1

this is a rather simple and trivial question, but before I contact my supervisor I want to get sure. I have a .tif image that says the resolution is 4.5 x 4.5 mm. The output of gdalinfo is: Pixel Size = (0.004545650000000,-0.004545649999975). When I look at the image it looks very pixelated.

In my view a 4.5 mm resolution means that one pixel displays 4.5 mm x4.5 mm of the real view?

EDIT

Size is 53243, 11916
    PROJCS["WGS 84 / UTM zone 32N",
        GEOGCS["WGS 84",
            DATUM["WGS_1984",
                SPHEROID["WGS 84",6378137,298.257223563,
                    AUTHORITY["EPSG","7030"]],
                TOWGS84[0,0,0,0,0,0,0],
                AUTHORITY["EPSG","6326"]],
            PRIMEM["Greenwich",0],
            UNIT["degree",0.0174532925199433],
            AUTHORITY["EPSG","4326"]],
        PROJECTION["Transverse_Mercator"],
        PARAMETER["latitude_of_origin",0],
        PARAMETER["central_meridian",9],
        PARAMETER["scale_factor",0.9996],
        PARAMETER["false_easting",500000],
        PARAMETER["false_northing",0],
        UNIT["metre",1,
            AUTHORITY["EPSG","9001"]],
        AUTHORITY["EPSG","32632"]]
    Origin = (357377.652999999991152,5610076.298999999649823)
    Pixel Size = (0.004545650000000,-0.004545649999975)
    Metadata:
      AREA_OR_POINT=Area
    Image Structure Metadata:
      INTERLEAVE=PIXEL
    Band 1 Block=256x256 Type=Byte, ColorInterp=Red
      Unit Type: metre
    Band 2 Block=256x256 Type=Byte, ColorInterp=Green
      Unit Type: metre
    Band 3 Block=256x256 Type=Byte, ColorInterp=Blue
      Unit Type: metre

    Corner Coordinates:
    Upper Left  (  357377.653, 5610076.299) (  6d59' 0.91"E, 50d37'30.36"N)
    Lower Left  (  357377.653, 5610022.133) (  6d59' 0.99"E, 50d37'28.61"N)
    Upper Right (  357619.677, 5610076.299) (  6d59'13.22"E, 50d37'30.57"N)
    Lower Right (  357619.677, 5610022.133) (  6d59'13.30"E, 50d37'28.82"N)
    Center      (  357498.665, 5610049.216) (  6d59' 7.11"E, 50d37'29.59"N

)
  • What are the CRS and extent of the image? – Mazu_R Jul 22 '18 at 8:30
  • Or do you need the corner coordinates? – Lau Jul 22 '18 at 8:54
  • In a photo of a flat surface most pixels will not equal 4.5mm of the real object due to angles and optical effects - so 4.5 could be a mean, or it could be a theoretical value for an object at given distance in the center. The values you got with gdalinfo are for all intents and purposes the same, so i guess it's a theoretical value, or one for a raster image of a map) - gdalinfo will output Pixel Size in Degrees, btw. explaining the negative value. - At least for the E-W direction in the image this would translate to about 500 meters per pixel (north-west depending on position on globe) – bukwyrm Jul 22 '18 at 9:24
  • @ bukwyrm @Jae I added now almost the complete gdalinfo and it says that the unit is meter. Or does the meter unit only apply on some properties? – Lau Jul 22 '18 at 10:05
  • Add some other information from gdalinfo as well, the size or image in pixels and/or the corner coordinates. Do you know that the image is for sure of such high resolution? 10000x10000 pixels would then cover an area of 45 by 45 meters which is of course possible if it is acquired with a drone. – user30184 Jul 22 '18 at 10:30
5

PROJCS details the coordinate system, the first line is:

PROJCS["WGS 84 / UTM zone 32N",

and then it says:

    UNIT["metre",1,

which means that these numbers:

Origin = (357377.652999999991152,5610076.298999999649823)
Pixel Size = (0.004545650000000,-0.004545649999975)

are in metres. So that's a 4.5mm x 4.5mm pixel size, which is what we would call the resolution.

I notice that the band data says:

Band 1 Block=256x256 Type=Byte, ColorInterp=Red
  Unit Type: metre

but that's the unit of measurement of the data in each band rather than the location - for example if this is height data in each pixel. That measurement may also have a "resolution" depending on how it was measured, that would be the smallest difference in height that the instrument can detect.

3

Based on your added information of the CRS I would say yes (Pixel size = 4.5 x 4.5 mm), even if the resolution is extremely high. The unit of measurement is metre.

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