减去 2 个不同的双打结果为零

发布于 2024-10-26 06:53:00 字数 1124 浏览 1 评论 0原文

我正在构建一个基于 loc 的应用程序，使用 CLLocationManager 和 locationManager:didUpdateToLocation: fromLocation: 我正在尝试确定用户是否已移动到足以触发某些其他处理。我正在使用双变量。我很久以前就学会了不要将双精度数等同起来，而是将增量与阈值进行比较。我将绝对值（旧 - 新）与 0.0005f 的增量进行比较，

但是此代码...

    double latDelta = abs(theConsumer.latLong.clLocation.coordinate.latitude  - newLocation.coordinate.latitude);
    double lonDelta = abs(theConsumer.latLong.clLocation.coordinate.longitude - newLocation.coordinate.longitude);

    NSString *fooBar = [NSString stringWithFormat: 
           @"???Delta LAT: abs(current (%f) - new (%f)) = delta %f.",
           theConsumer.latLong.clLocation.coordinate.latitude,
           newLocation.coordinate.latitude,
           latDelta];

产生此输出：增量为零。

GPSLogger.m:(26)> GPSLOG：GPS：39.4425-北，77.8132-西/n MeterAccuracyFormat 0

GPSLogger.m：(26)> GPSLOG：找到新坐标：纬度：39.442494 经度：-77.813175 DataModel.m:(197)>距离地点：710.517020 DataModel.m:(199)>得到了 Delta > 0.000500 DataModel.m:(214)> Delta LAT：abs(当前 (39.440120) - 新 (39.442494)) = delta 0.000000。

数字已经满溢了吗？有没有更好的方法来做到这一点（即有效的方法）？

谢谢。

原文

I'm building a loc-based app, using CLLocationManager and locationManager:didUpdateToLocation: fromLocation:
I'm trying to determine if the user has moved enough to trigger some other processing.
I'm using double variables. I learned long ago not to equate doubles, but to compare the delta to a threshold. I compare the abs( old - new ) to a delta of 0.0005f

But this code...

    double latDelta = abs(theConsumer.latLong.clLocation.coordinate.latitude  - newLocation.coordinate.latitude);
    double lonDelta = abs(theConsumer.latLong.clLocation.coordinate.longitude - newLocation.coordinate.longitude);

    NSString *fooBar = [NSString stringWithFormat: 
           @"???Delta LAT: abs(current (%f) - new (%f)) = delta %f.",
           theConsumer.latLong.clLocation.coordinate.latitude,
           newLocation.coordinate.latitude,
           latDelta];

yields this output: delta is zero.

GPSLogger.m:(26)> GPSLOG: GPS: 39.4425- North, 77.8132- West/n MeterAccuracyFormat 0

GPSLogger.m:(26)> GPSLOG:New Coordinates found: Lat:39.442494 Lon:-77.813175
DataModel.m:(197)> DistanceFromLoc: 710.517020
DataModel.m:(199)> Got a delta > 0.000500
DataModel.m:(214)> Delta LAT: abs(current (39.440120) - new (39.442494)) = delta 0.000000.

Are the numbers overflowing? Is there a better way to do this (i.e. one that works)?

Thanks.

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