Conversion of latitude/longtitude into image coordinates (pixel coordinates)

You need the image dimension in pixels (width and height), a lat/lon reference point at a specified pixel position (e.g. lat0 and lon0 at x = y = 0), and the lat/lon degress covered by the image (e.g. by having another reference point at max. x and y).

First step is calculating the scaling factors in pixels per degree:

double scale_x = width / lon_range;
double scale_y = height / lat_range;

Now you can get the pixel positions:

double x = (lon - lon0) * scale_x;
double y = (lat - lat0) * scaly_y;

Finally convert them to integers with rounding:

int xp = static_cast<int>((x > 0) ? x + 0.5 : x - 0.5);
int yp = static_cast<int>((y > 0) ? y + 0.5 : y - 0.5);</int></int>

Note: This is just from scratch (had not tested it).