Increase extent of vector layer with OGR or GDAL?
Question:
When using the OGR library or GDAL library with Python script, is it possible to increase the extent of a vector layer without actually adding new data points? In my specific case, I would like to increase the extent of vector layers associated with gpx files so that when I convert them to rasters they all have the same pixel matrix.
EDIT: An attempt of mine to use gdal.Rasterize
does not produce a “tiff” file, nor does it cause an error to be reported:
import os
import gdal
import ogr
import math
os.chdir(r'C:UserspipiDocumentsRogaineTarlogpx') #folder containing gpx files
vector_fn = '6_hour_Autumngaine_w_Tom_Elle.gpx' #filename of input gpxfile
pixel_size = 20 #units are in m if gpx file is left in wgs84
raster_fn = '0011a.tif' # Filename of the raster Tiff that will be created
driver = ogr.GetDriverByName('GPX')
source_ds = driver.Open(vector_fn, 0)
source_layer = source_ds.GetLayer('track_points') #returns the 'track points' layer of the data source
SR = source_layer.GetSpatialRef().ExportToWkt()
#_______USING VALUES FROM THE FILE___________
x_min1, x_max1, y_min1, y_max1 = source_layer.GetExtent()
pixel_sizey = pixel_size/(111.2*math.pow(10,3)) #determines an approximate x and y size because of geographic coordinates.
pixel_sizex = pixel_size/(math.cos(((y_max1 + y_min1)/2)*(math.pi/180))*111.2*math.pow(10,3))
print (pixel_sizey, pixel_sizex)
x_res = int((x_max1 - x_min1) / pixel_sizex)
y_res = int((y_max1 - y_min1) / pixel_sizey)
print (x_res, y_res)
layer_list = ['track_points']
gdal.Rasterize(raster_fn, vector_fn, format='GTiff', outputBounds=[x_min1, y_min1, x_max1, y_max1], outputSRS=SR, xRes=x_res, yRes=y_res, burnValues=[1], layers=layer_list)
target_ds = None
vector_fn = None
source_layer = None
source_ds = None
Answers:
I was unable to find a method to change the extent of the vector layer. However, I was able to write a python Function that uses gdal.RasterizeLayer() to produce a raster with an extent much larger than the original vector layer. The code for this function is:
import os
import gdal
import ogr
def RasterizeLarge(name, layer, extent, pixel_size):
"""Used to rasterize a layer where the raster extent is much larger than the layer extent
Arguments:
name -- (string) filename without extension of raster to be produced
layer -- (vector layer object) vector layer containing the data to be rasterized (tested with point data)
extent -- (list: x_min, x_max, y_min, y_max) extent of raster to be produced
pixel_size -- (list: x_pixel_size, y_pixel_size) 1 or 2 pixel different pixel sizes may be sent
"""
if isinstance(pixel_size, (list, tuple)):
x_pixel_size = pixel_size[0]
y_pixel_size = pixel_size[1]
else:
x_pixel_size = y_pixel_size = pixel_size
x_min, x_max, y_min, y_max = extent
# determines the x and y resolution of the file (lg = large)
x_res_lg = int((x_max - x_min) / x_pixel_size)+2
y_res_lg = int((y_max - y_min) / y_pixel_size)+2
if x_res_lg > 1 and y_res_lg > 1:
pass
else:
print ('Your pixel size is larger than the extent in one dimension or more')
return
x_min_sm, x_max_sm, y_min_sm, y_max_sm = layer.GetExtent()
if x_min_sm > x_min and x_max_sm < x_max and y_min_sm > y_min and y_max_sm < y_max:
pass
else:
print ('The extent of the layer is in one or more parts outside of the extent provided')
return
nx = int((x_min_sm - x_min)/x_pixel_size) #(number of pixels between main raster origin and minor raster)
ny = int((y_max - y_max_sm)/y_pixel_size)
x_res_sm = int((x_max_sm - x_min_sm) / x_pixel_size)+2
y_res_sm = int((y_max_sm - y_min_sm) / y_pixel_size)+2
#determines upper left corner of small layer raster
x_min_sm = x_min + nx * x_pixel_size
y_max_sm = y_max - ny * y_pixel_size
#______Creates a temporary raster file for the small raster__________
try:
# create the target raster file with 1 band
sm_ds = gdal.GetDriverByName('GTiff').Create('tempsmall.tif', x_res_sm, y_res_sm, 1, gdal.GDT_Byte)
sm_ds.SetGeoTransform((x_min_sm, x_pixel_size, 0, y_max_sm, 0, -y_pixel_size))
sm_ds.SetProjection(layer.GetSpatialRef().ExportToWkt())
gdal.RasterizeLayer(sm_ds, [1], layer, burn_values=[1])
sm_ds.FlushCache()
#______Gets data from the new raster in the form of an array________
in_band = sm_ds.GetRasterBand(1)
in_band.SetNoDataValue(0)
sm_data = in_band.ReadAsArray()
finally:
sm_ds = None #flushes data from memory. Without this you often get an empty raster.
