# Extract, transform and load

The scripts in this directory are used to extract, transform and load (ETL) the core datasets for Colouring London. This README acts as a guide for setting up the Colouring London database with these datasets and updating it.

# Contents

- :arrow_down: [Downloading Ordnance Survey data](#arrow_down-downloading-ordnance-survey-data)
- :penguin: [Making data available to Ubuntu](#penguin-making-data-available-to-ubuntu)
- :new_moon: [Creating a Colouring London database from scratch](#new_moon-creating-a-colouring-london-database-from-scratch)
- :full_moon: [Updating the Colouring London database with new OS data](#full_moon-updating-the-colouring-london-database-with-new-os-data)

# :arrow_down: Downloading Ordnance Survey data

The building geometries are sourced from Ordnance Survey (OS) MasterMap (Topography Layer). We also make use of OS Open TOID data which proves access to a generalised location for those geometries.

## Downloading MasterMap data

1. Sign up for the Ordnance Survey [Data Exploration License](https://www.ordnancesurvey.co.uk/business-government/licensing-agreements/data-exploration-sign-up). You should receive an e-mail with a link to log in to the platform (this could take  up to a week).
2. Navigate to https://orders.ordnancesurvey.co.uk/orders and click the button for: ✏️ Order. From here you should be able to click another button to add a product.
3. Drop a rectangle or Polygon over London and make the following selections, clicking the "Add to basket" button for each:

![](screenshot/MasterMap.png)
<p></p>

4. You should be then able to check out your basket and download the files. Note: there may be multiple `.zip` files to download for MasterMap due to the size of the dataset.
6. Unzip the MasterMap `.zip` files and move all the `.gz` files from each to a single folder in a convenient location. We will use this folder in later steps.

# :new_moon: Creating a Colouring London database from scratch

## Prerequisites

You should already have set up PostgreSQL and created a database in an Ubuntu environment. Make sure to create environment variables to use `psql` if you haven't already:

```bash
export PGPASSWORD=<pgpassword>
export PGUSER=<username>
export PGHOST=localhost
export PGDATABASE=<colouringlondondb>
```

Create the core database tables:

```bash
cd ~/colouring-london
psql < migrations/001.core.up.sql
```

There is some performance benefit to creating indexes after bulk loading data.
Otherwise, it's fine to run all the migrations at this point and skip the index
creation steps below.

You should already have installed GNU parallel, which is used to speed up loading bulk data.

## Processing and loading Ordnance Survey data

Move into the `etl` directory and set execute permission on all scripts.

```bash
cd ~/colouring-london/etl
chmod +x *.sh
```

Extract the MasterMap data (this step could take a while).

```bash
sudo ./extract_mastermap.sh /path/to/mastermap_dir
```

Filter MasterMap 'building' polygons.

```bash
sudo ./filter_transform_mastermap_for_loading.sh /path/to/mastermap_dir
```

Load all building outlines. Note: you should ensure that `mastermap_dir` has permissions that will allow the linux `find` command to work without using sudo.

```bash
./load_geometries.sh /path/to/mastermap_dir
```

Index geometries.

```bash
psql < ../migrations/002.index-geometries.up.sql
```

Drop building outlines outside London boundary.

```bash
cd ~/colouring-london/app/public/geometries
ogr2ogr -t_srs EPSG:3857 -f "ESRI Shapefile" boundary.shp boundary-detailed.geojson
cd ~/colouring-london/etl/
./drop_outside_limit.sh ~/colouring-london/app/public/geometries/boundary.shp
```

Create a building record per outline.

```bash
./create_building_records.sh
```

Run the remaining migrations in `../migrations` to create the rest of the database structure.

```bash
ls ~/colouring-london/migrations/*.up.sql 2>/dev/null | while read -r migration; do psql < $migration; done;
```

# :full_moon: Updating the Colouring London database with new OS data

In the Ubuntu environment where the database exists, set up environment variable to make the following steps simpler.
```bash
export PGPASSWORD=<pgpassword>
export PGUSER=<username>
export PGHOST=localhost
export PGDATABASE=<colouringlondondb>
```

Move into the `etl` directory and set execute permission on all scripts.

```bash
cd ~/colouring-london/etl
chmod +x *.sh
```

Extract the new MasterMap data (this step could take a while).

```bash
sudo ./extract_mastermap.sh /path/to/mastermap_dir
```

Filter MasterMap 'building' polygons.

```bash
sudo ./filter_transform_mastermap_for_loading.sh /path/to/mastermap_dir
```

Load all new building outlines. This step will only add geometries that are not already present (based on the `TOID`). Note: you should ensure that `mastermap_dir` has permissions that will allow the linux `find` command to work without using sudo.

```bash
./load_new_geometries.sh /path/to/mastermap_dir
```

Drop building outlines outside London boundary.

```bash
cd ~/colouring-london/app/public/geometries
ogr2ogr -t_srs EPSG:3857 -f "ESRI Shapefile" boundary.shp boundary-detailed.geojson
cd ~/colouring-london/etl/
./drop_outside_limit.sh ~/colouring-london/app/public/geometries/boundary.shp
```

Create building record to match each new geometry (TOID) that doesn't already have a linked building.

```bash
./create_new_building_records.sh 
```

Mark TOIDs not present in the update as demolished.

```bash
./mark_demolitions.sh
```