ImageFormat: Document units/coordinate system for DEPTH_POINT_CLOUD

For camera devices, DEPTH_POINT_CLOUD coordinates are in meters and
are in the camera's local coordinate system.

Test: Built docs, manually verified output.
Bug: 67308479
Change-Id: I028e13a2fb79688a7ce440f905fa82826fc38a03

graphics/java/android/graphics/ImageFormat.java

@@ -658,6 +658,14 @@ public class ImageFormat {
      *    float confidence = floatDepthBuffer.get();
      * </pre>
      *
+     * For camera devices that support the
+     * {@link android.hardware.camera2.CameraCharacteristics#REQUEST_AVAILABLE_CAPABILITIES_DEPTH_OUTPUT DEPTH_OUTPUT}
+     * capability, DEPTH_POINT_CLOUD coordinates have units of meters, and the coordinate system is
+     * defined by the camera's pose transforms:
+     * {@link android.hardware.camera2.CameraCharacteristics#LENS_POSE_TRANSLATION} and
+     * {@link android.hardware.camera2.CameraCharacteristics#LENS_POSE_ROTATION}. That means the origin is
+     * the optical center of the camera device, and the positive Z axis points along the camera's optical axis,
+     * toward the scene.
      */
     public static final int DEPTH_POINT_CLOUD = 0x101;