#_____Creates an output file with the provided name and extent that contains the small raster.
name = name + '.tif'
try:
lg_ds = gdal.GetDriverByName('GTiff').Create(name, x_res_lg, y_res_lg, 1, gdal.GDT_Byte)
if lg_ds is None:
print 'Could not create tif'
return
else:
pass
lg_ds.SetProjection(layer.GetSpatialRef().ExportToWkt())
lg_ds.SetGeoTransform((x_min, x_pixel_size, 0.0, y_max, 0.0, -y_pixel_size))
lg_band = lg_ds.GetRasterBand(1)
lg_data = in_band.ReadAsArray()
lg_band.WriteArray(sm_data, xoff = nx, yoff = ny)
lg_band.SetNoDataValue(0)
lg_band.FlushCache()
lg_band.ComputeStatistics(False)
lg_band = None
finally:
del lg_ds, lg_band, in_band
os.remove('tempsmall.tif')
return
You need to pass options=gdal.RasterizeOptions(format='GTiff', outputBounds=[x_min1, y_min1, x_max1, y_max1], outputSRS=SR, xRes=x_res, yRes=y_res, burnValues=[1], layers=layer_list)
instead of passing the individual kwargs
directly. Otherwise, they will be ignored, and the command won’t do what you intend. See Link and Link for details and links to the source code (often useful given the terse documentation).
When using the OGR library or GDAL library with Python script, is it possible to increase the extent of a vector layer without actually adding new data points? In my specific case, I would like to increase the extent of vector layers associated with gpx files so that when I convert them to rasters they all have the same pixel matrix.
EDIT: An attempt of mine to use gdal.Rasterize
does not produce a “tiff” file, nor does it cause an error to be reported:
import os
import gdal
import ogr
import math
os.chdir(r'C:UserspipiDocumentsRogaineTarlogpx') #folder containing gpx files
vector_fn = '6_hour_Autumngaine_w_Tom_Elle.gpx' #filename of input gpxfile
pixel_size = 20 #units are in m if gpx file is left in wgs84
raster_fn = '0011a.tif' # Filename of the raster Tiff that will be created
driver = ogr.GetDriverByName('GPX')
source_ds = driver.Open(vector_fn, 0)
source_layer = source_ds.GetLayer('track_points') #returns the 'track points' layer of the data source
SR = source_layer.GetSpatialRef().ExportToWkt()
#_______USING VALUES FROM THE FILE___________
x_min1, x_max1, y_min1, y_max1 = source_layer.GetExtent()
pixel_sizey = pixel_size/(111.2*math.pow(10,3)) #determines an approximate x and y size because of geographic coordinates.
