Martin,
I may be misunderstanding how the API works (I'm not actually using it myself), but if someone wants to parse a given layer of the OS MasterMap vector data that is divided into chunks they can't use fixed field numbers, because the field order varies between chunks. For example, suppose I want to only extract the 'physicalPresence' field from the 'TopographicArea' layer. Using your current proposed API I would have to sometimes specify to extract field 10 and sometimes to extract field 11, depending on which chunk I'm reading. This CAN be accommodated of course (although it's rather fiddly), but the problem disappears if field names are used, as field names don't change between chunks. Regards, Jez -----Original Message----- From: Martin Dobias [mailto:[email protected]] Sent: Wednesday 21 July 2010 13:24 To: Jez Walters Cc: [email protected] Subject: Re: [gdal-dev] RFC 29: OGR Set Desired Fields On Wed, Jul 21, 2010 at 1:36 PM, Jez Walters <[email protected]> wrote: > Although I take your point about the interface not affecting ogr2ogr, surely > the potential speed boost is worth extending to this utility too - or would > that be a separate ticket? I for one would welcome improving the performance > of ogr2ogr using the approach you have suggested - when I launch the current > trunk development version of ogr2ogr from VBScript it gets stuck in an > infinite loop trying to process a 5x5km vector data chunk. ogr2ogr could probably use the API when "-select" option is used - to ignore fields which are not being requested. Any other performance improvements are unrelated to this RFC. > This issue aside, won't the fact that field names are constant but field > numbers are not in the OS MasterMap vector data present problems for those > that wish to programmatically parse the OS GML using your interface? AFAIK once a layer gets open, the indexes of fields for this layer stay fixed. Regards Martin The information transmitted is intended only for the person or entity to which it is addressed and may contain confidential and/or privileged material. If you are not the addressee, any disclosure, reproduction, copying, distribution, or other dissemination or use of this communication is strictly prohibited. If you have received this transmission in error please notify the sender immediately and then delete this email. Any representations or commitments expressed in this email are subject to contract. This message has been scanned for viruses and dangerous content. However, it is essential that the recipient also checks this message using commercially available mail scanning and anti-virus software. IPL Information Processing Limited accepts no liability for any loss or damage resulting from any virus or other dangerous content in this message. IPL Information Processing Limited is registered in England and Wales under company registration number 1418818. Registration took place at Cardiff on 10 May 1979. IPL Information Processing Limited's registered office and normal place of business is Eveleigh House, Grove Street, Bath, BA1 5LR, United Kingdom. IPL is also registered for Value Added Tax (VAT) under registration number GB 601 2931 83. _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
