> Ha! Pleased to meet you. So I don't have to convince you of > stellarium's merits. Thanks for the nice software!
:) Thanks. >> http://porpoisehead.net/images/dss_blend_needed.jpg > > Okay, I see now. What sort of distortion is that? It's a bit complicated, and I don't have all the details, so this description might need to be amended if we need to probe into it in more detail. The DSS tiles are split from large, high resolution photographic plates which are themselves subject to distortions due to the optical properties of the telescope used. I can find a detailed description of the distortion if necessary. It's not a standard barrel distortion though. We chop these plate images into slightly overlapping tiles, run them though some programs which remove the plate specific distortion preparing them for the toast projection method: http://www.worldwidetelescope.org/docs/worldwidetelescopeprojectionreference.html Stellarium reads these tiles, knows about the toast projection and translates this into sky coordinates "unwrapping" the tiles onto the sky. Stellarium itself can project the curved sky onto the screen with multiple methods, but this is not important for processing the images. > It looks like the > tiles were brighter towards one corner, with some colour variation > from blue to reddish thrown in. Hugin's notion of brightness > variations are that they are a function of radial distance from a > point, so it can deal with vignetting, but the data at hand look like > as if there's maybe also a gradient on them, which hugin couldn't deal > with. Mind you, if it can be conceived of as vignetting, it should be > possible, and it doesn't matter if the vignetting is off-center. As > far as the chromatic variations are concerned, I'm more pessimistic. There are many factors here. Vignetting is probably a large part of it. Individual tiles may come from close to or far from the optical axis of the telescope which was used to create them, so if it's possible to have the center of the vignetting compensation be far outside of an individual image, that might work well. The exact way the vignetting affects the image is probably not quite the same as with normal camera lenses, but I dare say it is well documented and details can be found if necessary. The original plates were taken over a long period of time, so there will be plate-to-plate variations which are much harder to compensate for - atmospheric conditions when an individual plate was exposed such as dust and water vapor in the atmosphere, altitude angle and so on, scattering of light from bright objects such as the moon and planets and so on. >> This image shows some of the Northern hemisphere with tiles we have >> imported so far. These are only the lowest resolution tiles... as one >> zooms in, higher resolution tiles are loaded (several per visible tile >> at this lowest resolution. This is somehow similar to how projects >> like OpenStreetMap have multires image sets). > > ... or Microsoft's HD View. > > Are the images in a place where one could access them, to have a more > in-depth view - and also at the metadata to see how feasible it would > be to take them in en masse and run them through some batch job? If I > could get my hands on some of them, I'd gladly see what I can do to > help you. The images can be downloaded, but it's hard to know which ones are adjacent at a given resolution. I will try to research this. Matthew -- You received this message because you are subscribed to the Google Groups "Hugin and other free panoramic software" group. A list of frequently asked questions is available at: http://wiki.panotools.org/Hugin_FAQ To post to this group, send email to hugin-ptx@googlegroups.com To unsubscribe from this group, send email to hugin-ptx+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/hugin-ptx
