Google Earth API - drawing lines that curve?

问题:

I've been playing with the google earth API. I thought it would be neat to draw some lines between places from a relative 3D viewpoint. I've searched through the GE documentation and searched on google for answers but didn't find anything that led me down the correct path, so I thought I'd post some code and perhaps get some insight.

The following code plots two places and then draws a line between those places. Unfortunately the line that gets drawn splices the earth. Is there a method to make it wrap to the contour of the earth when drawn in 3D like this? I've attempted to vary the line height placement with a varying degree of success, but at the cost of accuracy and overall visual appeal when the line doesn't appear to connect the places.

function init() {
    google.earth.createInstance('map3d', initCB, failureCB);
}

function initCB(instance) {
    ge = instance;
    ge.getWindow().setVisibility(true);


    //---------------------------------PLACES   

    // Create the placemark.
    var placemark = ge.createPlacemark('');
    placemark.setName("Location 1");

    // Set the placemark's location.  
    var point = ge.createPoint('');
    point.setLatitude(39.96028);
    point.setLongitude(-82.979736);
    placemark.setGeometry(point);

    // Add the placemark to Earth.
    ge.getFeatures().appendChild(placemark);


    // Create the placemark.
    var placemark2 = ge.createPlacemark('');
    placemark2.setName("Hop #2");

    // Set the placemark's location.  
    var point2 = ge.createPoint('');
    point2.setLatitude(25.7615);
    point2.setLongitude(-80.2939);
    placemark2.setGeometry(point2);

    // Add the placemark to Earth.
    ge.getFeatures().appendChild(placemark2);

    //---------------------------------FOCUS

    var lookAt = ge.createLookAt('');
    lookAt.setLatitude(39.96028);
    lookAt.setLongitude(-82.979736);
    lookAt.setRange(1000000.0);
    lookAt.setAltitude(0);
    lookAt.setTilt(45);
    ge.getView().setAbstractView(lookAt);


    //---------------------------------LINES

    // Create the placemark
    var lineStringPlacemark = ge.createPlacemark('');

    // Create the LineString
    var lineString = ge.createLineString('');
    lineStringPlacemark.setGeometry(lineString);

    // Add LineString points
    lineString.getCoordinates().pushLatLngAlt(39.96028, -82.979736, 0);
    lineString.getCoordinates().pushLatLngAlt(25.7615, -80.2939, 0);
    //lineString.setAltitudeMode(ge.ALTITUDE_CLAMP_TO_GROUND);
    //lineString.setAltitudeMode(ge.ALTITUDE_RELATIVE_TO_GROUND);
    lineString.setAltitudeMode(ge.absolute);

    // Create a style and set width and color of line
    lineStringPlacemark.setStyleSelector(ge.createStyle(''));
    var lineStyle = lineStringPlacemark.getStyleSelector().getLineStyle();
    lineStyle.setWidth(2);
    lineStyle.getColor().set('9900ffff');  // aabbggrr format

    // Add the feature to Earth
    ge.getFeatures().appendChild(lineStringPlacemark);

}

function failureCB(errorCode) {
}

google.setOnLoadCallback(init);

回答1:

You will want to set tesselation, and optionally extrude, on your linestring to true.

See https://developers.google.com/kml/documentation/kmlreference#tessellate and https://developers.google.com/kml/documentation/kmlreference#extrude for details

For the API, your syntax would be something like

lineStringPlacemark.setTessellate(true);
lineStringPlacemark.setExtrude(true);

There's some additional API examples on this at https://developers.google.com/earth/documentation/geometries