[gdal-dev] gdalwarp on a .vrt: Using internal nodata values (eg 0) for image (?)

[Ari Simmons]

One notably huge difference is that there is a huge jump in pixel size
(from 0.000833333333323 to 205.686440189378940)...

ah, duh. Unit change.

On Thu, Jun 11, 2015 at 2:26 PM, Ari Simmons <ari.ucb.fire at gmail.com> wrote:

> I am experimenting with using 'gdalwarp' on a .vrt (first time), but I'm
> not sure what I'm doing wrong. I've been running this:
>
> >> gdalwarp -s_srs EPSG:4326 -t_srs EPSG:3857 -r bilinear -of VRT
> merged.vrt srtm_merged_3857.vrt
>
> and it processes fast (far far *too fast* for this global file) and returns
>
> >> Creating output file that is 194835P X 479814L.
> >> Processing input file merged.vrt
> >> Using internal nodata values (eg. 0) for image merged.vrt
>
> The return .vrt file definitely doesn't appear right...a quick look at the
> returned file:
>
> input:
>
> Size is 432000, 208800
> 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 = (-180.000416666666670,84.000416666666666)
> Pixel Size = (0.000833333333323,-0.000833333333323)
> Corner Coordinates:
> Upper Left  (-180.0004167,  84.0004167) (180d 0' 1.50"W, 84d 0' 1.50"N)
> Lower Left  (-180.0004167, -89.9995833) (180d 0' 1.50"W, 89d59'58.50"S)
> Upper Right ( 179.9995833,  84.0004167) (179d59'58.50"E, 84d 0' 1.50"N)
> Lower Right ( 179.9995833, -89.9995833) (179d59'58.50"E, 89d59'58.50"S)
> Center      (  -0.0004167,  -2.9995833) (  0d 0' 1.50"W,  2d59'58.50"S)
> Band 1 Block=128x128 Type=Int16, ColorInterp=Gray
>   NoData Value=0
>   Overviews: 216000x104400, 108000x52200, 54000x26100, 27000x13050,
> 13500x6525,
> 6750x3263, 3375x1632, 1688x816, 844x408, 422x204
>
> and output file:
>
>  Size is 193861,
> 479814                                                          Coordinate
> System is:
> PROJCS["WGS 84 /
> Pseudo-Mercator",
> GEOGCS["WGS
> 84",
> DATUM["WGS_1984",
> SPHEROID["WGS
> 84",6378137,298.257223563,
> AUTHORITY["EPSG","7030"]],
> AUTHORITY["EPSG","6326"]],
> PRIMEM["Greenwich",0,
> AUTHORITY["EPSG","8901"]],
> UNIT["degree",0.0174532925199433,
> AUTHORITY["EPSG","9122"]],
> AUTHORITY["EPSG","4326"]],
> PROJECTION["Mercator_1SP"],
> PARAMETER["central_meridian",0],
> PARAMETER["scale_factor",1],
> PARAMETER["false_easting",0],
> PARAMETER["false_northing",0],
> UNIT["metre",1,
> AUTHORITY["EPSG","9001"]],
> AXIS["X",EAST],
> AXIS["Y",NORTH],
> EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0
> +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext
> +no_defs"],
> AUTHORITY["EPSG","3857"]]
> Origin =
> (-19837179.642485119000000,18807657.848855246000000)
> Pixel Size =
> (205.686440189378940,-205.686440189378940)                         Corner
> Coordinates:
> Upper Left  (-19837179.642,18807657.849) (178d12' 1.50"W, 84d 0'
> 1.50"N)        Lower Left  (-19837179.642,-79883575.764) (178d12' 1.50"W,
> 89d59'58.50"S)       Upper Right (20037399.339,18807657.849)
> (179d59'56.47"E, 84d 0' 1.50"N)         Lower Right
> (20037399.339,-79883575.764) (179d59'56.47"E, 89d59'58.50"S)
> Center      (  100109.848,-30537958.958) (  0d53'57.49"E, 89d
> 2'43.78"S)        Band 1 Block=512x128 Type=Int16,
> ColorInterp=Gray                                 Overviews: 96931x239907,
> 48466x119954, 24233x59977, 12117x29989, 6059x14995, 3030x7498, 1515x3749,
> 758x1875, 379x938, 191x471
>
> One notably huge difference is that there is a huge jump in pixel size
> (from 0.000833333333323 to 205.686440189378940)...
>
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