All Known Implementing Classes:

Healpix
```
public interface Projection
```
Define a projection of spherical coordinates (in the unit sphere) to the Euclidean plane, together with the reverse operation. Remark: we use arrays instead of objects because HEALPix is a low level library focused on performances. Accessing an element in an array is faster than accessing a class attribute.

Author:

F.-X. Pineau

Field Summary

Fields
Modifier and Type	Field	Description
`static int`	`LAT_INDEX`	Index of the lattitude in the array containing the result of an unproject method.
`static int`	`LON_INDEX`	Index of the longitude in the array containing the result of an unproject method.
`static int`	`X_INDEX`	Index of the x coordinate in the array containing the result of a project method.
`static int`	`Y_INDEX`	Index of the y coordinate in the array containing the result of a project method.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`double[]`	`project(double lonRad, double latRad)`	Project the given spherical coordinates into the Euclidean plane.
`void`	`project(double lonRad, double latRad, double[] resultXY)`	See `project(double, double)` with the result stored in the given array.
`double[]`	`unproject(double x, double y)`	Reverse projection: we look for spherical coordinates from their projected coordinates (`project(double, double)`.
`void`	`unproject(double x, double y, double[] resultLonLat)`	See `unproject(double, double)` with the result stored in the given array.

- Field Detail
  - LON_INDEX
```
static final int LON_INDEX
```
    Index of the longitude in the array containing the result of an unproject method.
    
    See Also:
    
    Constant Field Values
  - LAT_INDEX
```
static final int LAT_INDEX
```
    Index of the lattitude in the array containing the result of an unproject method.
    
    See Also:
    
    Constant Field Values
  - X_INDEX
```
static final int X_INDEX
```
    Index of the x coordinate in the array containing the result of a project method.
    
    See Also:
    
    Constant Field Values
  - Y_INDEX
```
static final int Y_INDEX
```
    Index of the y coordinate in the array containing the result of a project method.
    
    See Also:
    
    Constant Field Values
- Method Detail
  - project
```
double[] project(double lonRad,
                 double latRad)
```
    Project the given spherical coordinates into the Euclidean plane.
    
    Parameters:
    
    lonRad - longitude in radians (the accepted value range is implementation dependent)
    
    latRad - latitude in [-pi/2, pi/2] radians
    
    Returns:
    
    the projection of the given spherical coordinate into the Euclidean plane. The x and y coordinate are stored in the returned array at indices X_INDEX and Y_INDEX respectively. The range of possible value for x and y is implementation dependent.
  - project
```
void project(double lonRad,
             double latRad,
             double[] resultXY)
```
    See project(double, double) with the result stored in the given array.
    
    Parameters:
    
    lonRad - see project(double, double)
    
    latRad - see project(double, double)
    
    resultXY - array used to store the result. Must be of size >= 2.
  - unproject
```
double[] unproject(double x,
                   double y)
```
    Reverse projection: we look for spherical coordinates from their projected coordinates (project(double, double).
    
    Parameters:
    
    x - the x coordinate of the projected spherical point we are looking for, the accepted value range is implementation dependent
    
    y - the y coordinate of the projected spherical point we are looking for, must be in [-2, 2].
    
    Returns:
    
    the spherical coordinates leading to the given projection coordinates. The lon and lat coordinate are stored in the returned array at indices LON_INDEX and LAT_INDEX respectively. Lat is in [-pi/2, pi/2] radians, lon is also in radians but it possible value range is implementation dependent).
  - unproject
```
void unproject(double x,
               double y,
               double[] resultLonLat)
```
    See unproject(double, double) with the result stored in the given array.
    
    Parameters:
    
    x - unproject(double, double)
    
    y - unproject(double, double)
    
    resultLonLat - array used to store the result. Must be of size >= 2.

Interface Projection

Field Summary

Method Summary

Field Detail

LON_INDEX

LAT_INDEX

X_INDEX

Y_INDEX

Method Detail

project

project

unproject

unproject