On 18/09/18 23:55, Nick Griffiths wrote: >> So perhaps this is an issue with the AsciiGridsImageReader? > > I think I might have found something with the asciigridsimagereader. > It looks like it's to do with the tile marker cache being used to find a > good spot to start seeking from. > > 1) In the case of freshly created grid, the tile marker cache is empty, > and so we are forced to seek through the entire file to find where to > start looking, and the reader returns the right set of values. > > 2) In the case of an adjacent tile look up, the tile marker cache gives > us an exact match and correctly lines up the input stream at the right > position. The reader returns the right set of values. > > But in the case of the nearest lower key found in the marker cache, > things can go awry. I can see that the skipping code in this instance > seems to put is in at the wrong position. Given that case 1) works, > which uses the same skipping code, I must assume that the marker cache > is returning the wrong result here (possibly either the wrong sample > position or the wrong seek position?) or is being misused in a way that > results in derived results being poisoned?
Eureka! So it's an off by one error when reusing those cached skip positions. https://paste.dollyfish.net.nz/540649 This diff seems to fix it for my particular asc file - I don't quite understand why it works, and whether it's particular to the layout of this particular file or something else. Anyway, I've got to the bottom of most of it, more to come tomorrow. _______________________________________________ GeoTools-GT2-Users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
