We have recently received orthoimagery tiles for my county. The county is a series of islands and the imagery only covers the islands. Thus we have data gaps where there is only water. In past projects we've created a mosaic by filling in the gaps using a solid blue color that somewhat resembles the median color of the water in the tiles near the shorelines. It worked pretty well in the past, but with this project I'm finding that no single color is working best. Is there a method I can use to make the transition from imagery edge to a solid color more aesthetically pleasing?

  • "pleasing" is going to be at least a bit subjective. What is the goal of the output? That is, what will you use it for, and what will you not use it for? – BradHards Nov 10 '13 at 6:27
  • Hi Brad. My goal is to use the imagery as a base map for web applications. So anything that eases the edge transition on the waters near the shoreline. I've also been considering a rounded buffer of the shorelines to clip the imagery to in order to get rid of the sharper tile edges and corners. – nickpeihl Nov 10 '13 at 16:35

As BradHards noted, "pleasing" is subjective. That being said, two methods come to mind:

(1) Create a new constant raster, erase the islands (assuming you have a vector layer for their boundaries (if not, create one)), and calculate euclidean distance away from the island shores. ESRI has a white paper outlining this method here, although the general idea would work in any GIS program: http://support.esri.com/en/knowledgebase/whitepapers/view/productid/39/metaid/975

(2) Add a vector ocean mask and erase an area (as above) where each island lies. Then, export a high resolution map to Photoshop or a graphics program of your choice. Use the clone tool to copy the near-shore water and work outwards from there. Gradually fading to the solid vector layer.

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