[gdal-dev] Move pixel ULx ULy - what is dx_dy + dy_dx

[Clive Swan]

Greetings,

I want to shift the UL x, UL y of an image.

I am trying to find out what the *dx_dy + dy_dx* is.

The code is:

import gdal
### open dataset with update permission
ds = gdal.Open('/data/coastal-2020.tif', gdal.GA_Update)
### get the geotransform as a tuple of 6
gt = ds.GetGeoTransform()
### unpack geotransform into variables
x_tl = (-180.0000000)
x_res = 0.000800000000000
*dx_dy* =
y_tl =  (90.0000000)
*dy_dx* =
y_res = -0.000800000000000

x_tl, x_res, *dx_dy*, y_tl, *dy_dx*, y_res = gt

# compute shift of 1 pixel RIGHT in X direction
shift_x = 1 * x_res
# compute shift of 2 pixels UP in Y direction
# y_res likely negative, because Y decreases with increasing Y index
shift_y = -2 * y_res

# make new geotransform
gt_update = (x_tl + shift_x, x_res, dx_dy, y_tl + shift_y, dy_dx, y_res)


>From gdalinfo:
Size is 450000, 225000
Coordinate System is:
GEOGCRS["WGS 84",
    DATUM["World Geodetic System 1984",
        ELLIPSOID["WGS 84",6378137,298.257223563,
            LENGTHUNIT["metre",1]]],
    PRIMEM["Greenwich",0,
        ANGLEUNIT["degree",0.0174532925199433]],
    CS[ellipsoidal,2],
        AXIS["geodetic latitude (Lat)",north,
            ORDER[1],
            ANGLEUNIT["degree",0.0174532925199433]],
        AXIS["geodetic longitude (Lon)",east,
            ORDER[2],
            ANGLEUNIT["degree",0.0174532925199433]],
    ID["EPSG",4326]]
Data axis to CRS axis mapping: 2,1
Origin = (-180.000000000000000,90.000000000000000)
Pixel Size = (0.000800000000000,-0.000800000000000)

Image Structure Metadata:
  COMPRESSION=LZW
  INTERLEAVE=BAND
  PREDICTOR=3
Corner Coordinates:
Upper Left  (-180.0000000,  90.0000000) (180d 0' 0.00"W, 90d 0' 0.00"N)
Lower Left  (-180.0000000, -90.0000000) (180d 0' 0.00"W, 90d 0' 0.00"S)
Upper Right ( 180.0000000,  90.0000000) (180d 0' 0.00"E, 90d 0' 0.00"N)
Lower Right ( 180.0000000, -90.0000000) (180d 0' 0.00"E, 90d 0' 0.00"S)
Center      (   0.0000000,   0.0000000) (  0d 0' 0.01"E,  0d 0' 0.01"N)



-- 

 Regards,


Clive Swan

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