Hi,
I think I've come up with an acceptable workflow for creating a geotiff of a non-map based image - specifically for use within Neatline.
1. Original Image Size (w/h)
3813 x 2304
2. Determine the desired scale.
I found using EPSG:3857 easier to work with while attempting to plot this globally, we'll later covert to EPSG:4326.
Using EPSG:3857, I then found that w/h x 1500 produced an image about the size of the US.
3. generate new w/h based on scale
5719500 x 3456000
4. Position the image so it's center point resides at 0,0 on the map (off the western coast of Africa).
This will ensure the least amount of distortion. Simply divide each dimension by 2. Depending on the height of your image, you may need to modify this and scale your w/h differently.
5. Convert image to GeoTiff
gdal_translate -of GTiff -a_srs EPSG:3857 -a_ullr -2859750 1728000 2859750 -1728000 in.tif out_3857.tif
6. Convert from 3857 to 4326
gdalwarp -s_srs EPSG:3857 -t_srs EPSG:4326 out_3857.tif out_4326.tif
7. Check your resulting file.
Its center should be at 0,0 and its coords should be in degrees. You'll notice that the newly computed w/h are different from the original. I am OK with this amount of distortion, but if anyone knows of a more precise way to accomplish this, please float it my way.
8. gdalinfo out_4326.tif
Driver: GTiff/GeoTIFF
Files: out_4326.tif
Size is 3825, 2284
Coordinate System is:
GEOGCS["WGS 84",
DATUM["WGS_1984",
SPHEROID["WGS 84",6378137,298.257223563,
AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433],
AUTHORITY["EPSG","4326"]]
Origin = (-25.689571337608008,15.336401859896865)
Pixel Size = (0.013431623571063,-0.013431623571063)
Metadata:
AREA_OR_POINT=Area
Image Structure Metadata:
INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left ( -25.6895713, 15.3364019) ( 25d41'22.46"W, 15d20'11.05"N)
Lower Left ( -25.6895713, -15.3414264) ( 25d41'22.46"W, 15d20'29.13"S)
Upper Right ( 25.6863888, 15.3364019) ( 25d41'11.00"E, 15d20'11.05"N)
Lower Right ( 25.6863888, -15.3414264) ( 25d41'11.00"E, 15d20'29.13"S)
Center ( -0.0015913, -0.0025123) ( 0d 0' 5.73"W, 0d 0' 9.04"S)
Band 1 Block=3825x1 Type=Byte, ColorInterp=Red
Band 2 Block=3825x1 Type=Byte, ColorInterp=Green
Band 3 Block=3825x1 Type=Byte, ColorInterp=Blue