From a199b0a2ef37a3b46ee8ef9032e7979473ec40df Mon Sep 17 00:00:00 2001
From: "Daniel.Frisinghelli" <daniel.frisinghelli@eurac.edu>
Date: Tue, 12 Jan 2021 14:09:18 +0100
Subject: [PATCH] Added a function to calculate the extent of a low-resolution
pixel in a high resolution image.
---
pysegcnn/core/utils.py | 65 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 65 insertions(+)
diff --git a/pysegcnn/core/utils.py b/pysegcnn/core/utils.py
index 79ba0e6..6260ed4 100644
--- a/pysegcnn/core/utils.py
+++ b/pysegcnn/core/utils.py
@@ -2271,3 +2271,68 @@ def extract_by_mask(src_ds, mask_ds, trg_ds, overwrite=False):
# clear source and mask dataset
del src_ds, mask_ds
+
+
+def pixels_within_lowres(top_left, res_prop):
+ """Calculate the position of high-res pixels within a low-res pixel.
+
+ .. important:
+
+ This function assumes that the low-resolution and high-resolution image
+ have the same georeferenced origin, i.e. the same top left corner in
+ physical coordinates.
+
+ Parameters
+ ----------
+ top_left : `tuple`
+ The top left corner indices of the low-resolution pixel in the
+ low-resolution image.
+ res_prop : `int` or `float`
+ The proportion of the low-resolution to the high-resolution.
+
+ Returns
+ -------
+ indices : `tuple` [:py:class:`numpy.ndarray`]
+ The indices of the high-resolution pixels within the high-resolution
+ image, which are fully-covered by the extent of the low-resolution
+ pixel ``top_left``.
+
+ Example
+ -------
+
+ The resolution of the low-resolution image is 250m, the one of the
+ high-resolution image is 30m, thus ``res_prop=250/30``. Assume that the
+ top left corner of the pixel of interest in the low-resolution image is
+ given by the position ``top_left=(0, 1)``. In the high-resolution
+ image, the top left corner of the pixel of interest is hence located
+ at ``top_left * res_prop``. This function returns the indices of all
+ the pixels in the high-resolution image, which are fully-covered by
+ the low-resolution pixel with position ``top-left``.
+
+ """
+ # the top left corner of a pixel in the low resolution image
+ xtl_lres, ytl_lres = top_left
+
+ # Note: only high-resolution pixel which are fully-covered by the
+ # low-resolution pixel are considered.
+
+ # the top left corner of the first pixel in the high resolution image,
+ # which lies within the extent of the low-resolution pixel
+ xtl_hres, ytl_hres = (np.ceil(xtl_lres * res_prop).astype(np.int),
+ np.ceil(ytl_lres * res_prop).astype(np.int))
+
+ # the bottom right corner of last pixel in the high resolution image,
+ # which lies within the extent of the low-resolution pixel
+ xbl_hres, ybl_hres = (np.floor((xtl_lres + 1) * res_prop).astype(np.int),
+ np.floor((ytl_lres + 1) * res_prop).astype(np.int))
+
+ # the range of the indices in the high-resolution image
+ xhres = np.arange(xtl_hres, xbl_hres, 1)
+ yhres = np.arange(ytl_hres, ybl_hres, 1)
+
+ # the indices of all the high-resolution pixels, which fully lie within
+ # the extent of the low-resolution pixel
+ indices = (np.repeat(xhres, repeats=len(yhres)),
+ np.tile(yhres, reps=len(xhres)))
+
+ return indices
--
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