Display of a WMS service containing a PNG24 format file appears without transparent background

Description

When attempting to publish a WMS (web map service) containing a PNG24 format file, the service displays without a transparent background. Instead, the WMS service is displayed with a white background similar to the behavior of a JPG format image file. The following image shows a WMS displayed with a white background.

Cause

This is a known limitation. As per the Open Geospatial Consortium (OGC) WMS specification, a GetMap request made without the TRANSPARENT parameter in the URL displays a PNG24 file format with the TRANSPARENT parameter set to FALSE by default. The following image shows a URL segment where the TRANSPARENCY parameter is intentionally set to FALSE.

Solution or Workaround

The GetMap request must include the TRANSPARENT=TRUE parameter set in the URL of the map service. The following image demonstrates the URL with the TRANSPARENT parameter set to TRUE.