+ xpad = width * scale - xsize
+ ypad = height * scale - ysize
+
+ @width = width
+ @height = height
+
+ @tx = xsheet(min_lon) - xpad / 2
+ @ty = ysheet(min_lat) - ypad / 2
+
+ @bx = xsheet(max_lon) + xpad / 2
+ @by = ysheet(max_lat) + ypad / 2
+ end
+
+ #the following two functions will give you the x/y on the entire sheet
+
+ def ysheet(lat)
+ log(tan(PI / 4 + (lat * PI / 180 / 2))) / (PI / 180)
+ end
+
+ def xsheet(lon)
+ lon
+ end
+
+ #and these two will give you the right points on your image. all the constants can be reduced to speed things up. FIXME
+
+ def y(lat)
+ return @height - ((ysheet(lat) - @ty) / (@by - @ty) * @height)