area-splitter 3.0.1
A utility for splitting an AOI into multiple tasks.
Requires Python: >=3.10
Keywords: aoi, field-tm, hot, postgis, split

# Area Splitter

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  <em>A utility for splitting an AOI into multiple tasks.</em>
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---

📖 **Documentation**: <a href="https://hotosm.github.io/fmtm-splitter/" target="_blank">https://hotosm.github.io/fmtm-splitter/</a>

🖥️ **Source Code**: <a href="https://github.com/hotosm/field-tm/blob/main/src/backend/packages/area-splitter" target="_blank">https://github.com/hotosm/field-tm/blob/main/src/backend/packages/area-splitter</a>

---

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This is a program to split polygons into tasks using a variety of
algorithms. It is a class that can be used by other projects, but also
a standalone program. It was originally developed for the
[FMTM](https://github.com/hotosm/fmtm/wiki) project, but then
converted so it can be used by multiple projects.

The class takes GeoJson Polygon as an input, and returns a GeoJson
file Multipolygon of all the task boundaries.

## Installation

```bash
pip install area-splitter
```

> Note Postgis should have SFCGAL enabled:
>
> ```sql
> CREATE EXTENSION IF NOT EXISTS postgis_sfcgal WITH SCHEMA public;
> ```

## Splitting Types

### Split By Square

The default is to split the polygon into squares. The default
dimension is 50 meters, but that is configurable. The outer square are
clipped to the AOI boundary.

### Split By Feature

The split by feature uses highway data extracted from OpenStreetMap,
and uses it to generate non square task boundaries. It can also be
adjusted to use the number of buildings in a task to adjust it's
size.

![Split By Feature](https://github.com/hotosm/fmtm-splitter/blob/main/docs/images/Screenshot%20from%202023-08-06%2018-26-34.png)

### Custom SQL query

It is also possible to supply a custom SQL query to generate the
tasks.

## Usage In Code

- Either the FMTMSplitter class can be used directly, or the wrapper/
  helper functions can be used for splitting.

By square:

```python
import json
from area_splitter.splitter import split_by_square

aoi = json.load("/path/to/file.geojson")

split_features = split_by_square(
    aoi,
    meters=100,
)
```

The FMTM splitter algorithm:

```python
import json
from area_splitter.splitter import split_by_sql

aoi = json.load("/path/to/file.geojson")
osm_extracts = json.load("/path/to/file.geojson")
db = "postgresql://postgres:postgres@localhost/postgres"

split_features = split_by_sql(
    aoi,
    db,
    num_buildings=50,
    osm_extract=osm_extracts,
)
```

### Database Connections

- The db parameter can be a connection string to start a new connection.
- Or an existing database connection can be reused.
- To do this, either the psycopg connection, or a DBAPI connection string
  must be passed:

psycopg example:

```python
import psycopg
from area_splitter.splitter import split_by_sql

db = psycopg.connect("postgresql://postgres:postgres@localhost/postgres")

split_features = split_by_sql(
    aoi,
    db,
    num_buildings=50,
    osm_extract=osm_extracts,
)
```

## Usage Via CLI

Options:

```bash
-h, --help                       show this help message and exit
-v, --verbose                    verbose output
-o OUTFILE, --outfile OUTFILE    Output file from splitting
-m METERS, --meters METERS       Size in meters if using square splitting
-b BOUNDARY, --boundary BOUNDARY Polygon AOI
-s SOURCE, --source SOURCE       Source data, Geojson or PG:[dbname]
-c CUSTOM, --custom CUSTOM       Custom SQL query for database
```

This program splits a Polygon (the Area Of Interest)
The data source for existing data can'be either the data extract
used by the XLSForm, or a postgresql database.

Examples:

```bash
area-splitter -b AOI
area-splitter -v -b AOI -s data.geojson
area-splitter -v -b AOI -s PG:colorado

# Where AOI is the boundary of the project as a polygon
# And OUTFILE is a MultiPolygon output file,which defaults to fmtm.geojson
# The task splitting defaults to squares, 50 meters across
```