ckanext-malmo

Customizations for the City of Malmo CKAN instance.

Requirements

• CKAN 2.10+ (tested on 2.11)

DWG Preview

This extension exposes a binary preview action at:

/api/3/action/convert_dwg?id=<resource-id>

The preview flow is:

1. stage the DWG resource into a temporary file
2. convert DWG -> DXF with ODA File Converter
3. render DXF -> PNG with ezdxf and matplotlib
4. cache the generated PNG by resource id + file hash
5. return the PNG directly from the CKAN endpoint

Important runtime requirements:

• ODA File Converter must be installed and available on PATH
• xvfb is used automatically when xvfb-run is available
• Python rendering dependencies must be installed in the CKAN runtime

Python runtime dependencies:

• ezdxf
• matplotlib

System/runtime dependencies:

• ODA File Converter Linux asset (.AppImage or .deb)
• xvfb

DWG Preview Configuration

The DWG preview pipeline supports these CKAN config settings:

• ckanext.malmo.dwg_preview_timeout Conversion timeout in seconds. Default: 45.

• ckanext.malmo.dwg_preview_download_timeout Download timeout in seconds for remote DWG resources. Default: 30.

• ckanext.malmo.dwg_preview_max_download_bytes Maximum DWG download size in bytes. Default: 104857600.

• ckanext.malmo.dwg_preview_oda_executable Absolute path or executable name for ODA File Converter. Default: ODAFileConverter.

• ckanext.malmo.dwg_preview_oda_output_version DXF target version passed to ODA File Converter. Default: ACAD2018.

• ckanext.malmo.dwg_preview_xvfb_screen Screen configuration passed to xvfb-run when launching ODA File Converter in headless Docker environments. Default: -screen 0 1600x1200x24.

• ckanext.malmo.dwg_preview_render_margin Extra margin applied around rendered geometry. Default: 0.05.

• ckanext.malmo.dwg_preview_image_width Output preview width in pixels. Default: 1600.

• ckanext.malmo.dwg_preview_image_height Output preview height in pixels. Default: 1200.

• ckanext.malmo.dwg_preview_min_preview_bytes Minimum byte size for accepting a generated preview. Default: 1024.

• ckanext.malmo.dwg_preview_cache_dir Directory used for cached PNG previews. Default: system temporary directory + ckan-dwg-preview-cache.

Docker Setup

In the local development Docker setup:

• ODA File Converter is installed during image build
• the local src/ckanext-malmo extension is installed at container startup from the mounted workspace
• xvfb is installed for headless ODA execution

Optional local ODA asset override directory:

ckan/vendor/oda/

Supported local asset formats:

• .AppImage
• .deb

Installation

To install ckanext-malmo:

1. Install the extension in your environment.
2. Install ODA File Converter and make sure ODAFileConverter is available in the runtime environment.
3. Add malmo to the ckan.plugins setting in your CKAN configuration file.