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On 23/06/2022 21:51, carlos h via
Qgis-user wrote:
Hello, I have an NDVI image that has a pixel of 4 centimeters,
that is, 16 square centimeters.
I have 2 doubts:
1. What method can I use to generalize the NDVI image to 1
square meter in pixel size?
One of the tools that you can use within QGIS to resample to a
coarser resolution is gdal_translate.
From the documentation you can set the target resolution:
- -tr <xres> <yres>
-
set target resolution. The values must
be expressed in georeferenced units.
Both must be positive values. This is mutually exclusive
with
-outsize and -a_ullr.
and then choose among these resampling methods:
-
-r {nearest (default),bilinear,cubic,cubicspline,lanczos,average,rms,mode}
-
Select a resampling algorithm.
nearest applies a nearest neighbour (simple
sampling) resampler
average computes the average of all non-NODATA
contributing pixels. Starting with GDAL 3.1, this is a
weighted average taking into account properly the weight of
source pixels not contributing fully to the target pixel.
rms computes the root mean squared / quadratic
mean of all non-NODATA contributing pixels (GDAL >= 3.3)
bilinear applies a bilinear convolution kernel.
cubic applies a cubic convolution kernel.
cubicspline applies a B-Spline convolution kernel.
lanczos applies a Lanczos windowed sinc
convolution kernel.
mode selects the value which appears most often
of all the sampled points.
See: https://gdal.org/programs/gdal_translate.html for the full
set of options.
2. When generalizing the NDVI image to 1 square
meter per pixel, what value does that new pixel take? the mean
value of all pixels in 1 square meter? the maximum value of the
pixels? etc, I ask this because if the original NDVI image has a
pixel of 4 centimeters (16 cm2), in 1 square meter there are
more or less 625 pixels, then what pixel value does it take if
it is generalized to 1 square meter? the average? the maximum
value?
Thank you very much
Carlos
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--
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918
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