为什么getSpeed​​（）总是在Android返回0 [英] why getSpeed() always return 0 on android

问题描述

我需要的速度和GPS方位。然而，只有一些我从 location.getSpeed​​（） 0或有时不可用。我的code：

I need to get the speed and heading from the gps. However the only number i have from location.getSpeed() is 0 or sometimes not available. my code:

        String provider = initLocManager();
    if (provider == null)
        return false;
    LocationListener locListener = new LocationListener() {
        public void onLocationChanged(Location location) {
            updateWithNewLocation(location, interval, startId);
            Log.i(getString(R.string.logging_tag), "speed =" + location.getSpeed());
        }

        public void onProviderDisabled(String provider){
            updateWithNewLocation(null, interval, startId);
        }

        public void onProviderEnabled(String provider) {}
        public void onStatusChanged(String provider, int status, Bundle extras) {}
    };

    _locManager.requestLocationUpdates(provider, interval,  DEFAULT_GPS_MIN_DISTANCE, locListener);


    private String initLocManager() {
    String context = Context.LOCATION_SERVICE;
    _locManager = (LocationManager) getSystemService(context);

    Criteria criteria = new Criteria();
    criteria.setAccuracy(Criteria.ACCURACY_FINE);
    criteria.setAltitudeRequired(false);
    criteria.setBearingRequired(true);
    criteria.setSpeedRequired(true);
    criteria.setCostAllowed(true);
    //criteria.setPowerRequirement(Criteria.POWER_LOW);
    String provider = _locManager.getBestProvider(criteria, true);

    if (provider == null || provider.equals("")) {
        displayGPSNotEnabledWarning(this);
        return null;
    }

    return provider;
}

我试着打与标准，但没有成功。有没有人有一个想法是什么问题？

I tried to play the Criteria with but no success. Does anyone have an idea what is the problem?

推荐答案

location.getSpeed​​（）只返回了什么设置location.setSpeed​​（）。这是一个值，你可以为某个位置对象设置。

location.getSpeed() only returns what was set with location.setSpeed(). This is a value that you can set for a location object.

要计算使用GPS的速度，你就必须做一些数学：

To calculate the speed using GPS, you'll have to do a little math:

Speed = distance / time

所以，你需要做的：

So you would need to do:

(currentGPSPoint - lastGPSPoint) / (time between GPS points)

全部转换为英尺/秒，或者不管你要显示的速度。这是我做的，当我做了一个亚军的应用程序。

All converted to ft/sec, or however you want to show the speed. This is how I did it when I made a runner app.

更具体地讲，你需要计算绝对距离：

More specifically, you'll need to calculate for absolute distances:

(sqrt((currentGPSPointX - lastGPSPointX)^2) + (currentGPSPointY - lastGPSPointY)^2)) / (time between GPS points)

这可能有助于使一个新的TrackPoint类或什么的，这使它被带到里面的GPS位置和时间。

It might help to make a new TrackPoint class or something, which keeps the GPS location and time it was taken inside.

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