CGCHANGEMAPPROJECTION

CGCHANGEMAPPROJECTION
This function warps a map projected image from one map projection to another, using
Map_Proj_Image to do the warping. Useful in general, it is used specifically to
warp map projected images into the Equirectangular map projection with a WGS 84 ellipsoid
that is used by Google Earth. See the program `cgImage2KML` to see how it is used.

Returns

An image warped into the output map projection is returned.

Params

image: in, required
Any 2D or true-color image with or without an alpha channel. This image will
be warped to the output map projection (`mapOut`).
mapin: in, required, type=object
A map coordinate object (cgMap) describing the map projection and coordinates of the
input image that is to be warped.

Keywords

boundary: in, optional, type=dblarr
A four-element array specifying the Cartesian (XY) coordinates of the input
image range, in the form [xmin, ymin, xmax, ymax]. If this parameter is not
present, the boundary will be obtained from the `MapIn` map coordinate object.
On output, this variable will contain the Cartesian boundary of the warped image.
bilinear: in, optional, type=boolean, default=0
Set this keyword to warp the image with bilinear interpolation. The default is
to do nearest neighbor interpolation.
latlonbox: out, optional, type=fltarr
A four-element float array containing the boundaries of the warped image in
the [north, south, east, west] form preferred by Google Earth. Listed as degrees.
mapout: in, optional, type=object
A map coordinate object (cgMap) describing the map projection and coordinates of the
warped image. This image will be warped into this map projection. The [XY]Range of
this object will be set to the `XYRange` of the output image.
mask: out, optional
Set this keyword equal to a named variable that will contain a byte array of the same
dimensions as the output image, containing a mask of the “good” values. Values in the output
image that were set to `Missing` (that is, the values were off the map) will have a mask value
of 0, while all other mask values will be 1.
missing: in, optional, type=integer, default=0
Set this keyword equal to an integer value to be used for pixels that fall outside of
the valid map coordinates. The default value is 0.
xyrange: out, optional, type=dblarr
The Cartesian (XY) coordinates associated with the output image. These are the map image
boundaries of the output image.

Examples

To prepare a GeoTiff file for creating a KML overlay on Google Earth::
netObject = Obj_New('IDLnetURL')
url = 'http://www.idlcoyote.com/data/AF03sep15b.n16-VIg.tif'
returnName = netObject -> Get(URL=url, FILENAME=AF03sep15b.n16-VIg.tif')
Obj_Destroy, netObject
map = cgGeoMap('AF03sep15b.n16-VIg.tif')
googleMap = Obj_New('cgMap', 'Equirectangular', Ellipsoid='WGS 84')
warpedImage = cgChangeMapProjection(image, map, MAPOUT=googleMap)

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

Change History::
Written, 30 October 2012 by David W. Fanning.
Fixed a problem with a TRANSPOSE command for true-color images. Bad logic. 4 Jan 2012. DWF.
Fixed a problem in which Map_Proj_Image was not handling true-color image warping correctly
and also a problem with handling missing values passed from cgImage2KML correctly. 20 Feb 2013. DWF.
Forgot to specify the default value for MISSING. 25 Feb 2014. DWF.

Library	Coyote

Version	July-2015