[Gdal-dev] OGR Georeference

[Rob McCulley]

I finally managed to talk to the data provider.  It is a "local" coordinate system per file.  It looks like I need to warp each file.  Any way to do this using ogr?

Thanks,
Rob

-----Original Message-----
From: Brent Fraser [mailto:bfraser at geoanalytic.com]
Sent: Wednesday, April 19, 2006 11:43 AM
To: Rob McCulley; Gdal (E-mail)
Subject: Re: [Gdal-dev] OGR Georeference


Rob,

Hmm.  A twp is typically about 6 miles / 10 km wide, so I'd guess the units
are kilometers.  If the twp lines are vertical and horizontal in every file,
I'd guess they are each in their own "local" coordinate system (hope not
because that would mean you would have to warp each file).  If the twp lines
in some of the files are rotated slightly (10 degrees or so) then they may
be projected.

The most likely projections are:

UTM - 6 degree zones
10TM - a 10 degree zone for all of Alberta
3TM - 3 degree zones

AltaLIS has a document (global_origin.doc) included with their product
samples(http://www.altalis.com/productsandsamples/Samples/BF_DWG.zip)
listing the various projections (with scale factors, central meridians and
DGN Global Origins).  Of course this is really only for AltaLIS data, but it
may be valid for your data too depending on it's source...

Brent Fraser
GeoAnalytic Inc
Calgary, Alberta, Canada


----- Original Message ----- 
From: "Rob McCulley" <RMcCulley at county24.com>
To: "Gdal (E-mail)" <gdal-dev at lists.maptools.org>
Sent: Wednesday, April 19, 2006 11:01 AM
Subject: RE: [Gdal-dev] OGR Georeference


> After a closer inspection of the files, it appears that there are two
types.  The first that I had seen earlier, the center of each file is 0,0
and I have no idea what the units are, something large.  The x range across
the entire file is -5.5 to 5.5, a
> nd that corresponds to a single township.  My township file was created
from the 2005 ATSCOR file available from Altalis, these are almost
definately something older.
>
> The second set of files are in some form of UTM projection.  I have no
info on them other than what was written on the CD: NAD83 - UTM - Metres.
These are files of pipelines in Alberta, and I've heard that Alberta T & U
had a custom projection that the
> y used, but I don't know the specs on it at all.
>
> I've tried setting them as 10TM, but that wasn't right.
>
> Thanks,
> Rob
>
> -----Original Message-----
> From: Brent Fraser [mailto:bfraser at geoanalytic.com]
> Sent: Wednesday, April 19, 2006 9:24 AM
> To: Rob McCulley; Gdal (E-mail)
> Subject: Re: [Gdal-dev] OGR Georeference
>
>
> Rob,
>
>   This could get tricky.   Is it just a georeferencing (i.e offset)
problem
> or a map projection problem as well?   Do you know the map projection of
the
> DGNs?  And the units (meters, feet, etc)?    You may need to apply a scale
> to get the right units for your resulting shapefile, and possibly project
> (or warp!) the DGN data into a world coordinate system.
>
>   And there could be some issues with the Township coordinates.  The
Alberta
> government (and others) has issued different versions of the positions
over
> the years so the relative positions in the DGNs might not match your
> Township shapefile very well.
>
> Brent Fraser
> GeoAnalytic Inc
> Calgary, Alberta, Canada
>
>
> ----- Original Message ----- 
> From: "Rob McCulley" <RMcCulley at county24.com>
> To: "Gdal (E-mail)" <gdal-dev at lists.maptools.org>
> Sent: Wednesday, April 19, 2006 9:08 AM
> Subject: [Gdal-dev] OGR Georeference
>
>
> > Hi All,
> >
> > I've got a bunch of .dgn files that are not georeferenced at all (i.e.
the
> center of each file is (0,0)).  Each file corresponds exactly to one
> township, and I've got a shapefile with all of the townships.  In addition
> to the survey information, each fi
> > le contains four points which are the four corners of the township.  The
> file name of each .dgn file corresponds with the township represented.
> >
> > I've got a python script that opens the .dgn file, selects the
appropriate
> township from the shapefile depending on the .dgn title, opens a shapefile
> to output to, and then I'm stumped.  Is it possible to use ogr to
> georeference this stuff?  I've looked
> >  at using a ogr::CoordinateTransform, but I can't figure out what to put
> as the source srs.
> >
> > I know Arcview can do what I'm looking for, but it is a tedious manual
> process called Spatial Adjustment.  I've got 342 .dgn files to work
through,
> so I'm looking to automate the process.
> >
> > Thanks,
> > Rob McCulley
> > GIS Coordinator
> > County of Vermilion River No. 24
> > (780) 846-2244
> > www.vermilion-river.ab.ca
> >
> > _______________________________________________
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> > Gdal-dev at lists.maptools.org
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>
>
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