Getting pixel coordinated from google static maps

Question

I want to find out the pixels coordinates of a lat/lng on an static map. For example i've downloaded an image from:

Link to Image

What I want is from a lat/lng long to be able to map that latlng to pixel coordinates. I've searched a bit and found that mercator projection can solve my problem. However I could not find any proper way of doing it. Can somebody please help me. Also I've zoomed to 9 when as shown in the URL.

Answer 1

Converting Lat/Lon to pixel for a google static map is very useful if you want to draw on the map's bitmap directly. This can be a better approach than passing hundreds of parameters with the URL. I had the same problem and found four solutions in the web which looked very similar but where written in other languages. I translated it into C#. I am sure it will be easy to use this simple code also in Java or C:

//(half of the earth circumference's in pixels at zoom level 21)
static double offset = 268435456; 
static double radius = offset / Math.PI;
// X,Y ... location in degrees
// xcenter,ycenter ... center of the map in degrees (same value as in 
// the google static maps URL)
// zoomlevel (same value as in the google static maps URL)
// xr, yr and the returned Point ... position of X,Y in pixels relativ 
// to the center of the bitmap
static Point Adjust(double X, double Y, double xcenter, double ycenter, 
                    int zoomlevel)
{
    int xr = (LToX(X) - LToX(xcenter)) >> (21 - zoomlevel);
    int yr = (LToY(Y) - LToY(ycenter)) >> (21 - zoomlevel);
    Point p = new Point(xr, yr);
    return p;
}

static int LToX(double x)
{
    return (int)(Math.Round(offset + radius * x * Math.PI / 180));
}

static int LToY(double y)
{
    return (int)(Math.Round(offset - radius * Math.Log((1 + 
                 Math.Sin(y * Math.PI / 180)) / (1 - Math.Sin(y * 
                 Math.PI / 180))) / 2));
}

Usage:

1. call this function to get the X and Y pixel coordinates
2. the result is referenced to the center of the bitmap, so add the bitmaps width/2 and heigth/2 to the x and y value. This gives you the absolute pixel position
3. check if the pixel position is inside your bitmap
4. draw whatever you want

It does not work close to the poles because of Google's variant of Mercator projection, but for the usual coordinates it works very well.

Answer 2

harry4616's code in python:

import math
OFFSET = 268435456 # half of the earth circumference's in pixels at zoom level 21
RADIUS = OFFSET / math.pi

def get_pixel(x, y, x_center, y_center, zoom_level):
    """
    x, y - location in degrees
    x_center, y_center - center of the map in degrees (same value as in the google static maps URL)
    zoom_level - same value as in the google static maps URL
    x_ret, y_ret - position of x, y in pixels relative to the center of the bitmap
    """
    x_ret = (l_to_x(x) - l_to_x(x_center)) >> (21 - zoom_level)
    y_ret = (l_to_y(y) - l_to_y(y_center)) >> (21 - zoom_level)
    return x_ret, y_ret

def l_to_x(x):
    return int(round(OFFSET + RADIUS * x * math.pi / 180))

def l_to_y(y):
    return int(round(OFFSET - RADIUS * math.log((1 + math.sin(y * math.pi / 180)) / (1 - math.sin(y * math.pi / 180))) / 2))