Phew. Yes I had a suspician it would not be easy - or small. If I get into
this, then for the moment my GPOS is not differential, but that doesn't
matter for the development. There are some Diff sites up here I could access
though. (America cup ra ra ra does have some benifits)
I already have the GPS output hooked up and logging to a database.
I can see there are lots of impossibilities with hoping to scan any old map,
but suppose I limited these to certain publications such as genuine ocean
charts, and further restricted myself to certain well defined projections.
Do these restrictions bring it a little more within a Do-able definition?
Anyway, thanks for the encouragement - I'l take a look at the web sites.
Cheers,
Tony.
-----Original Message-----
From: Phil Scadden <[EMAIL PROTECTED]>
To: Multiple recipients of list delphi <[EMAIL PROTECTED]>
Date: Wednesday, 6 October 1999 9:11 AM
Subject: Re: [DUG]: Mapping and GPS
> I am interested in taking a paper map, and scanning it in, then writing
> some picture clean up and documenting stuff. I also need to figure out how
to
> map the lat long coordinates on to the image, which map projections to use
etc
> Tec. I suppose I will then store the images in an IB database, for later
> retrieval. The next step is to bring in the NMEA message from the GPS and
> plot the real-time coordinates on the picture. Hopefully this part is
> straightforward. It is the picture conversion clean up and coordinate
> mapping that has me stymied.
Boy, this is a real job - you realise you can buy the software for a
fraction of
what it is going to cost you in time??
Where to start. Your GPS is the first question. Assume you are NOT doing
differential
GPS in which case your accuracy would only be 100m. You also have to
worry about datum. A GPS's "natural" coordinate frame is to report LAT/LONG
on
the WGS84 datum. In contrast, maps of NZ will have LAT/LONG on the NZGD49
datum which is about 200m different. More modern GPS can do datum
translation
but you need to watch whether they use a 3 parameter or 7 parameter. 3
parameter
conversion are only within 15m but that is good enough I guess unless you
are
doing differential GPS.
Coordinate projection is a massive topic. Snyder's "Map Projections -
a working manual" is the "bible" and it lives permanently in my office. I
normally
have vast array of tools including Arcinfo,Arcview and Mapinfo GIS systems
to
handle coordinate projection but I HAVE written delphi code to handle some
of projections and datum transformations as well. I would be interested in
developing
this further as have an outline for a projection class.
However, you may well be advised to look at the TGlobe component from
Graham Knight ([EMAIL PROTECTED] - webpage easily findable). Not
cheap though. He doesnt have a huge range of projections but does do common
one.
If you have C++, then should search net for the Proj.4 library which is
extremely
comprehensive.
----------------------------------------------------------
Phil Scadden, Institute of Geological and Nuclear Sciences
PO Box 30368, Lower Hutt, New Zealand
Ph +64 4 5704821, fax +64 4 5704603
---------------------------------------------------------------------------
New Zealand Delphi Users group - Delphi List - [EMAIL PROTECTED]
Website: http://www.delphi.org.nz
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New Zealand Delphi Users group - Delphi List - [EMAIL PROTECTED]
Website: http://www.delphi.org.nz
