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

[Andrew Simpson]

Thanks for the reply.  I've included the input file information below.

I understand that I should see skewing.  What's the best method for
correction of the skew?

I misspoke a bit about the tiles.  I had a few sets of 100 tiles each.  on
each 100 tile set, the output size was 30gb.  The total size of the input
files were only about 7.5GB.  I think what actually is happening is that
when I received the tiles from my source, i did not get the entire set.
Instead I got an "L" shape of actual data.  When I go to build the
vrt/single .tif file, I'm getting a black layer added to the missing
tiles.  In essence, gdal is filling in the missing data with black tiles,
thus increasing the size.  I was also adding pyramids, which is adding some
to the size.  For my application, I do not need the pyramids, so I will
just not at them going forward.

Here is the input info:
PROJCS["NAD_1983_UTM_Zone_12N",
    GEOGCS["NAD83",
        DATUM["North_American_Datum_1983",
            SPHEROID["GRS 1980",6378137,298.2572221010002,
                AUTHORITY["EPSG","7019"]],
            AUTHORITY["EPSG","6269"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4269"]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",-111],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",500000],
    PARAMETER["false_northing",0],
    UNIT["meters",1],
    AUTHORITY["EPSG","26912"]]
Origin = (300000.000000000000000,3537000.000000000000000)
Pixel Size = (0.300000000000000,-0.300000000000000)
Metadata:
  AREA_OR_POINT=Area
  TIFFTAG_RESOLUTIONUNIT=1 (unitless)
  TIFFTAG_SOFTWARE=Inpho GmbH
  TIFFTAG_XRESOLUTION=1
  TIFFTAG_YRESOLUTION=1
Image Structure Metadata:
  INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  (  300000.000, 3537000.000) (113d 6'57.86"W, 31d57' 4.92"N)
Lower Left  (  300000.000, 3535500.000) (113d 6'56.75"W, 31d56'16.23"N)
Upper Right (  301500.000, 3537000.000) (113d 6' 0.76"W, 31d57' 5.87"N)
Lower Right (  301500.000, 3535500.000) (113d 5'59.65"W, 31d56'17.18"N)
Center      (  300750.000, 3536250.000) (113d 6'28.76"W, 31d56'41.05"N)
Band 1 Block=128x128 Type=Byte, ColorInterp=Red
Band 2 Block=128x128 Type=Byte, ColorInterp=Green
Band 3 Block=128x128 Type=Byte, ColorInterp=Blue
PROJ.4 string is:
'+proj=utm +zone=12 +datum=NAD83 +units=m +no_defs '



Andrew Simpson

On Thu, Feb 12, 2015 at 4:20 PM, David Strip <gdal at stripfamily.net> wrote:

>  While you've shown us your output is in unprojected (lon/lat) WGS84
> coordinates, you haven't told us about your input - only that it's datum is
> NAD83. If the inputs are projected, you should expect to see skewing, since
> a rectangular area in projected coordinates in general does not map to a
> rectangle in lon/lat.
>
> As to size - you took 300 tiles each about 50-75M and made a single file.
> Your input is in the 20GB range, so 30 GB is not out of hand. Are your
> input tiles compressed? Your output is NOT compressed, so that would go a
> long way towards explaining things.
>
>
> On 2/12/2015 5:58 AM, Andrew Simpson wrote:
>
> 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
>
>
> _______________________________________________
> gdal-dev mailing listgdal-dev at lists.osgeo.orghttp://lists.osgeo.org/mailman/listinfo/gdal-dev
>
>
>
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