Hobu in ArcUser
The April-June 2005 issue of ArcUser contains an article by Hobu on pages 34-36. It's an introduction to Python and GIS, and vector, grid, and raster processing with ogr.py and gdal.py for users of ArcGIS 9 -- which includes Python and makes a small subset of its functionality scriptable. Good writing, too bad he seems to have retired from blogging ;)
I ventured further into the magaine and found myself comparing the agility of ArcGIS and the GDAL/OGR Python modules while reading the tutorial on pages 46-49 ("Creating Accurate Footprints of Registered Aerial Images"). It's a rather involved and round-about manual process requiring an expensive ArcGIS add-on (Spatial Analyst). I'm sure that one could also manage to open a beer bottle using dentistry tools, but not as readily as with a bottle opener. Consider the following Python script:
# Create footprint shapefile import ogr driver = ogr.GetDriverByName('ESRI Shapefile') footprints_shp = driver.CreateDataSource('footprints.shp') footprints = footprints_shp.CreateLayer('footprints', geom_type=ogr.wkbPolygon) fd = ogr.FieldDefn('FILENAME', ogr.OFTString) fd.SetWidth(30) footprints.CreateField(fd) # Loop over a number of georeferenced images import glob import gdal files = glob.glob('*.jpg') for file in files: # Get georeferencing and size of imagery dataset = gdal.Open(file) g = dataset.GetGeoTransform() pixels = dataset.RasterXSize lines = dataset.RasterYSize minx = g maxx = minx + pixels * g maxy = g miny = maxy + lines * g # append to the 'footprints' layer wkt = 'POLYGON ((%f %f, %f %f, %f %f, %f %f, %f %f))' \ % (minx, miny, minx, maxy, maxx, maxy, maxx, miny, minx, miny) g = ogr.CreateGeometryFromWkt(wkt) f = ogr.Feature(feature_def=footprints.GetLayerDefn()) f.SetField(0, file) f.SetGeometryDirectly(g) footprints.CreateFeature(f) f.Destroy() # destroy footprints_shp to flush and close footprints_shp.Destroy()
No fooling about -- directly to the imagery bounds and write a polygon. Simple and straight-forward, the right tool for the job.