Online Historical Map Georeferencer (OHMG)

OHMG is a web application that facilitates public participation in the process of georeferencing and mosaicking historical maps. This is a standalone project that requires an external instance of Titiler to serve the mosaicked layers. See Dependencies below for more about the tech stack.

At present, the system is structured around the Sanborn Map Collection at the Library of Congress (loc.gov/collections/sanborn-maps). More generic ingestion methods are in the works.

• Implementation: oldinsurancemaps.net
• Documentation: about.oldinsurancemaps.net

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Please don't hesitate to open a ticket if you have trouble with the site, find a bug, or have suggestions otherwise.

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Software Details

This is a Django project, with a frontend built (mostly) with Svelte, using OpenLayers for all map interfaces. OpenStreetMap and Mapbox are the basemap sources.

Third-party Django Apps

• Django Ninja - API
• Django Newsletter - Newsletter (optional feature)

External Dependencies

• Postgres/PostGIS
• Celery + RabbitMQ
• GDAL >= 3.5
• TiTiler

Development Installation

Running the application requires a number of components to be installed and configured properly. This aspect of the application is not optimized, but getting it documented is the first step.

Create database

Install Postgres/PostGIS as you like. Once running, create a database like this

psql -U postgres -c "CREATE USER ohmg WITH ENCRYPTED PASSWORD '$DB_PASSWORD'"
psql -U postgres -c "CREATE DATABASE oldinsurancemaps WITH OWNER ohmg;"
psql -U postgres -d oldinsurancemaps -c "CREATE EXTENSION PostGIS;"

See also ./scripts/create_database.sh. You can run this script once you have updated the DATABASE_* variables in .env.

Install Django project

Make virtual env

python3 -m venv env
source env/bin/activate

Install GDAL bindings. These must match exactly the version of GDAL you have on your system, so use this command:

pip install gdal=="`gdal-config --version`.*"

Install the ohmg Python package and dependencies

git clone https://github.com/mradamcox/ohmg && cd ohmg
pip install -e .[dev]

Set environment variables

cp .env.example .env

Initialize database, create admin user

python manage.py migrate
python manage.py createsuperuser

Load all the place objects to create geography scaffolding

python manage.py place import-all

Build frontend

The frontend uses a suite of independently built svelte components.

cd ohmg/frontend/svelte
pnpm install
pnpm run dev

Run Django dev server

You can now run

python manage.py runserver

and view the site at http://localhost:8000.

However, few more components will need to be set up independently before the app will be fully functional. Complete the following sections and then rerun the dev server so that any new .env values will be properly aqcuired.

Rabbit + Celery

In development, RabbitMQ can be run via Docker like so:

docker run --name rabbitmq --hostname my-rabbit \
  -p 5672:5672 \
  -p 15672:15672 \
  -e RABBITMQ_DEFAULT_USER=username \
  -e RABBITMQ_DEFAULT_PASS=password \
  --rm \
  rabbitmq:3-alpine

For convenience, this command is in the following script:

source ./scripts/rabbit_dev.sh

Once RabbitMQ is running, update .env with the RABBITMQ_DEFAULT_USER and RABBITMQ_DEFAULT_PASS credentials you used above when creating the container.

Now you are ready to run Celery in development with:

source ./scripts/celery_dev.sh

TiTiler

TiTiler can also be run via Docker, using a slightly modified version of the official container (it is only modified to include the WMS endpoint extension):

docker run --name titiler \
  -p 8008:8000 \
  -e PORT=8000 \
  -e MOSAIC_STRICT_ZOOM=False \
  -e WORKERS_PER_CORE=1 \
  --rm \
  -it \
  ghcr.io/mradamcox/titiler:0.11.6-ohmg

Or the same command is wrapped in:

source ./scripts/titiler_dev.sh

This will start a container running TiTiler and expose it to localhost:8008.

Make sure you have TITILER_HOST=http://localhost:8008 in .env.

Static file server

During development, a separate HTTP server must be used to supply Titiler with COG endpoints, because the Django dev server does not serve HTTP range requests (more on this here and here). The easiest workaround is to use node's http-server.

From within the repository root (alongside the uploaded directory) run:

npx http-server .

All COGs will now be accessible at http://localhost:8080/uploaded/.

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Make sure you have MEDIA_HOST=http://localhost:8080 in .env. MEDIA_HOST is a prefix that will be prepended to any uploaded media paths that are passed to TiTiler.

In production, you will already be using a webserver for static files so you will not need to use http-server. In this case, remove MEDIA_HOST from .env or set it to ''.

Running Tests

All tests are stored in ohmg/tests. Make sure you have installed dev requirements, then run:

python manage.py test ohmg/tests

To skip the tests that make external calls to the LOC API, use the following command. Keep in mind that coverage numbers will be lower when you skip tests.

python manage.py test ohmg/tests --exclude-tag=loc