Le lundi 19 mars 2012 03:23:58, Glen Atkins a écrit : > Hi there, > > When getting the properties from the Trace Header of the Seg-Y file the CDP > X (181-184) and CDP Y (185-188) are not included. This first appeared to > be because the CDP X and CDP Y were being used to set the OGRPoint X and Y > but these values are coming from GROUP_ X (81-84) and GROUP_Y (85-88). Is > there a reason why the CDP_X and CDP_Y aren't included?
Well, I don't recall all the details, but when I tried on various sample files available around the web, I found that some used the old seg-y format that only used bytes 1-180 (*) (the other ones being vendor specific), so I prefered to stick to those ones. And I'm not sure how you can distinguish those files that implement the old spec from files that implement the new spec. Ultimatilely , if there's no automated way of figuring that out, this could be done with the help of a configuration option where the user could tell : use CDP instead of GROUP. Could you open a ticket in GDAL trac on that topic with a sample file (you can likely cut it to the first hundreds of kilobytes with an hexadecimal editor so it is reasonable small to attach) where CDP X/Y are available ? Best regards, Even (*) From http://www.seg.org/documents/10161/77915/seg_y_rev1.pdf : """ 7. Data Traces 7.1. Trace Header The SEG Y trace header contains trace attributes, which are defined as two-byte or four-byte, two's complement integers. The values in bytes 1-180 were defined in the 1975 standard and these entries remain unchanged, although clarification and extensions may be supplied where appropriate. Bytes 181-240 were for optional information in the 1975 standard and this has been the main area of conflict between different flavors of SEG Y. This revision defines standard locations in bytes 181-240 for certain values that are needed in modern data processing. """ > > Thanks, > Glen > > > > [cid:mm_corp_emailsig_perth.gif@99c73ceedff042e6be6ce85322d223a5] _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
