Geographic Information Systems Asked by openwater on June 21, 2021
I would like to convert the individual records (polygons/features) of a shapefile to raster using GDAL/OGR. Here is the example shape and the mask raster. Rasterizing the full layer with all records (two, in this example) at once works:
from osgeo import gdal
from osgeo import ogr
from osgeo import gdalconst
raster_file = r"c:Tempmask.tif"
shape_file = r"c:Temptest2.shp"
# open raster and obtain extent and properties
data = gdal.Open(raster_file, gdalconst.GA_ReadOnly)
geo_transform = data.GetGeoTransform()
x_min = geo_transform[0]
y_max = geo_transform[3]
x_max = x_min + geo_transform[1] * data.RasterXSize
y_min = y_max + geo_transform[5] * data.RasterYSize
x_res = data.RasterXSize
y_res = data.RasterYSize
pixel_width = geo_transform[1]
# open shapefile and create layer
driver = ogr.GetDriverByName("ESRI Shapefile")
dataSource = driver.Open(shape_file, 0)
layer = dataSource.GetLayer()
# convert the layer with field 'presence' to raster
target_ds = gdal.GetDriverByName('GTiff').Create(r"C:Temptest2_rasterized.tif", x_res, y_res, 1, gdal.GDT_Byte)
target_ds.SetGeoTransform((x_min, pixel_width, 0, y_min, 0, pixel_width))
gdal.RasterizeLayer(target_ds, [1], layer, options=["ATTRIBUTE=presence"])
When I loop over the individual features, I can’t find a way to export the feature to raster:
from osgeo import gdal
from osgeo import ogr
from osgeo import gdalconst
import os
raster_file = r"c:Tempmask.tif"
shape_file = r"c:Temptest2.shp"
# open raster and obtain extent and properties
data = gdal.Open(raster_file, gdalconst.GA_ReadOnly)
geo_transform = data.GetGeoTransform()
x_min = geo_transform[0]
y_max = geo_transform[3]
x_max = x_min + geo_transform[1] * data.RasterXSize
y_min = y_max + geo_transform[5] * data.RasterYSize
x_res = data.RasterXSize
y_res = data.RasterYSize
pixel_width = geo_transform[1]
# open shapefile and create layer
driver = ogr.GetDriverByName("ESRI Shapefile")
dataSource = driver.Open(shape_file, 0)
layer = dataSource.GetLayer()
nr_features = layer.GetFeatureCount()
for feat_id in range(nr_features):
feature = layer.GetFeature(feat_id)
output = os.path.join(r"C:Temp", "rasterized"+str(feat_id)+".tif")
target_ds = gdal.GetDriverByName('GTiff').Create(output, x_res, y_res, 1, gdal.GDT_Byte)
target_ds.SetGeoTransform((x_min, pixel_width, 0, y_min, 0, pixel_width))
# this does not work since I do not pass a layer to the command
gdal.RasterizeLayer(target_ds, [1], feature, options=["ATTRIBUTE=presence"])
# e.g. is it possible to achieve it with Rasterize?
gdal.Rasterize(...)
Is what I am after at all possible using GDAL/OGR?
Or do I need a workaround like converting each feature to an individual layer and then rasterize each layer?
Complete workaround for converting each feature to an individual layer and then rasterize each one it can be observed in following code (where my own paths to layers were used):
from osgeo import gdal
from osgeo import ogr
from osgeo import gdalconst
import os
raster_file = "/home/zeito/pyqgis_data/mask.tif"
shape_file = "/home/zeito/pyqgis_data/test2.shp"
# open raster and obtain extent and properties
data = gdal.Open(raster_file, gdalconst.GA_ReadOnly)
geo_transform = data.GetGeoTransform()
x_min = geo_transform[0]
y_max = geo_transform[3]
x_max = x_min + geo_transform[1] * data.RasterXSize
y_min = y_max + geo_transform[5] * data.RasterYSize
x_res = data.RasterXSize
y_res = data.RasterYSize
pixel_width = geo_transform[1]
# open shapefile and create layer
driver = ogr.GetDriverByName("ESRI Shapefile")
dataSource = driver.Open(shape_file, 0)
layer = dataSource.GetLayer()
nr_features = layer.GetFeatureCount()
for feat_id in range(nr_features):
feature = layer.GetFeature(feat_id)
id_no = feature.GetField("id_no")
presence = feature.GetField("presence")
outShapefile = os.path.join("/home/zeito/pyqgis_data/", "feature" + str(feat_id)+".shp")
output = os.path.join("/home/zeito/pyqgis_data/", "rasterized" + str(feat_id)+".tif")
outDriver = ogr.GetDriverByName("ESRI Shapefile")
# Remove output shapefile if it already exists
if os.path.exists(outShapefile):
outDriver.DeleteDataSource(outShapefile)
# Create the output shapefile
outDataSource = outDriver.CreateDataSource(outShapefile)
outLayer = outDataSource.CreateLayer("feature" + str(feat_id), geom_type=ogr.wkbPolygon)
# Add an ID field
idField = ogr.FieldDefn("id_no", ogr.OFTInteger)
outLayer.CreateField(idField)
# Add a presence field
presField = ogr.FieldDefn("presence", ogr.OFTInteger)
outLayer.CreateField(presField)
# Create the feature and set values
featureDefn = outLayer.GetLayerDefn()
feat = ogr.Feature(featureDefn)
geom = feature.GetGeometryRef()
feat.SetGeometry(geom)
feat.SetField("id_no", id_no)
feat.SetField("presence", presence)
outLayer.CreateFeature(feat)
feat = None
# Save and close DataSource
outDataSource = None
target_ds = gdal.GetDriverByName('GTiff').Create(output, x_res, y_res, 1, gdal.GDT_Byte)
target_ds.SetGeoTransform((x_min, pixel_width, 0, y_min, 0, pixel_width))
new_dataSource = driver.Open(outShapefile, 0)
new_layer = new_dataSource.GetLayer()
# this works now
gdal.RasterizeLayer(target_ds, [1], new_layer, options=["ATTRIBUTE=presence"])
target_ds = None
new_dataSource = None
dataSource = None
After running above code at Python Console of QGIS 3.4, vector and raster layers were obtained as expected.
Initial situation:
Rasterized feature 0:
Rasterized feature 1:
Answered by xunilk on June 21, 2021
Not sure if anyone is struggling with this but I spent a day on this and the solution was simple. I was itereating through features in a shapefile to export images of a specific feature with an empty mask outside each features geometry. Easier than I thought but it took me a while.
feature = layer.GetFeature(i)
geom = feature.GetGeometryRef()
# gets extents to create image within
minX, maxX, minY, maxY = geom.GetEnvelope()
# convert geometry to json
json_coords = geom.ExportToJson() coordinate
# use the json coordinates as culineDSName
# and cropToCutline as True to create the mask with GdalWarp
output_options = gdal.WarpOptions(outputBounds=[minX, minY, maxX, maxY],
dstAlpha=True,
multithread=True,
cutlineDSName = json_coords,
cropToCutline=True)
gdal.Warp(output_file, Raster, options=output_options)
Answered by Mike Walters on June 21, 2021
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