H2GIS Python

This is a python package that allows to manipulate H2GIS spatial database using a GraalVM-compiled native library and a C interface.

Main points

• Installation: Installation and setup instructions.
• H2GIS class: Detailed documentation for the H2GIS class.
• Example: Example usage of the library.

If you want information about h2gis you can go to the h2gis website.

Installation

Requirements

• Python 3.7+
• Native H2GIS shared library compiled with GraalVM
• Supported platforms: Linux, Windows, macOS

Install the Python Package

pip install .

Ensure the native library file is present in the following structure:

h2gis/
├── lib/
│   ├── h2gis.so      # Linux
│   ├── h2gis.dylib   # macOS
│   └── h2gis.dll     # Windows

Custom Library Path

You can specify a custom path to the native library:

from h2gis import H2GIS

db = H2GIS(lib_path="/custom/path/to/h2gis.so")


# H2GIS Class

## Overview

`H2GIS` is a Python class that wraps a native shared library compiled with GraalVM. It provides access to an embedded H2GIS database using GraalVM isolate and thread objects.

## Constructor

```python
H2GIS(lib_path=None)

• lib_path: Optional path to the .so, .dll, or .dylib file. If not provided, a default path is used based on the current OS.

Methods

connect(db_file: str, username="sa", password="")

Connect to a local H2GIS database file.

execute(sql: str) -> int

Execute an INSERT, UPDATE, or DELETE SQL statement.

fetch(sql: str) -> list[str]

Execute a SELECT SQL query and return results as a list of strings (one per row).

close()

Close the active database connection.

__del__()

Destructor that automatically tears down the GraalVM isolate and closes any connection.

H2GIS Class

Overview

H2GIS is a Python class that wraps a native shared library compiled with GraalVM. It provides access to an embedded H2GIS database using GraalVM isolate and thread objects.

Constructor

H2GIS(lib_path=None)

• lib_path: Optional path to the .so, .dll, or .dylib file. If not provided, a default path is used based on the current OS.

Methods

connect(db_file: str, username="sa", password="")

Connect to a local H2GIS database file.

execute(sql: str) -> int

Execute an INSERT, UPDATE, or DELETE SQL statement.

commit() -> int

Commit the current transaction by executing COMMIT;.

rollback() -> int

Rollback the current transaction by executing ROLLBACK;.

fetch(query: str, row_index: int = 1, stringformat="utf-8") -> dict[str, list]

Execute a SELECT SQL query and return all result rows as a typed dictionary. Each key is a column name, and each value is a list of column values.

parse_string_buffer(buf: bytes, num_rows: int) -> list[str | None]

Parse a buffer of length-prefixed UTF-8 strings or null entries.

parse_geometry_buffer(buf: bytes, num_rows: int) -> List[Optional[BaseGeometry]]

Parse a buffer of WKB geometry entries and return a list of Shapely geometry objects or None.

deserialize_resultset_buffer(buf: bytes) -> dict[str, list]

Deserialize the binary buffer returned by the native fetch_all function into a dictionary of columns with typed values.

isConnected() -> bool

Return True if a database connection is currently active and responsive.

ping() -> bool

Check if the database connection is alive by executing a test query.

close()

Close the current database connection but leave the isolate active.

deleteAndClose()

Delete the database file (if applicable) and close the connection.

Usage Examples

Basic Example

from h2gis import H2GIS
import geopandas as gpd
import pandas as pd
from shapely.wkt import loads as wkt_loads
import json
import matplotlib.pyplot as plt  # Import matplotlib
import ast

# Connexion and data import
h2gis = H2GIS("/mydb/path/dbName")
h2gis.execute("""
        DROP TABLE IF EXISTS LIEUX;
        CREATE TABLE LIEUX (
            ID INT PRIMARY KEY AUTO_INCREMENT,
            NOM VARCHAR(255),
            DESCRIPTION VARCHAR(255),
            THE_GEOM GEOMETRY(GEOMETRY)
        );
        INSERT INTO LIEUX (NOM, DESCRIPTION, THE_GEOM) VALUES ('Paris', 'Capitale de la France', ST_GeomFromText('POINT(2.3522 48.8566)', 4326));
        INSERT INTO LIEUX (NOM, DESCRIPTION, THE_GEOM) VALUES ('Lyon', 'Ville gastronomique', ST_GeomFromText('POINT(4.8357 45.7640)', 4326));
        INSERT INTO LIEUX (NOM, DESCRIPTION, THE_GEOM) VALUES ('Marseille', 'Port méditerranéen', ST_GeomFromText('POINT(5.3698 43.2965)', 4326));
        INSERT INTO LIEUX (NOM, DESCRIPTION, THE_GEOM) VALUES ('Englobant', 'Géométrie englobante', ST_GeomFromText('POLYGON((
        -4.72 48.42,
        -1.35 47.23,
        0.88 47.90,
        2.35 48.86,
        4.08 49.33,
        5.70 49.00,
        6.65 48.16,
        7.75 48.58,
        7.27 47.50,
        6.75 46.15,
        6.00 45.45,
        4.90 44.50,
        4.20 43.80,
        5.3698 43.2965,
        3.50 43.00,
        2.50 42.50,
        0.50 42.80,
        -1.00 43.40,
        -1.80 44.50,
        -2.50 45.80,
        -2.90 46.80,
        -3.50 47.80,
        -4.72 48.42
    ))', 4326)
);
""")

# Fetch the select query
fetch = h2gis.fetch("SELECT NOM, DESCRIPTION, THE_GEOM as geometry FROM LIEUX;")
print(fetch)

# Convert as dataframe
gdf = gpd.GeoDataFrame(fetch, geometry="GEOMETRY", crs="EPSG:4326")
print(gdf)

# Gest distance between first two points
if len(gdf) >= 2:
    paris_geom = gdf[gdf['NOM'] == 'Paris'].geometry.iloc[0]
    lyon_geom = gdf[gdf['NOM'] == 'Lyon'].geometry.iloc[0]
    dist_paris_lyon = paris_geom.distance(lyon_geom) * 111319.9

    print(f"Distance in meters between poit 1 and 2: {dist_paris_lyon:.2f} m")
else:
    print("2 geometries needed to calculate a distance")

print("connected : ", h2gis.isConnected())
h2gis.close()

# Display data
gdf.plot(edgecolor='black', figsize=(10, 8))
plt.xlabel("Longitude")
plt.ylabel("Latitude")
plt.show()

Custom Native Library Path

db = H2GIS(lib_path="/custom/path/h2gis.so")

Notes

• By default, the native .so, .dll are already included in the package, in the lib folder.