From Twitter announcement we learned that bicubic interpolation has now been enabled as an option (build dated 24 February). This is very welcome news.
The setting is in a good place, on the Display tab of the Options sheet for a raster layer. The former option "Anti-alias pixels (interpolate)" is replaced by a drop-down box with three options: nearest neighbour, bilinear, bicubic. As I read it, nearest neighbour is equivalent to the previous "off" setting, bilinear is equivalent to the previous "on" setting, and bicubic is new. So far so good.
However, I'm getting corruption of both display and resampled exports on every image raster I've tried so far. Horizontal interpolation seems to be out of sync from row to row. (I've attached an example.) I don't know whether the problem is also occurring with DEM rasters (I haven't tested well enough yet).
For DEMs (with shading enabled) a different sort of corruption: with the bicubic method, no shading or visible contrast on zooming in, but a featureless black or grey. Corrected by selecting biliear instead.
The Twitter post was premature as the bicubic support is not complete in an official build. It doesn't work at all for elevation files and still has some issues for imagery. Hopefully it will be completed in a couple of days in a new build.
I've got the bicubic resampling working for non-elevation files. I have placed a new build at http://www.globalmapper.com/global_mapper11.zip with the change for you to try. Simply download that file and extract the contents into your existing v11.xx installation folder to give it a try. If you are using the 64-bit v11 version there is a new build at http://www.globalmapper.com/global_mapper11_64bit.zip .
Hopefully I can get it working for elevation layers in a day or two.
Thanks,
The bicubic resampling should now work for elevation layers as well. I have placed a new build at http://www.globalmapper.com/global_mapper11.zip with the change for you to try. Simply download that file and extract the contents into your existing v11.xx installation folder to give it a try. If you are using the 64-bit version, there is a new build available at http://www.globalmapper.com/global_mapper11_64bit.zip .
Not much difference to notice yet, I think, for sampling down (subsampling). Maybe this is more difficult than just introducing bicubic interpolation. Or perhaps it's just that the radius or decay factor for the interpolation function (if that makes any sense) can be tweaked to a degree.
I've zipped up a Global Mapper project ready to send. (I didn't use a package file as it would introduce lossy compression. It's important to show the original in this case.)
Can I send the zip file to you Mike? It's about 155 MB, close to the stated limit for zip attachments. My first attemtp to attach it failed after a few minutes.
These project contains 4 layers:
"10mpx original" is one of our cartographic textures at it original resolution of 10 metres per pixel.
"40mpx GM bilinear" is the original texture, resampled in Global Mapper to 40 metres per pixel with bilinear resampling set.
"40mpx GM bicubic" is the same, resampled in Global Mapper to 40 metres per pixel, this time with bicubic resampling set.
"40mpx PhS bicubic" is the original texture, resampled in Photoshop CS4 to 40 metres per pixel using the bicubic resampling method.
The GM methods do not do well at preserving the continuity of local detail, which ends up excessively pixellated. This is most noticeable for small linear features such as streams or hedgerows. (Bilinear and bicubic produce very similar results; bicubic introduces slightly greater contrast between adjacent pixels.)
The Photoshop method does much better. The continuity of local detail is visibly preserved despite subsampling.
I wonder how close Global Mapper can get, in principle, to the quality the Photoshop engineers have achieved.
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Bicubic resampling
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