QGIS COG Tiler

Process to take QGIS project through to Cloud-Optimised GeoTIFF (COG) creating a COG raster that acts like a styled raster tile.

The method is still in development.

Summary

A scripted method to leverage QGIS and pyQGIS to export styled images at each zoom scale of interest, then convert those images into a single COG format.

The basic premise is to create a QGIS project with data that employs styling rules for each zoom level. This includes changes in line widths, blending, turning data on and off, etc. With the QGIS project in place, we then export raw tif images for each zoom scale at varying resolutions. The images are coverted to GeoTiff and built using an overview structure, with the lowest resolution being the root. The root image, with overviews, is then converted to a COG. The COG is a single Tif image, with overviews internally tiled like a raster tile. This COG can then be used in a web client like a raster tile.

This method requires a Tile Matrix. For this project, resolutions and scales are set following LINZ map tile standards.

Method

Base process is as follows:

1. Develop QGIS project
2. Build in zoom rules for scales
3. "Export as Image" based on scale
4. Images are built with an overview structure, with the lowest scale being the base of the overviews
5. Combine images into COG.
6. Upload COG to S3 and consume via webviewer

Open QGIS project

QGIS editor and tiler can be run from Docker:

docker pull dragonflyscience/qgis-builds:3.22.12.ltr.20221109

or users can build the QGIS docker using:

make docker

Launch QGIS editor:

make qgis

Launch Tiler

make tiler

Export Images

Inside tiler run:

make QGISPROJECT=[YOUR QGIS PROJECT PATH HERE].qgz SCALES=YOUR,SCALES,HERE image-exports

Example:

make QGISPROJECT=qgis/full-nz.qgz.qgz SCALES=32000000,16000000,8000000 image-exports

Create VRTs and COGs

After images are created:

make SCALES=YOUR,SCALES,HERE create-cog

Example:

make QGISPROJECTNAME=full-nz SCALES=32000000,16000000,8000000 create-cog

On the Web

COGs may be loaded to S3 for use in Openlayers.

See: https://github.com/dragonfly-science/qgis-cog-tiler/tree/website/web-docs for setting up Openlayers

Launch Web Editing

Web components built using OpenLayers v6

Load website for editing:

npm start

Build project and move build to proper location for Git to use:

bash utils/build-move.py