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 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 NOTE: The bounds defined 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 in accordance with GDAL conventions. """ 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)) transform = osr.CoordinateTransformation(srSelf, otherspatialref) 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)) srTarget = osr.SpatialReference(str(targetGrid.projection)) 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