencies.

repositories {
    maven { url "https://repo.osgeo.org/repository/release/" }
    maven { url "https://download.osgeo.org/webdav/geotools/" }
    mavenCentral()
}

dependencies {
    ...
    implementation 'org.geotools:gt-referencing:26.2'
    ...
}

Writing Code​

First, define the coordinates of Seoul and Busan as an enum class.

enum class City(val latitude: Double, val longitude: Double) {
    SEOUL(37.5642135, 127.0016985),
    BUSAN(35.1104, 129.0431);
}

Next, let's look at a simple usage example through a test code.

class EllipsoidTest {

    @Test
    internal fun createEllipsoid() {
        val ellipsoid = DefaultEllipsoid.WGS84  // Creates an ellipsoid that is as close to the Earth as possible using the WGS84 geodetic system used in GPS

        val isSphere = ellipsoid.isSphere  // Determines if it is a sphere or an ellipsoid
        val semiMajorAxis = ellipsoid.semiMajorAxis  // Equatorial radius, the longer radius of the ellipsoid
        val semiMinorAxis = ellipsoid.semiMinorAxis  // Polar radius, the shorter radius of the ellipsoid
        val eccentricity = ellipsoid.eccentricity  // Eccentricity, indicates how close the ellipsoid is to a sphere
        val inverseFlattening = ellipsoid.inverseFlattening  // Inverse flattening value
        val ivfDefinitive = ellipsoid.isIvfDefinitive // Indicates if the inverse flattening is definitive for this ellipsoid

        // Orthodromic distance
        val orthodromicDistance = ellipsoid.orthodromicDistance(
            City.SEOUL.longitude,
            City.SEOUL.latitude,
            City.BUSAN.longitude,
            City.BUSAN.latitude
        )

        println("isSphere = $isSphere")
        println("semiMajorAxis = $semiMajorAxis")
        println("semiMinorAxis = $semiMinorAxis")
        println("eccentricity = $eccentricity")
        println("inverseFlattening = $inverseFlattening")
        println("ivfDefinitive = $ivfDefinitive")
        println("orthodromicDistance = $orthodromicDistance")
    }
}

isSphere = false
semiMajorAxis = 6378137.0
semiMinorAxis = 6356752.314245179
eccentricity = 0.08181919084262128
inverseFlattening = 298.257223563
ivfDefinitive = true
orthodromicDistance = 328199.9794919944

You can create an Earth ellipsoid with DefaultEllipsoid.WGS84. If you use SPHERE instead of WGS84, a sphere with a radius of 6371km will be created.

The distance result is in meters (m), so converting it to kilometers shows approximately 328km. If you search on Google, you may find 325km, so considering that there may be differences between the coordinates I chose and those chosen by Google, this is not a bad figure.

There are many other functions available as well. However, covering them all in this post would be too extensive, so if needed, I will cover them in another post.

Sometimes, the JSON naming conventions used in an API may differ from the naming strategy within your application.

{
  "Title": "Frozen",
  "Year": "2013",
  "Type": "movie",
  "Poster": "https://m.media-amazon.com/images/M/MV5BMTQ1MjQwMTE5OF5BMl5BanBnXkFtZTgwNjk3MTcyMDE@._V1_SX300.jpg",
  "imdbID": "tt2294629"
}

private String title;
private String year;
private String imdbId;
private String type;
private String poster;

If the variable names do not match the JSON keys, the data will not be populated.

In such cases, you can use @JsonProperty(value) to map the data without changing the variable names in the project. However, if there are many fields with different naming strategies, using @JsonProperty(value) on each field can clutter the code with too many annotations.

This is where the @JsonNaming annotation comes in handy, allowing you to change the naming strategy of a class at once.

@JsonNaming​

Before v2.12​

You can elegantly solve this as follows:

@Data
@JsonNaming(value = PropertyNamingStrategy.UpperCamelCaseStrategy.class)
public class Movie {

    private String title;
    private String year;

    @JsonProperty("imdbID")  // Only where needed!
    private String imdbId;
    private String type;
    private String poster;

}

This method is deprecated and marked with a strikethrough.

However, this method has been deprecated since Jackson 2.12, so let's explore the newer approach.

After v2.12​

Starting from version 2.12, you should use PropertyNamingStrategies.

@JsonNaming(value = PropertyNamingStrategies.UpperCamelCaseStrategy.class)

While a detailed explanation of the internal implementation may be too lengthy and off-topic, it is recommended to take a look as it is quite interestingly implemented!