Update etl/migrations docs with a little more on prerequisites

etl/README.md

@@ -8,9 +8,41 @@ for Colouring London:
 
 ## Prerequisites
 
+Install PostgreSQL and create a database for colouringlondon, with a database
+user that can connect to it. The [PostgreSQL
+documentation](https://www.postgresql.org/docs/12/tutorial-start.html) covers
+installation and getting started.
+
+Install the [PostGIS extension](https://postgis.net/).
+
+Connect to the colouringlondon database and add the PostGIS, pgcrypto and
+pg_trgm extensions:
+
+```sql
+create extension postgis;
+create extension pgcrypto;
+create extension pg_trgm;
+```
+
+Create the core database tables:
+
+```bash
+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.
+
+Install GNU parallel, this is used to speed up loading bulk data.
+
+
+## Process and load Ordance Survey data
+
 Before running any of these scripts, you will need the OS data for your area of
 interest. AddressBase and MasterMap are available directly from [Ordnance
-Survey](https://www.ordnancesurvey.co.uk/).
+Survey](https://www.ordnancesurvey.co.uk/). The alternative setup below uses
+OpenStreetMap.
 
 The scripts should be run in the following order:
 
@@ -32,6 +64,10 @@ load_uprns.py ./addressbase_dir
 psql < ../migrations/003.index-buildings.sql
 ```
 
+## Alternative, using OpenStreetMap
+
+This uses the [osmnx](https://github.com/gboeing/osmnx) python package to get OpenStreetMap data. You will need python and osmnx to run `get_test_polygons.py`.
+
 To help test the Colouring London application, `get_test_polygons.py` will attempt to save a
 small (1.5km²) extract from OpenStreetMap to a format suitable for loading to the database.
 
@@ -39,13 +75,17 @@ In this case, run:
 
 ```bash
 # download test data
-get_test_polygons.py
+python get_test_polygons.py
 # load all building outlines
-load_geometries.sh ./test_data_dir
+./load_geometries.sh ./
 # index geometries (should be faster after loading)
-psql < ../migrations/002.index-geometries.sql
+psql < ../migrations/002.index-geometries.up.sql
 # create a building record per outline
-create_building_records.sh
+./create_building_records.sh
 # index building records
-psql < ../migrations/002.index-buildings.sql
+psql < ../migrations/003.index-buildings.up.sql
 ```
+
+## Finally
+
+Run the remaining migrations in `../migrations` to create the rest of the database structure.

migrations/README.md

@@ -8,6 +8,7 @@ $ psql "host={hostname} user={username} port={port} sslmode=require dbname=postg
 > \c colouringlondon
 > create extension postgis;
 > create extension pgcrypto;
+> create extension pg_trgm;
 > \q
 ```