I have some PNG images that I want to put on an OpenLayers map using GeoServer as a WMS, and it seems as though the easiest way to do that would be to create an accompanying .pnw file (ESRI world file) for each .png and load them using GeoServer's WorldImage plugin.
I also have the longitude, latitude coordinates of nine points on each rectangular image: {top, middle, bottom} x {left, middle, right}, and I can use five of them to convert pixel x,y into longitude, latitude x',y':
%20x%20%2B%20%5Cleft(%5Cfrac%7Btm_%7Blng%7D%20-%20bm_%7Blng%7D%7D%7Bheight%7D%5Cright)%20y%20%2B%20%5Cleft(mm_%7Blng%7D%20%2B%20%5Cfrac%7Bmr_%7Blng%7D%20-%20ml_%7Blng%7D%7D%7B2%7D%20%2B%20%5Cfrac%7Btm_%7Blng%7D%20-%20bm_%7Blng%7D%7D%7B2%7D%5Cright))
%20x%20%2B%20%5Cleft(%5Cfrac%7Btm_%7Blat%7D%20-%20bm_%7Blat%7D%7D%7Bheight%7D%5Cright)%20y%20%2B%20%5Cleft(mm_%7Blat%7D%20%2B%20%5Cfrac%7Bmr_%7Blat%7D%20-%20ml_%7Blat%7D%7D%7B2%7D%20%2B%20%5Cfrac%7Btm_%7Blat%7D%20-%20bm_%7Blat%7D%7D%7B2%7D%5Cright))
where (mm_lng, mm_lat) is the position of the middle-middle point, (mr_lng, mr_lat) is middle-right, (tm_lng, tm_lat) is top-middle, etc. for the middles of the four sides. This is a linear approximation to the full coordinate transformation, minimizing error at the center of the image.
The World Image format describes an affine transformation in the same way: the six parenthesized terms above can be interpreted as the six lines of the .pnw file (in A, B, C, D, E, F order) if the map units are longitude, latitude coordinates (that is, WGS84 a.k.a. EPSG:4326). The World file Wikipedia page says "World files describing a map on the Universal Transverse Mercator coordinate system (UTM) use these conventions..." and goes on to describe the UTM application, though it also says, "World files do not specify a coordinate system; this information is generally stored somewhere else."
If the result of the .pnw conversion is interpreted as UTM, then I would need to do additional work to transform from WGS84 into UTM, and GeoServer would also need more information to specify which of the 60 UTM zones that the .pnw converts into. I don't see how to provide that information to GeoServer. Am I right in assuming that GeoServer interprets the .pnw-converted coordinates as WGS84?
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I also have the longitude, latitude coordinates of nine points on each rectangular image: {top, middle, bottom} x {left, middle, right}, and I can use five of them to convert pixel x,y into longitude, latitude x',y':
where (mm_lng, mm_lat) is the position of the middle-middle point, (mr_lng, mr_lat) is middle-right, (tm_lng, tm_lat) is top-middle, etc. for the middles of the four sides. This is a linear approximation to the full coordinate transformation, minimizing error at the center of the image.
The World Image format describes an affine transformation in the same way: the six parenthesized terms above can be interpreted as the six lines of the .pnw file (in A, B, C, D, E, F order) if the map units are longitude, latitude coordinates (that is, WGS84 a.k.a. EPSG:4326). The World file Wikipedia page says "World files describing a map on the Universal Transverse Mercator coordinate system (UTM) use these conventions..." and goes on to describe the UTM application, though it also says, "World files do not specify a coordinate system; this information is generally stored somewhere else."
If the result of the .pnw conversion is interpreted as UTM, then I would need to do additional work to transform from WGS84 into UTM, and GeoServer would also need more information to specify which of the 60 UTM zones that the .pnw converts into. I don't see how to provide that information to GeoServer. Am I right in assuming that GeoServer interprets the .pnw-converted coordinates as WGS84?
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