How can I get product pixel size (resolution) from snappy (Python)?

development python
#1

It is quite easy to get raster width and height using snappy:

firstBand=prod.getBands()[0]
width = firstBand.getRasterWidth()
height = firstBand.getRasterHeight()

but I can’t http://step.esa.int/docs/v5.0/apidoc/engine/org/esa/snap/core/datamodel/AbstractBand.html a method to get a particular pixel size, so that I will know the spatial resolution of my raster file.

#2

I’ve tried to implement this as follows:

https://github.com/kedziorm/mySNAPscripts/commit/df300bf702980e15ef0327594a1c67eb14332bdc

but it seems that my function returns different resolution/pixel size than that which can see gdalinfo (file which I used in testing is contained within the repository):

myResolutionFunctionReturnsSomethingWrong.png1612×817 242 KB

Since gdalinfo do not handle all ESA SNAP formats, I can’t just call gdalinfo in my script.
I thought about converting each product to GeoTIFF firstly and then call gdalinfo, but it will be very time consuming.

#3

In most cases it is sufficient to compute the resolution just at the centre pixel.

#4

As far as I understand your calculations correctly, at least part of the problems lies in the way your trying to extract the corners coodinates. By taking the min/max lat/lon values and calculating the difference to get the extent, you obtain the extent along a particular longitude or latitude without considering the fact of the rotation of the scene relative to the lat/lon grid - i.e. two corner points have no lat or lon value in common.

Maybe try the following and see if this works out:

import numpy as np
import snappy
from geographiclib.geodesic import Geodesic

def calc_pixel_size(prod):
    corner_top_left = prod.getSceneGeoCoding().getGeoPos(snappy.PixelPos(0,0), None)
    corner_bottom_left = prod.getSceneGeoCoding().getGeoPos(snappy.PixelPos(0, prod.getSceneRasterHeight()), None)
    corner_top_right = prod.getSceneGeoCoding().getGeoPos(snappy.PixelPos(prod.getSceneRasterWidth(), 0), None)
    height_range_m = Geodesic.WGS84.Inverse(corner_top_left.getLat(), corner_top_left.getLon(), corner_bottom_left.getLat(), corner_bottom_left.getLon())["s12"]
    width_range_m = Geodesic.WGS84.Inverse(corner_top_left.getLat(), corner_top_left.getLon(), corner_top_right.getLat(), corner_top_right.getLon())["s12"]
    height_n_pixels = prod.getSceneRasterHeight()
    width_n_pixels = prod.getSceneRasterWidth()
    mean_pixel_size = (round(height_range_m/height_n_pixels,2), round(width_range_m/width_n_pixels,2))
    mean_pixel_size
    return mean_pixel_size