[gdal-dev] new to gdal, converting projection, need some help

[Andrew Simpson]

I'm new to learning GDAL (mapping in general).  I have a bunch of tif files
(300+) that are in NAD83, but my mapping application only uses WGS84.  The
tiles are all around 50-75Mb each

I'm able to use gdal warp to convert the projection properly to WGS84, but
the images (tiles) come out skewed.

I tried using bdalbuildvrt first to create the vrt, then gdalwarp with the
following options:  -co TILED=YES -co BIGTIFF=YES -of GTIFF -t_srs
"+proj=longlat +datum=WGS84 + no_defs" input.vrt output.vrt

Ok, so this mostly works, but I have 2 questions/issues:
1.  what is the best way to convert the projection and eliminate the
skewing?
2.  The single .tif produced is now >30GB!  significantly larger.  why does
this occur and how can I keep this file size down?


Thanks for any info!
Andrew Simpson
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