Map Projections, Utilities
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.
An image warped into the output map projection is returned.
- 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 (
- 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.
- 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
MapInmap 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
XYRangeof 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.
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)
FANNING SOFTWARE CONSULTING:
David W. Fanning 1645 Sheely Drive Fort Collins, CO 80526 USA Phone: 970-221-0438 E-mail: firstname.lastname@example.org Coyote's Guide to IDL Programming: http://www.idlcoyote.com
Copyright (c) 2012, Fanning Software Consulting, Inc.
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.
|Modification date:||Wed Feb 20 13:51:26 2013|