pixel_sizex = pixel_size/(math.cos(((y_max1 + y_min1)/2)*(math.pi/180))*111.2*math.pow(10,3))
print (pixel_sizey, pixel_sizex)
x_res = int((x_max1 - x_min1) / pixel_sizex)
y_res = int((y_max1 - y_min1) / pixel_sizey)
print (x_res, y_res)
layer_list = ['track_points']
gdal.Rasterize(raster_fn, vector_fn, format='GTiff', outputBounds=[x_min1, y_min1, x_max1, y_max1], outputSRS=SR, xRes=x_res, yRes=y_res, burnValues=[1], layers=layer_list)
target_ds = None
vector_fn = None
source_layer = None
source_ds = None
I was unable to find a method to change the extent of the vector layer. However, I was able to write a python Function that uses gdal.RasterizeLayer() to produce a raster with an extent much larger than the original vector layer. The code for this function is:
import os
import gdal
import ogr
def RasterizeLarge(name, layer, extent, pixel_size):
"""Used to rasterize a layer where the raster extent is much larger than the layer extent
Arguments:
name -- (string) filename without extension of raster to be produced
layer -- (vector layer object) vector layer containing the data to be rasterized (tested with point data)
extent -- (list: x_min, x_max, y_min, y_max) extent of raster to be produced
pixel_size -- (list: x_pixel_size, y_pixel_size) 1 or 2 pixel different pixel sizes may be sent
"""
if isinstance(pixel_size, (list, tuple)):
x_pixel_size = pixel_size[0]
y_pixel_size = pixel_size[1]
else:
x_pixel_size = y_pixel_size = pixel_size
x_min, x_max, y_min, y_max = extent
# determines the x and y resolution of the file (lg = large)
x_res_lg = int((x_max - x_min) / x_pixel_size)+2
y_res_lg = int((y_max - y_min) / y_pixel_size)+2
if x_res_lg > 1 and y_res_lg > 1:
pass
else:
print ('Your pixel size is larger than the extent in one dimension or more')
return
x_min_sm, x_max_sm, y_min_sm, y_max_sm = layer.GetExtent()
if x_min_sm > x_min and x_max_sm < x_max and y_min_sm > y_min and y_max_sm < y_max:
pass
else:
print ('The extent of the layer is in one or more parts outside of the extent provided')
return
nx = int((x_min_sm - x_min)/x_pixel_size) #(number of pixels between main raster origin and minor raster)
ny = int((y_max - y_max_sm)/y_pixel_size)
x_res_sm = int((x_max_sm - x_min_sm) / x_pixel_size)+2
y_res_sm = int((y_max_sm - y_min_sm) / y_pixel_size)+2
#determines upper left corner of small layer raster
x_min_sm = x_min + nx * x_pixel_size
y_max_sm = y_max - ny * y_pixel_size
#______Creates a temporary raster file for the small raster__________
try:
# create the target raster file with 1 band
sm_ds = gdal.GetDriverByName('GTiff').Create('tempsmall.tif', x_res_sm, y_res_sm, 1, gdal.GDT_Byte)
sm_ds.SetGeoTransform((x_min_sm, x_pixel_size, 0, y_max_sm, 0, -y_pixel_size))
sm_ds.SetProjection(layer.GetSpatialRef().ExportToWkt())
gdal.RasterizeLayer(sm_ds, [1], layer, burn_values=[1])
sm_ds.FlushCache()
#______Gets data from the new raster in the form of an array________
in_band = sm_ds.GetRasterBand(1)
in_band.SetNoDataValue(0)
sm_data = in_band.ReadAsArray()
finally:
sm_ds = None #flushes data from memory. Without this you often get an empty raster.
#_____Creates an output file with the provided name and extent that contains the small raster.
name = name + '.tif'
try:
lg_ds = gdal.GetDriverByName('GTiff').Create(name, x_res_lg, y_res_lg, 1, gdal.GDT_Byte)
if lg_ds is None:
print 'Could not create tif'
return
else:
pass
lg_ds.SetProjection(layer.GetSpatialRef().ExportToWkt())
lg_ds.SetGeoTransform((x_min, x_pixel_size, 0.0, y_max, 0.0, -y_pixel_size))
lg_band = lg_ds.GetRasterBand(1)
lg_data = in_band.ReadAsArray()
lg_band.WriteArray(sm_data, xoff = nx, yoff = ny)
lg_band.SetNoDataValue(0)
lg_band.FlushCache()
lg_band.ComputeStatistics(False)
lg_band = None
finally:
del lg_ds, lg_band, in_band
os.remove('tempsmall.tif')
return
You need to pass options=gdal.RasterizeOptions(format='GTiff', outputBounds=[x_min1, y_min1, x_max1, y_max1], outputSRS=SR, xRes=x_res, yRes=y_res, burnValues=[1], layers=layer_list)
instead of passing the individual kwargs
directly. Otherwise, they will be ignored, and the command won’t do what you intend. See Link and Link for details and links to the source code (often useful given the terse documentation).