22 lines
1.1 KiB
GLSL
22 lines
1.1 KiB
GLSL
/**
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* Computes the fraction of a Web Wercator rectangle at which a given geodetic latitude is located.
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*
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* @name czm_latitudeToWebMercatorFraction
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* @glslFunction
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*
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* @param {float} latitude The geodetic latitude, in radians.
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* @param {float} southMercatorY The Web Mercator coordinate of the southern boundary of the rectangle.
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* @param {float} oneOverMercatorHeight The total height of the rectangle in Web Mercator coordinates.
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*
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* @returns {float} The fraction of the rectangle at which the latitude occurs. If the latitude is the southern
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* boundary of the rectangle, the return value will be zero. If it is the northern boundary, the return
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* value will be 1.0. Latitudes in between are mapped according to the Web Mercator projection.
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*/
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float czm_latitudeToWebMercatorFraction(float latitude, float southMercatorY, float oneOverMercatorHeight)
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{
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float sinLatitude = sin(latitude);
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float mercatorY = 0.5 * log((1.0 + sinLatitude) / (1.0 - sinLatitude));
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return (mercatorY - southMercatorY) * oneOverMercatorHeight;
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}
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