How to optimise raster image display in OpenCPN

OpenCPN is powerful, but its raster image clarity isn’t always the best. The good news: it’s usually just a matter of adjusting the settings.

 1. Check your chart scale

If a chart looks blurry or “blocky,” it’s often because a very small-scale chart is being viewed at too high a zoom level. In these cases, OpenCPN should instead be displaying a more detailed, larger-scale chart.

2. Adjust display settings

  • Go to Tools (spanner icon) → Display → Advanced

  • Move the top slider fully to the right (+5)

  • Ensure the checkbox for Use Accelerated Graphics (OpenGL) is ticked

These adjustments help larger-scale charts appear sooner when zooming in, while OpenGL smooths out the grainy effect.

3. Enjoy full detail

With these settings applied, your Unified Charts should display at their best — often right down to pontoon level — making navigation clearer and more precise.

This guide was first published on 28 February 2019

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