# Source code for rios.pixelgrid

```
#!/usr/bin/env python
"""
Utility class PixelGridDefn, which defines a pixel grid,
plus useful operations on it.
Utility function findCommonRegion() to find the union
or intersection region of a list GDAL datasets, in a
reference grid.
"""
# This file is part of RIOS - Raster I/O Simplification
# Copyright (C) 2012 Sam Gillingham, Neil Flood
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
from . import imageio
from . import rioserrors
from . import fileinfo
from osgeo import osr
from osgeo import gdal
[docs]class PixelGridDefn(object):
"""
Definition of a pixel grid, including
the size and extent, and by implication the
resolution and alignment.
Methods are defined for relationships with
other instances, including:
* intersection()
* union()
* reproject()
* alignedWith()
* isComparable()
Attributes defined on the object:
* xMin
* xMax
* yMin
* yMax
* xRes
* yRes
* projection
The bounds define the external corners of the image, i.e. the
top-left corner of the top-left pixel, through to the bottom-right
corner of the bottom-right pixel. This is consistent with GDAL
conventions.
The projection is given as a WKT string.
The constructor takes the projection, the number of rows and columns,
and EITHER a complete GDAL geotransform tuple, OR a grid specified
with all the extent limits and the pixel resolutions (xRes and yRes).
If the geotransform is given, then the xMin, xMax, xRes and so on
are calculated from it.
"""
def __init__(self, geotransform=None, nrows=None, ncols=None, projection=None,
xMin=None, xMax=None, yMin=None, yMax=None, xRes=None, yRes=None):
"""
Can define in terms of a GDAL geotransform plus
the number of rows and columns.
Can also be defined by giving xMin, xMax, yMin, yMax,
and xRes, yRes directly.
Projection is given as a WKT string.
"""
self.projection = projection
self.xMin = xMin
self.xMax = xMax
self.yMin = yMin
self.yMax = yMax
self.xRes = xRes
self.yRes = yRes
if geotransform is not None and nrows is not None and ncols is not None:
self.xRes = geotransform[1]
self.yRes = abs(geotransform[5])
self.xMin = geotransform[0]
self.yMax = geotransform[3]
self.xMax = self.xMin + ncols * self.xRes
self.yMin = self.yMax - nrows * self.yRes
def __str__(self):
s = "xMin:%s,xMax:%s,yMin:%s,yMax:%s,xRes:%s,yRes:%s" % (self.xMin, self.xMax,
self.yMin, self.yMax, self.xRes, self.yRes)
return s
[docs] def alignedWith(self, other):
"""
Returns True if self is aligned with other. This means that
they represent the same grid, with different extents.
Alignment is checked within a small tolerance, so that exact
floating point matches are not required. However, notionally it
is possible to get a match which shouldn't be. The tolerance is
calculated as::
tolerance = 0.01 * pixsize / npix
and if a mis-alignment is <= tolerance, it is assumed to be zero.
For further details, read the source code.
"""
aligned = True
if not self.isComparable(other):
aligned = False
# Calculate a tolerance, based on the pixel size and the number of pixels,
# so that when the tolerance is accumulated across the whole grid, the
# total still comes out to be well under a pixel.
# First get the largest dimension of either grid
npix = self.getNumPix(self.xMax, self.xMin, self.xRes)
npix = max(npix, self.getNumPix(other.xMax, other.xMin, other.xRes))
npix = max(npix, self.getNumPix(self.yMax, self.yMin, self.yRes))
npix = max(npix, self.getNumPix(other.yMax, other.yMin, other.yRes))
res = min(self.xRes, self.yRes)
tolerance = 0.001 * res / npix
xMinSnapped = self.snapToGrid(self.xMin, other.xMin, self.xRes)
if abs(xMinSnapped - self.xMin) > tolerance:
aligned = False
yMaxSnapped = self.snapToGrid(self.yMax, other.yMax, self.yRes)
if abs(yMaxSnapped - self.yMax) > tolerance:
aligned = False
return aligned
[docs] def intersection(self, other):
"""
Returns a new instance which is the intersection
of self and other.
