; docformat = 'rst' ; ; NAME: ; cgGoogle_MetersPerPixel ; ; PURPOSE: ; ; This funtion returns the number of meters per pixel for a particular zoom level ; in images returned using Google's Static Image API. ;******************************************************************************************; ; ; ; Copyright (c) 2012, by Fanning Software Consulting, Inc. All rights reserved. ; ; ; ; Redistribution and use in source and binary forms, with or without ; ; modification, are permitted provided that the following conditions are met: ; ; ; ; * Redistributions of source code must retain the above copyright ; ; notice, this list of conditions and the following disclaimer. ; ; * Redistributions in binary form must reproduce the above copyright ; ; notice, this list of conditions and the following disclaimer in the ; ; documentation and/or other materials provided with the distribution. ; ; * Neither the name of Fanning Software Consulting, Inc. nor the names of its ; ; contributors may be used to endorse or promote products derived from this ; ; software without specific prior written permission. ; ; ; ; THIS SOFTWARE IS PROVIDED BY FANNING SOFTWARE CONSULTING, INC. ''AS IS'' AND ANY ; ; EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES ; ; OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT ; ; SHALL FANNING SOFTWARE CONSULTING, INC. BE LIABLE FOR ANY DIRECT, INDIRECT, ; ; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED ; ; TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; ; ; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ; ; ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ; ; (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS ; ; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. ; ;******************************************************************************************; ; ;+ ; This funtion returns the number of meters per pixel for a particular zoom level ; in images returned using Google's Static Image API. ; ; :Categories: ; Utility ; ; :Params: ; zoomlevel: in, optional, type=integer, default=12 ; The Google zoom level used in retrieving Google Maps using the static image API. ; Documentation: https://developers.google.com/maps/documentation/staticmaps/. ; ; ; :Examples: ; For example, to find the meters per pixel for a zoom level of 12:: ; IDL> Print, cgGoogle_MetersPerPixel(12) ; 38.218514 ; ; :Author: ; FANNING SOFTWARE CONSULTING:: ; David W. Fanning ; 1645 Sheely Drive ; Fort Collins, CO 80526 USA ; Phone: 970-221-0438 ; E-mail: david@idlcoyote.com ; Coyote's Guide to IDL Programming: http://www.idlcoyote.com ; ; :History: ; Written, 20 June 2012. ; Updated the algorithm for determining meters per pixel to use WGS-84 equitorial radius ; based on suggestion by Alain LeCacheax. 11 Sept 2012. DWF. ; ; :Copyright: ; Copyright (c) 2012, Fanning Software Consulting, Inc. ;- Function cgGoogle_MetersPerPixel, zoomLevel Compile_Opt idl2 ; Return to the caller if there is an error. On_Error, 2 ; Need a zoom level? IF N_Elements(zoomLevel) EQ 0 THEN zoomLevel = 12 ; Number of pixels in an image with a zoom level of 0. pixels_in_image = 256 ; The equitorial radius of the Earth assuming WGS-84 ellipsoid. earth_radius = 6378137.0D ; The number of meters per pixel. metersPerPixel = (2*!DPI*earth_radius) / pixels_in_image / 2L^zoomLevel ; Return the value. RETURN, metersPerPixel END