Is it okay that reprojection from UTM (EPSG:32612) to Web Mercator (EPSG:3857) with gdalwarp changes pixel size? Why does this happen? Does that mean that unit is not meters? If so, than how to convert pixel size from UTM units to Web Mercator units?
Command:
gdalwarp -t_srs "+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" LC08_L1TP_047011_20170518_20170519_01_RT_B4.TIF output.tif
Input image is Landsat 8 from AWS: http://landsat-pds.s3.amazonaws.com/c1/L8/047/011/LC08_L1TP_047011_20170518_20170519_01_RT/LC08_L1TP_047011_20170518_20170519_01_RT_B4.TIF
Original image info:
$ gdalinfo LC08_L1TP_047011_20170518_20170519_01_RT_B4.TIF
Driver: GTiff/GeoTIFF
Files: /home/user/Desktop/Landsat_sample/LC08_L1TP_047011_20170518_20170519_01_RT_B4.TIF
Size is 8451, 8491
Coordinate System is:
PROJCS["WGS 84 / UTM zone 12N",
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["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["metre",1,
AUTHORITY["EPSG","9001"]],
AXIS["Easting",EAST],
AXIS["Northing",NORTH],
AUTHORITY["EPSG","32612"]]
Origin = (488985.000000000000000,7851615.000000000000000)
Pixel Size = (30.000000000000000,-30.000000000000000)
Metadata:
AREA_OR_POINT=Point
Image Structure Metadata:
COMPRESSION=DEFLATE
INTERLEAVE=BAND
Corner Coordinates:
Upper Left ( 488985.000, 7851615.000) (111d17'58.67"W, 70d46' 6.92"N)
Lower Left ( 488985.000, 7596885.000) (111d16' 8.84"W, 68d29' 3.48"N)
Upper Right ( 742515.000, 7851615.000) (104d25'49.46"W, 70d39' 3.78"N)
Lower Right ( 742515.000, 7596885.000) (105d 5'39.63"W, 68d22'48.67"N)
Center ( 615750.000, 7724250.000) (108d 1'24.05"W, 69d36' 5.29"N)
Band 1 Block=512x512 Type=UInt16, ColorInterp=Gray
Reprojected image info:
$ gdalinfo output.tif
Driver: GTiff/GeoTIFF
Files: out.tif
out.tif.aux.xml
Size is 8902, 8880
Coordinate System is:
PROJCS["unnamed",
GEOGCS["unnamed ellipse",
DATUM["unknown",
SPHEROID["unnamed",6378137,0]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433]],
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"]]]
Origin = (-12389818.176861140877008,11323689.164804801344872)
Pixel Size = (85.895238477817642,-85.895238477817642)
Metadata:
AREA_OR_POINT=Point
Image Structure Metadata:
INTERLEAVE=BAND
Corner Coordinates:
Upper Left (-12389818.177,11323689.165) (111d17'58.67"W, 70d46' 7.79"N)
Lower Left (-12389818.177,10560939.447) (111d17'58.67"W, 68d22'48.98"N)
Upper Right (-11625178.764,11323689.165) (104d25'50.73"W, 70d46' 7.79"N)
Lower Right (-11625178.764,10560939.447) (104d25'50.73"W, 68d22'48.98"N)
Center (-12007498.470,10942314.306) (107d51'54.70"W, 69d36'28.82"N)
Band 1 Block=8902x1 Type=UInt16, ColorInterp=Gray
Min=0.000 Max=52607.000
Minimum=0.000, Maximum=52607.000, Mean=17537.063, StdDev=16780.853
Metadata:
STATISTICS_MAXIMUM=52607
STATISTICS_MEAN=17537.062597405
STATISTICS_MINIMUM=0
STATISTICS_STDDEV=16780.852772678
-t_srs EPSG:3857. What is the output of gdalinfo if you do that?$ gdalwarp -t_srs EPSG:3857 LC08_L1TP_047011_20170518_20170519_01_RT_B4.TIF out3857.tifCreating output file that is 8902P x 8880L. Processing input file LC08_L1TP_047011_20170518_20170519_01_RT_B4.TIF. 0...10...20...30...40...50...60...70...80...90...100 - done.gdalwarpis doing the right thing: keeping the total resolution. Forcing pixelsize with-tris the wrong way to go for most use-cases.