"""
if not self.isComparable(other):
return None
xMin = max(self.xMin, other.xMin)
xMax = min(self.xMax, other.xMax)
yMin = max(self.yMin, other.yMin)
yMax = min(self.yMax, other.yMax)
if xMin >= xMax or yMin >= yMax:
msg = "Images don't intersect"
raise rioserrors.IntersectionError(msg)
newPixelGrid = PixelGridDefn(xMin=xMin, xMax=xMax, yMin=yMin, yMax=yMax,
xRes=self.xRes, yRes=self.yRes, projection=self.projection)
return newPixelGrid
[docs] def union(self, other):
"""
Returns a new instance which is the union of self
with other.
"""
if not self.isComparable(other):
return None
xMin = min(self.xMin, other.xMin)
xMax = max(self.xMax, other.xMax)
yMin = min(self.yMin, other.yMin)
yMax = max(self.yMax, other.yMax)
newPixelGrid = PixelGridDefn(xMin=xMin, xMax=xMax, yMin=yMin, yMax=yMax,
xRes=self.xRes, yRes=self.yRes, projection=self.projection)
return newPixelGrid
[docs] def isComparable(self, other):
"""
Checks whether self is comparable with other. Returns
True or False. Grids are comparable if they have equal pixel
size, and the same projection.
"""
comparable = True
# Check resolution
if not self.equalPixSize(other):
comparable = False
# Check projection
if not self.equalProjection(other):
comparable = False
return comparable
[docs] def equalPixSize(self, other):
"""
Returns True if pixel size of self is equal to that of other.
Currently only checks absolute equality, probably should
work out a tolerance.
"""
return (self.xRes == other.xRes and self.yRes == other.yRes)
[docs] def equalProjection(self, other):
"""
Returns True if the projection of self is the same as the
projection of other
"""
selfProj = str(self.projection) if self.projection is not None else ''
otherProj = str(other.projection) if other.projection is not None else ''
srSelf = osr.SpatialReference(wkt=selfProj)
srOther = osr.SpatialReference(wkt=otherProj)
return bool(srSelf.IsSame(srOther))
[docs] def equivalentProjection(self, otherspatialref, pixtolerance):
"""
Similar to equalProjection but does a less accurate test
by checking converting coordinates from projection of self
to otherspatialref and checking they are within pixtolerance
pixels of each other.
The coordinates used for this are the four corners and centre
of image.
"""
srSelf = osr.SpatialReference(str(self.projection))
fileinfo.preventGdal3axisSwap(srSelf)
# Make a private copy of the other SR, to avoid damaging what they gave us.
otherspatialrefCopy = osr.SpatialReference(wkt=otherspatialref.ExportToWkt())
fileinfo.preventGdal3axisSwap(otherspatialrefCopy)
transform = osr.CoordinateTransformation(srSelf, otherspatialrefCopy)
xtol = pixtolerance * self.xRes
ytol = pixtolerance * self.yRes
points = []
points.append((self.xMin, self.yMax)) # upper left
points.append((self.xMax, self.yMax)) # upper right
points.append((self.xMax, self.yMin)) # bottom right
points.append((self.xMin, self.yMin)) # bottom left
points.append((self.xMin + ((self.xMax - self.xMin) / 2),
self.yMin + ((self.yMax - self.yMin) / 2))) # middle
equal = True
for (x, y) in points:
(otherx, othery, z) = transform.TransformPoint(x, y)
if abs(x - otherx) > xtol or abs(y - othery) > ytol:
equal = False
break
return equal
[docs] def makeGeoTransform(self):
"""
Returns a GDAL geotransform tuple from bounds and resolution
"""
geotransform = (self.xMin, self.xRes, 0.0, self.yMax, 0.0, -self.yRes)
return geotransform
[docs] def reproject(self, targetGrid):
"""
Returns a new instance which is the reprojection
