将小数纬度/经度坐标转换为iPad屏幕坐标 [英] Convert decimal latitude/longitude coordinates to iPad screen coordinates

问题描述

我有一个纬度/经度小数点坐标，我想将其转换为适合iPad坐标系区域的点。

I have a latitude/longitude decimal coordinates that I would like to convert to points that will fit within the area of the iPad coordinate system.

我的代码采用纬度/经度坐标并将它们转换为笛卡尔坐标（基于这个问题：转换为笛卡尔坐标）转换结果为（2494.269287,575.376465）。

My code takes in a latitude/longitude coordinates and converts them to cartesian coordinates (based on this question: convert to cartesian coordinates) The results of the conversion are (2494.269287, 575.376465).

这是我的代码（没有编译或运行时错误）：

Here is my code (no compile or runtime errors):

#define EARTH_RADIUS 6371

- (void)drawRect:(CGRect)rect
{
    CGPoint latLong = {41.998035, -116.012215};

    CGPoint newCoord = [self convertLatLongCoord:latLong];

    NSLog(@"Cartesian Coordinate: (%f, %f)",newCoord.x, newCoord.y);

    //Draw dot at coordinate
    CGColorRef darkColor = [[UIColor colorWithRed:21.0/255.0
                                            green:92.0/255.0
                                             blue:136.0/255.0
                                            alpha:1.0] CGColor];
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, darkColor);
    CGContextFillRect(context, CGRectMake(newCoord.x, newCoord.y, 100, 100));

}

-(CGPoint)convertLatLongCoord:(CGPoint)latLong
{
    CGFloat x = EARTH_RADIUS * cos(latLong.x) * cos(latLong.y);
    CGFloat y = EARTH_RADIUS * cos(latLong.x) * sin(latLong.y);

    return CGPointMake(x, y);
}

如何将小数点坐标转换为将显示在iPad上的坐标屏幕？

How can I convert the decimal coordinates to coordinates that will show up on an iPad screen?

推荐答案

您的 convertLatLongCoord：方法不会尝试调整结果指向屏幕坐标。如上所述，您可以在 -EARTH_RADIUS x 和 y 值c $ c>到 + EARTH_RADIUS 。这些需要缩放以适应屏幕。

Your convertLatLongCoord: method makes no attempt to adjust the resulting point to screen coordinates. As written, you can get x and y values in the range -EARTH_RADIUS to +EARTH_RADIUS. These need to be scaled to fit the screen.

以下内容应该有所帮助：

Something like the following should help:

- (CGPoint)convertLatLongCoord:(CGPoint)latLong {
    CGFloat x = EARTH_RADIUS * cos(latLong.x) * cos(latLong.y) * SCALE + OFFSET;
    CGFloat y = EARTH_RADIUS * cos(latLong.x) * sin(latLong.y) * SCALE + OFFSET;

    return CGPointMake(x, y);
}

SCALE 和 OFFSET 应该是一个确定如下的值：

SCALE and OFFSET should be a value determined as follows:

CGSize screenSize = [UIScreen mainScreen].applicationFrame.size;
CGFloat SCALE = MIN(screenSize.width, screenSize.height) / (2.0 * EARTH_RADIUS);
CGFloat OFFSET = MIN(screenSize.width, screenSize.height) / 2.0;

这假设您希望地图填充最小的屏幕尺寸。

This assumes you want the map to fill the smallest screen dimension.

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