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A Python library that allows for the creation and population of OGC GeoPackage databases with write access

Project description

pygeopkg

pygeopkg is a Python compatible library that allows for the creation and population of (write-to) an OGC GeoPackage database, including creating features within this resource. GeoPackages can be opened and viewed software solutions built for viewing and analyzing spatial data, including ArcGIS and QGIS.

For more details on OGC GeoPackages, please see the OGC web page.

Installation

pygeopkg was created to work as a packaged sub-respository in a larger Python library. As such, users should simply add this repository as a sub-repository via git to their main repository or download the files and add them to their projects as they see fit.

Python Compatibility

The pygeopkg library is compatible with Python 2+ and Python 3+.

Usage

pygeopkg can be used to:

  • Create a new empty GeoPackage from scratch.
  • Create new Feature Classes within a GeoPackage.
  • Populate Feature Classes with geometry and attributes. (see Steps 3 & 4)

Step 1 - Create An Empty GeoPackage

from pygeopkg.core.geopkg import GeoPackage

# Creates an empty geopackage
gpkg = GeoPackage.create(r'c:\temp\test.gpkg')

Geopackages are created with three default Spatial References defined automatically, a pair of Spatial References to handle undefined cases, and a WGS 84 entry.

The definition of the WGS84 entry is flexible - meaning that the WKT for WGS84 can be setup per the users liking. As an example, use with Esri's ArcGIS means either using the EPSG WKT or the ESRI WKT. By default the ESRI WKT is used - However, if EPSG WKT is desired, you may provide a flavor parameter to the create method specifying EPSG.

# Creates an empty geopackage
gpkg = GeoPackage.create(r'c:\temp\test.gpkg', flavor='EPSG')

Step 2 - Create A New Feature Class

To create a new Feature Class in the empty GeoPackage, you will need to tell the GeoPackage the Spatial Reference of the Feature Class and the schema (e.g., fields) to be available in the Feature Class.

A Feature Class can be created with Z or M (or both) enabled. If either of these options are enabled, the geometry inserted into the Feature Class must include a value for the option specified.

from pygeopkg.core.geopkg import GeoPackage
from pygeopkg.core.srs import SRS
from pygeopkg.core.field import Field
from pygeopkg.shared.enumeration import GeometryType, SQLFieldTypes

gpkg = GeoPackage.create(r'c:\temp\test.gpkg')

srs_wkt = (
    'PROJCS["WGS_1984_UTM_Zone_23N",'
    'GEOGCS["GCS_WGS_1984",'
    'DATUM["D_WGS_1984",'
    'SPHEROID["WGS_1984",6378137.0,298.257223563]],'
    'PRIMEM["Greenwich",0.0],'
    'UNIT["Degree",0.0174532925199433]],'
    'PROJECTION["Transverse_Mercator"],'
    'PARAMETER["False_Easting",500000.0],'
    'PARAMETER["False_Northing",0.0],'
    'PARAMETER["Central_Meridian",-45.0],'
    'PARAMETER["Scale_Factor",0.9996],'
    'PARAMETER["Latitude_Of_Origin",0.0],'
    'UNIT["Meter",1.0]]')

srs = SRS('WGS_1984_UTM_Zone_23N', 'EPSG', 32623, srs_wkt)
fields = (
    Field('int_fld', SQLFieldTypes.integer),
    Field('text_fld', SQLFieldTypes.text),
    Field('test_fld_size', SQLFieldTypes.text, 100),
    Field('test_bool', SQLFieldTypes.boolean))

fc = gpkg.create_feature_class(
    'test', srs, fields=fields, shape_type=GeometryType.point)

About Spatial References For GeoPackages

Spatial References in GeoPackages are somewhat loosely defined. You may provide a Spatial Reference of any definition and from any authority - be that EPSG, ESRI, or another source. This library follows this lead and has no restriction on the definitions provided. However, it should be noted that if you would like Feature Classes to be readable by major software packages, you should provide a definition which the software can read appropriately. For example, our testing has found that ArcMap prefers definitions corresponding to its own WKT format.

