[gdal-dev] Re: Puzzling results from gdalinfo with BSB nautical charts

[Jack Kirkpatrick]

Chris.Barker <Chris.Barker <at> noaa.gov> writes:

> 
> Even Rouault wrote:
> > But I've no idea if there are BSB datasets that are not NAD83 or WGS84. In 
> > which case, the BSB driver would have to be improved to parse the 
appropriate 
> > line.
> 
> If anyone opens up that code, it would be great if they could do a bit 
> more -- BSB defines the projection completely( At least I think it 
> does), in addition to providing the GRPs. It would be nice if that 
> information was not lost.
> 
> What I don't know, is how GDAL can/should deal with having both GRPs and 
> complete projection information.
> 
> Otherwise, it should be a fairly simple matter of parsing the text header.
> 
> -Chris
> 


Chris,

I have been googling around this issue trying to establish if there are in fact 
BSB charts published with "non-WGS84 compatible" datums. 

------------------------

I found the email address of a Kirk Waters in documentation associated with the 
freely available NOAA BSB reprojector (I used xxxkwaters at csc.noaa.gov but he 
replied on xxxKirk.Waters at noaa.gov - the leading xxx I have added in the hope 
it will avoid any spamming) and asked him:

Kirk,
 
I came across your email address while googling a problem I have - you could 
click on the following URL if you would like all the gory detail:
 
http://thread.gmane.org/gmane.comp.gis.gdal.devel/17921
 
Essentially I would be interested in knowing if, to your knowledge, there are 
any BSB charts published that use datums that are not WGS84 or near enough 
to "WGS84 compatible" (e.g. NAD83).
 
Thanking you in anticipation...

------------------------

Kirk's response was (and I hope he doesn't object to my forwarding it):

Jack,
I haven't actually seen one that wasn't NAD83 or WGS84.  Those two are 
only different by about 2 meters, so for most purposes they are the same 
(but not all purposes).  When I wrote the chart reprojector I was only 
looking at NOAA charts and it is likely I did the same thing as the gdal 
utility.  It may well be that the early spec I wrote to had NAD83 and 
WGS84 as the only choices (I'd have to do some digging for the specs at 
work).
It's been a few years since I've looked at the gdal utility for BSB.  I 
know it came out after what I made and they didn't have the luxury of 
having the specification, so they had to guess a few things about the 
header.  At the time there were a couple wrong guesses, but I can't 
remember if they were things that mattered.  I suspect if they did 
matter, they have been fixed by now.

Kirk

------------------------

Seems to me that as you and Kirk work for the same organisation it might make 
sense for you and he to discuss the matter - maybe with a view to supplying 
Frank and co with a copy of the BSB header spec.

I know there were a few copyright issues floating around at one stage that 
Frank has documented elsewhere but maybe these have faded with the passage of 
time. It seems somewhat incongruous that NOAA makes freely available a BSB 
reprojector but an open source project such as GDAL can't get a copy of the 
spec.

If Frank and co were given the spec maybe they would be encouraged to tidy the 
issue up.

Regards...