[Gdal-dev] OGR Georeference

[Brent Fraser]

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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