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For example, on the gdalinfo documentation, we have

gdalinfo ~/openev/utm.tif
Driver: GTiff/GeoTIFF
Size is 512, 512
Coordinate System is:
PROJCS["NAD27 / UTM zone 11N",
    GEOGCS["NAD27",
        DATUM["North_American_Datum_1927",
            SPHEROID["Clarke 1866",6378206.4,294.978698213901]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",-117],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",500000],
    PARAMETER["false_northing",0],
    UNIT["metre",1]]
Origin = (440720.000000,3751320.000000)
Pixel Size = (60.000000,-60.000000)
Corner Coordinates:
Upper Left  (  440720.000, 3751320.000) (117d38'28.21"W, 33d54'8.47"N)
Lower Left  (  440720.000, 3720600.000) (117d38'20.79"W, 33d37'31.04"N)
Upper Right (  471440.000, 3751320.000) (117d18'32.07"W, 33d54'13.08"N)
Lower Right (  471440.000, 3720600.000) (117d18'28.50"W, 33d37'35.61"N)
Center      (  456080.000, 3735960.000) (117d28'27.39"W, 33d45'52.46"N)
Band 1 Block=512x16 Type=Byte, ColorInterp=Gray

What does a size of 512, 512 represent?

What is the origin, and what is pixel size?

I'm new to GIS, and so I don't really understand what they represent, and can't find anything online to explain this.

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5
  • Hi - 512,512 is pixel size. Hopefully, this might help you! gdal.org/programs/gdalinfo.html#
    – Chris Jenner
    Commented Jul 18, 2019 at 17:40
  • I've just realised the above is a copy from the link I sent over sorry! It does say in there though 'Raster size (in pixels and lines)'
    – Chris Jenner
    Commented Jul 18, 2019 at 17:41
  • 1
    @ChrisJenner thank you! Don't know how I missed that. What about other stuff like the origin and pixel size though?
    – Madan
    Commented Jul 18, 2019 at 17:46
  • 1
    This is all explained in any introduction to GIS. Searching finds me this: youtube.com/watch?v=ptAtnc-U20A
    – Spacedman
    Commented Jul 18, 2019 at 17:47
  • @madan at a quick look to me it looks like its the top left x & y coordinates of your GeoTiff. I'm not too sure on the 'Pixel Size' part though sorry!
    – Chris Jenner
    Commented Jul 18, 2019 at 17:47

1 Answer 1

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3

The coordinate reference system helps to georeference the raster to the earth. At the end of the PROJCS description is the linear unit of measure: "Metre". That also sets the unit for the pixel size of 60.0 (metres).

Size is the number of pixels in the easting (left-right) and northing (up-down) directions. The northing value is negative because the start point (0,0 in pixel coordinates) is at the upper left corner--so it's counting down.

Origin is the same as the upper left corner of the image.

The corner coordinates are listed in the projected coordinate reference system of UTM 11 North. The values in parentheses are in degrees-minutes-seconds.

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2
  • "That also sets the unit for the pixel size of 60.0 (metres)." As in a single pixel is 60 metres? Isn't this the same as spatial resolution?
    – Madan
    Commented Jul 18, 2019 at 18:37
  • Yes, that's correct.
    – mkennedy
    Commented Jul 18, 2019 at 18:42

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