I think I have stumbled upon the solution for tiling the png image.
To re-project the PNG image, we can geo-reference the images with GDAL, then warp the geo-referenced image to the correct projection, also with GDAL.
The process is described here:
First, enter “gdalinfo Abies_fraseri.png” into terminal to get the bounds of the PNG image.
This yields the following output:
Upper Left ( 0.0, 0.0)
Lower Left ( 0.0, 1302.0)
Upper Right ( 2899.0, 0.0)
Lower Right ( 2899.0, 1302.0)
Center ( 1449.5, 651.0)
A template and implementation for our PNG files is demonstrated here:
gdal_translate -of VRT -a_srs EPSG:4326 -gcp 0 0 ULlong ULlat -gcp UPPERRIGHTPx 0 URlong URlat -gcp LOWERRIGHTPx LOWERRIGHTPy LRlong LRlat Abies_fraseri.png Abies_fraseri.vrt
gdal_translate -of VRT -a_srs EPSG:4326 -gcp 0 0 -84.000683874 35.7889383688 -gcp 2899.0 0 -83.0424855 35.7889383688 -gcp 2899.0 1302.0 -83.0424855 35.426963641 Abies_fraseri.png Abies_fraseri.vrt
For “ULlong” (Upper Left Long) and so forth I used a bounding box tool (http://boundingbox.klokantech.com
) to determine the following bounds of the PNG – however, if there is a more “official” known boundary, it would be wise to use that instead.
35.426963641,-84.000683874 – bottom left / lower left
35.426963641,-83.0424855 bottom right / lower right
35.7889383688,-83.0424855 – top right / upper right
35.7889383688,-84.000683874 – top left / upper left
Next, take the .vrt file and warp it:
gdalwarp -of VRT -t_srs EPSG:4326 Abies_fraseri.vrt Abies_fraseri_2.vrt
This creates a folder with tiles for a KML network link.
see “doc.kml” in the attached zip folder which you may open in Google Earth.
There is also an Open Map Layers HTML page in the attached zip folder.
To add trails in Google Earth
My opinion is it would be more interesting and informative to have the species occurrences added as a separate layer. Therefore, I would prefer to create placemarkers / waypoints for species locations rather than black squares on the images. Is it possible to generate PNG images with the likely distribution but not the black squares? If so, would that take a long time to re-do to make these tiled overlays?
Also, although I “hacked” the PNG bounds, I’m still worried it the overlay’s georeferencing be “off” a bit and would love to use a more trustworthy set of coordinates than those derived from my best judgement and http://boundingbox.klokantech.com.
From here, I think it would be smart to document a workflow for doing a lot of PNG to VRT to KML at a time. I haven’t tried processing a whole directory of images at once yet – just playing with the Abies_fraseri.png for now.