cggoogle_metersperpixel.pro
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; 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