[gdal-dev] gdalwarp help/bug

[savoie at nsidc.org]

Hi all,

I'm not sure if I'm doing something wrong or if I've found a bug in gdalwarp.  I thought I'd ask here before putting in a trac ticket. Please let me know if this is the wrong procedure.

In any event, I have posted steps and links on gis.stackexchange that shows horizontal artifacts in the middle of images created during simple calls to gdal warp.


Stack exchange link: http://gis.stackexchange.com/questions/116465/gdalwarp-leaves-horizontal-artifacts-regridding-from-ease-grid-laea-to-polarst

Text of link follows:


Hi there,

I'm trying to understand how to use gdalwarp to warp an image.  I believe I'm doing the basics correctly, but I might be missing some gdalwarp options?  Any help would be greatly appreciate.

The basic problem is that I see horizontal artifiacts in my output image.

Here's the steps to reproduce.

Start with a simple 722x722 image.  http://imgur.com/UiMBqSd  (you can save with http://imgur.com/UiMBqSd.png)

apply metadata to make this a geotiff (this is a EASE-grid Lambert Azimuthal Equal Area projection on a 1924 authallic sphere.)


gdal_translate -a_srs '+proj=laea +lat_0=90 +lon_0=0 +x_0=0 +y_0=0 +a=6371228 +b=6371228 +units=m +no_defs' \
    -a_ullr -4524688.262500000 4524688.262500000 4524688.262500000 -4524688.262500000  \
    -co COMPRESS=DEFLATE -co PREDICTOR=2 -co ZLEVEL=9 \
    -of GTiff ./UiMbqSd.png ./UiMbqSd.withmetadata.tif


This seems to have the expected geographic information (~12.5km grid) confirmed with gdalinfo


gdalinfo UiMBqSd.withmetadata.tif


Driver: GTiff/GeoTIFF
Files: UiMbqSd.withmetadata.tif
Size is 722, 722
Coordinate System is:
PROJCS["unnamed",
    GEOGCS["unnamed ellipse",
        DATUM["unknown",
            SPHEROID["unnamed",6371228,0]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433]],
    PROJECTION["Lambert_Azimuthal_Equal_Area"],
    PARAMETER["latitude_of_center",90],
    PARAMETER["longitude_of_center",0],
    PARAMETER["false_easting",0],
    PARAMETER["false_northing",0],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]]]
Origin = (-4524688.262500000186265,4524688.262500000186265)
Pixel Size = (12533.762500000000728,-12533.762500000000728)
Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  COMPRESSION=DEFLATE
  INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  (-4524688.263, 4524688.263) (135d 0' 0.00"W, 29d42'45.71"N)
Lower Left  (-4524688.263,-4524688.263) ( 45d 0' 0.00"W, 29d42'45.71"N)
Upper Right ( 4524688.263, 4524688.263) (135d 0' 0.00"E, 29d42'45.71"N)
Lower Right ( 4524688.263,-4524688.263) ( 45d 0' 0.00"E, 29d42'45.71"N)
Center      (   0.0000000,   0.0000000) (180d 0' 0.00"E, 90d 0' 0.00"N)
Band 1 Block=722x2 Type=Byte, ColorInterp=Red
  Mask Flags: PER_DATASET ALPHA
Band 2 Block=722x2 Type=Byte, ColorInterp=Green
  Mask Flags: PER_DATASET ALPHA
Band 3 Block=722x2 Type=Byte, ColorInterp=Blue
  Mask Flags: PER_DATASET ALPHA
Band 4 Block=722x2 Type=Byte, ColorInterp=Alpha


If I then try to regrid it.

gdalwarp -t_srs "+proj=stere +lat_0=90 +lon_0=-45 +lat_ts=70 +ellps=WGS84 +datum=WGS84 +units=m" ./UiMbqSd.withmetadata.tif ./regridded_lon0_-45.tif

The problem I'm seeing is horizontal artifacts that appear to protrude horizontally around the middle of the image.
You can see a png representation on imagur: http://imgur.com/Nrx4ZoS

This occurs even with different lat_0 values.
gdalwarp -t_srs "+proj=stere +lat_0=90 +lon_0=0 +lat_ts=70 +ellps=WGS84 +datum=WGS84 +units=m" ./UiMbqSd.withmetadata.tif ./regridded_lon0_0.tif

Another png representation on imagur:  http://imgur.com/uiiF9Ir


I'm currently running this on a mac:

> gdalwarp --version
GDAL 1.11.1, released 2014/09/24

But I've tested and seen the same behavior on ubuntu 12.04:
GDAL 1.10.1, released 2013/08/26

Any help solving this would be greatly appreciated.

Thanks
Matt





-- 
Matthew Savoie  -  Senior Software Developer
National Snow and Ice Data Center
(303) 735-0785   http://nsidc.org