of self to be in the same projection and pixel size
as targetGrid
"""
srSelf = osr.SpatialReference(str(self.projection))
fileinfo.preventGdal3axisSwap(srSelf)
srTarget = osr.SpatialReference(str(targetGrid.projection))
fileinfo.preventGdal3axisSwap(srTarget)
t = osr.CoordinateTransformation(srSelf, srTarget)
(tl_x, tl_y, z) = t.TransformPoint(self.xMin, self.yMax)
(bl_x, bl_y, z) = t.TransformPoint(self.xMin, self.yMin)
(tr_x, tr_y, z) = t.TransformPoint(self.xMax, self.yMax)
(br_x, br_y, z) = t.TransformPoint(self.xMax, self.yMin)
xMin = min(tl_x, bl_x)
xMax = max(tr_x, br_x)
yMin = min(bl_y, br_y)
yMax = max(tl_y, tr_y)
# Snap bounds to align with those in target grid
xMin = self.snapToGrid(xMin, targetGrid.xMin, targetGrid.xRes)
xMax = self.snapToGrid(xMax, targetGrid.xMin, targetGrid.xRes)
yMin = self.snapToGrid(yMin, targetGrid.yMin, targetGrid.yRes)
yMax = self.snapToGrid(yMax, targetGrid.yMin, targetGrid.yRes)
# Construct a new pixel grid object
newPixelGrid = PixelGridDefn(xMin=xMin, xMax=xMax, yMin=yMin, yMax=yMax,
xRes=targetGrid.xRes, yRes=targetGrid.yRes, projection=targetGrid.projection)
return newPixelGrid
[docs] def getDimensions(self):
"""
Utility method which returns the number of rows and columns
in the grid. Returns a tuple::
(nrows, ncols)
calculated from the min/max/res values.
"""
nrows = self.getNumPix(self.yMax, self.yMin, self.yRes)
ncols = self.getNumPix(self.xMax, self.xMin, self.xRes)
return (nrows, ncols)
[docs] @staticmethod
def roundAway(x):
"""
Simulates Python 2 round behavour
This is what we want as it rounds away from 0.
The decimal module seems to be the only way to do this properly
"""
import decimal
dec = decimal.Decimal(x).quantize(decimal.Decimal('1'),
rounding=decimal.ROUND_HALF_UP)
return float(dec.to_integral_value())
[docs] @staticmethod
def getNumPix(gridMax, gridMin, gridRes):
"""
Works out how many pixels lie between the given min and max,
at the given resolution. This is for internal use only.
"""
npix = int(PixelGridDefn.roundAway((gridMax - gridMin) / gridRes))
return npix
[docs] @staticmethod
def snapToGrid(val, valOnGrid, res):
"""
Returns the nearest value to val which is a whole multiple of
res away from valOnGrid, so that val is effectively on the same
grid as valOnGrid. This is for internal use only.
"""
diff = val - valOnGrid
numPix = diff / res
numWholePix = PixelGridDefn.roundAway(numPix)
snappedVal = valOnGrid + numWholePix * res
return snappedVal
[docs]def findCommonRegion(gridList, refGrid, combine=imageio.INTERSECTION):
"""
Returns a PixelGridDefn for the combination of all the grids
in the given gridList. The output grid is in the same coordinate
system as the reference grid.
The combine parameter controls whether UNION, INTERSECTION
or BOUNDS_FROM_REFERENCE is performed.
"""
newGrid = refGrid
if combine != imageio.BOUNDS_FROM_REFERENCE:
for grid in gridList:
if not newGrid.alignedWith(grid):
grid = grid.reproject(refGrid)
if combine == imageio.INTERSECTION:
newGrid = newGrid.intersection(grid)
elif combine == imageio.UNION:
newGrid = newGrid.union(grid)
return newGrid
[docs]def pixelGridFromFile(filename):
"""
Create a PixelGridDefn object for the given image file
"""
ds = gdal.Open(filename)
geotransform = ds.GetGeoTransform()
nrows = ds.RasterYSize
ncols = ds.RasterXSize
projection = ds.GetProjection()
pixgrid = PixelGridDefn(geotransform=geotransform, nrows=nrows, ncols=ncols,
projection=projection)
return pixgrid
```