设置世界风地图的缩放级别

Question

I am trying to setup a layer using worldwind java and i want to render icons on the map at their specific geo locations. I have that working but i want to be able to zoom to where all the icons are. Is there an easy way to do that? Im not really sure where to start.. Are there existing methods for zooming in on a group of points?

Answer 1

First you need to calculate the Sector containing all of your points. eg

Sector boundingSector = Sector.boundingSector(points);
//public static Sector boundingSector(Iterable<? extends LatLon> itrbl)

Now here's some code taken from ScankortDenmark example to calculate the zoom you need to fit the whole sector on screen:

// From ScankortDenmark example
public static double computeZoomForExtent(Sector sector)
{
    Angle delta = sector.getDeltaLat();
    if (sector.getDeltaLon().compareTo(delta) > 0)
        delta = sector.getDeltaLon();
    double arcLength = delta.radians * Earth.WGS84_EQUATORIAL_RADIUS;
    double fieldOfView = Configuration.getDoubleValue(AVKey.FOV, 45.0);
    return arcLength / (2 * Math.tan(fieldOfView / 2.0));
}

Answer 2

182Much's answer does work under under some conditions. However, a better solution must take into account that the Horizontal FOV (Field of View) is not always fixed at 45.0 degrees. It also needs to take into account the Vertical FOV. Even how the positions end of clustering has to be taken into account. Meaning, do the positions spread out more East to West or North and South. Is the users view of the globe (WorldWindow) actually skinnier then the height. All of these factors come into account when calculating the needed zoom level to view all positions. I created this static method to account for all of the listed positions above. As a side note, you can have slightly better precision if you calculate the actual mean radius of the Earth for where your positions tend to cluster instead of taken Earth.WGS84_EQUATORIAL_RADIUS. But this is almost negligible so I leave that part out here.

/**
 * Calculates the altitude in meters needed to view all of the given points.
 * This method is safe for any window sizing configurations. If the
 * WorldWindor arg is null then a static max altitude value of 1,0667,999
 * meters is returned. if the WorldWindow is good but the list of Positions
 * is null or empty then the current zoom level of the WorldWindow is
 * returned. If the list of positions cannot all be seen on the globe
 * because some positions are on the other side of the globe then a static
 * max altitude value of 1,0667,999 meters is returned.
 *
 * @param positions
 *            - a list of positions wanted to view
 * @return the altitude in meters needed to view all of the given points.
 */
public static double getZoomAltitude(List<Position> positions, WorldWindow wwd) {
    double zoom = 10667999;
    if (wwd != null) {
        // Gets the current zoom as a fail safe to return
        BasicOrbitView orbitView = (BasicOrbitView) wwd.getView();
        zoom = orbitView.getZoom();

        // zoom is in meters and and is limited the max zoom out to 10,667,999 meters
        int MAX_ZOOM = 10667999;

        if (positions != null && !positions.isEmpty()) {
            Sector sector = Sector.boundingSector(positions);
            if (sector != null) {

                // This calculation takes into account the window sizing configuration of the map in order to accurately 
                // display the list of positions.
                double meanRadius = Earth.WGS84_EQUATORIAL_RADIUS;

                // Next we must calculate the zoom levels for both delta latitude viewing and delta longitude viewing.
                // generally, a group of positions that spread out more Longitudenal viewing (wider viewing width) 
                // holds a constant 45.0 degree field of view (FOV). The horizontal FOV can be changed so this input 
                // must handle dynamically as well. The latitudenal (positon group runs more East to West then North and South) 
                // position group have a dynamic FOV that changes depending on the users sizing of the map. These have 
                // to be handled any time the group of positions has a greater delta latitude than delta longitude. 
                // Also if the user has a skinny map this will effect the output calculation and must be handled. 
                // Here we take all the dynamic variables into account for both types of possibilities and choose 
                // the larger zoom level of them. 
                int deltaLon = new BigDecimal(sector.getDeltaLon().radians * meanRadius).intValue();
                int deltaLat = new BigDecimal(sector.getDeltaLat().radians * meanRadius).intValue();
                System.out.println("deltaLonAL Wider: " + deltaLon + "\tdeltaLatAL Taller: " + deltaLat);

                double horizontalFOV = orbitView.getFieldOfView().getDegrees();
                double verticalFOV = ViewUtil.computeVerticalFieldOfView(orbitView.getFieldOfView(),
                        orbitView.getViewport()).getDegrees();

                double lonZoomLevel = new BigDecimal((deltaLon / 2.0) / (Math.tan(horizontalFOV / 2.0))).intValue();
                double latZoomLevel = new BigDecimal((deltaLat / 2.0)
                        / (Math.tan(Math.toRadians(verticalFOV) / 2.0))).intValue();
                System.out
                        .println("LonZoomLevel Wider: " + lonZoomLevel + "\tLatZoomLevel Taller: " + latZoomLevel);

                double zoomLevel = Math.max(lonZoomLevel, latZoomLevel);
                System.out.println("zoomLevel meters: " + zoomLevel + "\tfeet: "
                        + new BigDecimal(zoomLevel * 3.2808));

                // zoom is the altitude measured in meters to view a given area calculated to fit the viewing
                // window edge to edge. A buffer is needed around the area for visual appeal. The bufferedZoom
                // is a calculated linear equation (y = 1.0338x + 96177 where R² = 1) It gives the same buffer
                // boundary around a group of position depending on the calculated zoom altitude.
                double bufferedZoom = 1.0338 * zoomLevel + 96177;
                zoom = new BigDecimal(bufferedZoom).intValue();

                if (zoom > MAX_ZOOM) {
                    zoom = MAX_ZOOM;
                    System.out.println("MAX_ZOOM applied");
                }
            }
        } else {
            System.out.println("getZoomAltitude method cannot calculate the zoom because the points passed in was null and the current zoom was returned.");
        }
    }
    return zoom;
}