A very simple Spatial Reference object is provided with this package for convenience. It requires the name, authority, Spatial Reference ID, and Spatial Reference well known text. This object should be used when creating a Feature Class.

Step 3 - Insert Records Into A Feature Class

Records can be inserted into a Feature Class using the insert_rows method. This method inserts all the rows with a single sql call to get the best performance.

Geometry fields on gpkg Feature Classes created by this code base will always be named SHAPE. Geometry inserted into this field must always be WKB. To create WKB, use the utility functions from the conversion subpackage. Currently utility functions exists to handle points, lines and polygons (including Z and M varieties).

This example shows the creation of a random point Feature Class and builds upon the code from previous examples. Note that the create Feature Class portion of the code is omitted...

from random import choice, randint
from string import ascii_uppercase, digits
from pygeopkg.conversion.to_geopkg_geom import (
    point_to_gpkg_point, make_gpkg_geom_header)
from pygeopkg.shared.constants import SHAPE
from pygeopkg.core.geopkg import GeoPackage

# NOTE: Builds from previous examples 
# and assumes existing GeoPackage and feature class!

gpkg = GeoPackage(r'c:\temp\test.gpkg')
fc = gpkg.get_feature_class('test')

# Field objects can also be used
field_names = [SHAPE, 'int_fld', 'text_fld']

# Generate the geometry header once because it is always the same
point_geom_hdr = make_gpkg_geom_header(fc.srs.srs_id)

# Generate some random points and attributes
rows = []
for i in range(10000):
    rand_str = ''.join(choice(ascii_uppercase + digits) for _ in range(10))
    rand_int = randint(0, 1000)
    rand_x = randint(300000, 600000)
    rand_y = randint(1, 100000)
    wkb = point_to_gpkg_point(point_geom_hdr, rand_x, rand_y)
    rows.append((wkb, rand_int, rand_str))

fc.insert_rows(field_names, rows)

Step 4 - Creating OGC Geometry Well Known Binaries

As mentioned, this library supports the creation of point, line, and polygon well known binaries. Functions supporting these capabilities can be found in pygeopkg.conversion.to_geopkg_geom.

Examples are provided below and further examples can be found in the tests. See code documentation for more details as warranted.

It is important to note that Z and M capabilities are defined at the time a Feature Class is created. If a Feature Class is Z or M enabled, then a value must be provided for that value. Be sure to pick the correct conversion function depending on the Z and M combination desired.

Point Example

A binary header with srs details is always needed but (in pygeopkg) is the same for all features in a Feature Class. For best performance, create this once.

# Point in WGS 84
x, y = -119, 34
hdr = make_gpkg_geom_header(4326)
gpkg_wkb = point_to_gpkg_point(hdr, x, y)

Line Example

The utility function for creating lines expects a list of points representing its vertices.

# Line with ZM Values for use with UTM Zone 23N (WGS 84)
line = [(300000, 1, 10, 0), (300000, 4000000, 20, 1000),
        (700000, 4000000, 30, 2000), (700000, 1, 40, 3000)]
hdr = make_gpkg_geom_header(32623)
gpkg_wkb = points_zm_to_gpkg_line_string_zm(hdr, line)

Polygon Example

The utility function for creating regular polygons expects a list of rings where a ring is simply the list of points it contains.

rings = [[(300000, 1), (300000, 4000000), (700000, 4000000),
          (700000, 1), (300000, 1)]]
hdr = make_gpkg_geom_header(32623)
gpkg_wkb = point_lists_to_gpkg_polygon(hdr, rings)

Roadmap

  • Write unpackers so that this package can be used to extract data from GeoPackages. Focus is currently on writing. Unpackers specific to this package exist for testing only.
  • Write a more thorough implementation of the individual geometry headers.

License

MIT

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