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As already said in the title, I need some help with converting lat/long to x/y coords in Miller Cylindrical projection. I`m currently writing an app (in Java) which gets city list as an input and then gets lat/long for each city from Yahoo Placefinder. I used these formulas in my code. Here is an example of what I get. (image is for the reference only, not the one I use). As you can see the X positions are only a few pixels (2-3) off, this can be a problem with my calculations of prime meridian shift (CENTRAL_MERIDIAN_OFFSET) in this map. But the main problem is incorrect Y coordinates.

Here is my code (updated - 34px compensation for equator offset):

public final double W = 6343;
public final double H = 4767 - 34;

protected Point toMillerXY(double lon, double lat)
{
    double x, y;

    lon = Utils.degToRad(lon);
    lat = Utils.degToRad(lat);

    x = lon - CENTRAL_MERIDIAN_OFFSET;
    y = 1.25 * Math.log( Math.tan( 0.25 * Math.PI + 0.4 * lat ) );

    x = ( W / 2 ) + ( W / (2 * Math.PI) ) * x;
    y = ( H / 2 ) - ( H / ( 2 * 2.303412543 ) ) * y;

    y += 34;

    return new Point(x, y);
}

Output:  
Fetching data with: http://where.yahooapis.com/geocode?location=Buenos+Aires,Argentina
Latitude: -34.608521, longitude: -58.373539
---
Fetching data with: http://where.yahooapis.com/geocode?location=Tokyo,Japan
Latitude: 35.670479, longitude: 139.740921
---
Fetching data with: http://where.yahooapis.com/geocode?location=Cape+Town,CAR
Latitude: -33.919060, longitude: 18.421961
---
Fetching data with: http://where.yahooapis.com/geocode?location=Rome,Italy
Latitude: 41.903110, longitude: 12.495760
---
Total cities: 4
Result for Buenos Aires: 1964.598428, 3046.740995
Result for Tokyo: 5455.265150, 1732.669551
Result for Cape Town: 3317.692474, 3032.814395
Result for Rome: 3213.276105, 1602.176163

Obviously, something is wrong with Y coord calculation. I`m not sure whether 5.6 should really be the right value but the vertical range of Millers projection was said to be -2.3..+2.3 in one of the references I read so I used it.

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1 回答 1

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Millers projection was said to be -2.3..+2.3这是一个近似值。例如，根据图像的大小，您可能需要更精确的值2.303412543

对于莫斯科的纬度为 55.7522222，它将y = 1.089472895根据我使用的图像的高度给出 y' = 1499/2 - (1499/ (2 * 2.303412543)) * 1.089472895 = 395顶部的像素，这是正确的（我不关心 x）。

检查一下，我在地图上放了一个红点。 http://img7.imageshack.us/img7/9892/mapue.jpg

所以，可能你的图像中间没有赤道。它可以通过在公式中添加偏移来在数学上固定，但您必须找到赤道的位置。

于 2012-02-16T20:53:09.490 回答