On Feb 7, 4:59 pm, Martin Matysiak <[email protected]> wrote:
> I'm not absolutely sure if I've understood your problem, so here's what I
> think you want to do:
>
> You have an marker-icon that is shifted some pixels (!) away from the actual
> location you want to point at. When the user clicks on the marker, a line
> from your anchor to the actual location shall be drawn. Is this correct?
>
> If this would be the case, I have implemented the following method:
>
> /*
> * Calculates the Latitude/Longitude per
> * Pixel ratio based on the given zoom.
> *
> * If you want to speed up things, you might
> * replace the formula by an array of constant
> * LatLng values, as the ratio isn't depending
> * on any factors but the map's scaling. If
> * This should change in the future, you would have
> * to adjust the formula either way.
> *
> * @param zoom The zoom value for which you want
> * to know the conversion ratio from
> * pixel to LatLng
> */
> function getLatLngPerPixel(zoom) {
> var lng = 360 / (256 * (Math.pow(2,zoom))); //256 is the Map Width
> (px) on zoom = 0
> var lat = 2 * lng / Math.PI;
>
> return new google.maps.LatLng(lat, lng);
>
> }
>
> This method gives you the "size" of a pixel in Latitude/Longitude
> coordinates for a specific map zoom (by the way, you could also fill this
> method with a static array containing the precalculated values for each
> zoom). Now if you want to draw a line from your location to the anchor, just
> get the conversion ratio, take your location as point A of the line, then
> calculate point B of the line by multiplying your x/y values with the
> corresponding conversion ratio and adding this to the coordinates of your
> point A.
Unfortunately, LngToX & XToLng are linear but LatToY & YToLat are non
linear. Using a constant multiplier for the vertical component will
not work. It is the reason Google has to chop flat images into
horizontal slices to force a Euclidian projection to look like a
Mercator projection. At very deep zoom levels, you may not notice it.
Several different versions of the conversion functions are floating
around. See:
http://www.polylib.us/adjust.js
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