Speed Up Polygon Grid Generation

There are many tools that generate regular uniform grids with geoprocessing, but I found a novel was of generating grids pretty quickly for large areas.  Rasters are fast and can be created on the fly easily using numpy.  To make the raster a feature class, ArcPy has a Raster to Polygon tool that should be available at all levels of desktop.

import arcpy
import numpy
import math
fc = r"c:\temp\somedata.shp" # assume projection is projected coordinate system not Lat/Long where measurements are in decimal degrees
width = 10000 # meters
height = 10000 # meters
#  Gets the feature classes' extent
#
desc = arcpy.Describe(fc)
extent = desc.extent
#   Set the Mask
#
arcpy.env.mask = fc
#   Calculate the number of columns
#

dist_x = math.sqrt(math.pow((extent.XMax - extent.XMin), 2))
dist_y = math.sqrt(math.pow((extent.YMax - extent.YMin),2))
col_x = int(dist_x / width)
col_y = int(dist_y / height)
if col_x % distanceMeters > 0:
   col_x += 1
if col_y % distanceMeters > 0:
  col_y += 1
#   Construct the structure numpy array with random values
#
numpyArray = (numpy.random.permutation(col_x * col_y) + 1).reshape(col_y, col_x)
#   Convert array to raster 
#
myData = arcpy.NumPyArrayToRaster(numpyArray,
                                  arcpy.Point(extent.XMin, extent.YMin),
                                  width, height)
#   Convert the raster to a polygon feature class
#
grid = r"%s\gridData" % arcpy.env.scratchGDB
grid = arcpy.RasterToPolygon_conversion(in_raster=myData,
                                            out_polygon_features=grid,
                                            simplify="NO_SIMPLIFY",
                                            raster_field="VALUE")[0]

The code takes the extent of the data and creates a grid. The mask environmental parameter essentially clips the raster to the shape of the feature class. This way you only gets cells within the given polygon area. If you wanted cells to fall outside the feature classes' shape, then just comment out that line.

So that is that.


If you haven't done so, check out ArcREST.
Also vote for my idea for a GUI builder for Python Add-Ins.

Playing with GeoPackages - Shrinking the Database

Awhile back Esri announced the support of the GeoPackage, which is just a sqlite database that holds vector data, and soon raster data too.

When you add and remove data to the sqlite database, it grows but never shrinks.  Think of it like a river that rises and falls, but the water line always remains.  This waterline is the space used on your hard drive.

To reduce the footprint of the database, you can run the VACUUM command to shrink the data base.

import sqlite3
import arcpy
SQLITE_FILE = r"c:\temp\example.gpkg"
conn = sqlite3.connect(SQLITE_FILE)
conn.execute("VACUUM")
conn.close()

Pretty simple to reduce the size of the database.  What VACUUM does is reconstruct the database from scratch. This will leave the database with an empty free-list and a file that is minimal in size. Note, however, that the VACUUM can take some time to run and it can use up to twice as much temporary disk space as the original file while it is running.

Enjoy