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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | GISList: GeoTIFF Headers |
| Date: |
04/11/2003 08:40:00 AM |
| From: |
Andy Morris |
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Sarah,
I read the ESRI support pages you listed and they were informative, but I w=
ould like to dig a little deeper and see if you have any further insight in=
to GeoTIFFs. The second document listed states that "ArcGIS does not provi=
de a mechanism to alter the GeoTIFF tags that control the internal georefer=
encing of TIFF images." However, when I define spatial reference informati=
on for a GeoTIFF a temporary file is created that grows in size until it ma=
tches the original GeoTIFF image size then it is removed and the original G=
eoTIFF's modified date/time changes and the file is 1 KB larger than it was=
before I defined the spatial reference information. I can then delete the=
corresponding .aux file and still list the projection information through =
ArcCatalog-->properties for that image. At no point is there a world file =
created. This would appear to mean that you don't have to do the image -->=
grid then grid --> image manipulation after all. I dug this deep because =
we are producing GeoTiffs for the USGS and the header contains some custom =
information that I want to preserve after metadata creation that needs spat=
ial reference information. Anybody really know what is happening?
Cheers,=20
Andy Morris=20
GIS Supervisor=20
Merrick & Company=20
andy.morris@merrick.com <mailto:andy.morris@merrick.com>=20
Original reply:
Monica,
One possible source of your problem: ArcView 8.x does not read coordinate=
=20
system information for an image in the same way that ArcView 3.x does. For=
=20
example, what if the image is a GeoTIFF file (with coordinate system=20
information embedded in the TIFF file) but you also have a world file (TFW)=
=20
with different coordinate system information? ArcView 3.x will read the TF=
W=20
first, but ArcView 8.x will read the GeoTIFF embedded information first.
For more information on this, see these two ESRI Knowledge Base articles:
http://support.esri.com/search/KbDocument.asp?dbid=3D14147=20
http://support.esri.com/search/KbDocument.asp?dbid=3D18640
Another possible source of your problem could be that the shapefile project=
ion=20
is incorrectly defined. The shapefile projection information created & use=
d by=20
ArcGIS 8 is stored in a *.prj file. You can view and edit the projection=
=20
information for a shapefile in ArcCatalog. Open the Shapefile Properties=
=20
dialog box. Under the Fields tab, select the Shape field. In Field=20
Properties, click on the ellipse (...) next to Spatial Reference. You can=
=20
select a predefined coordinate system here.
For more information on this, do a Search for "Defining a shapefile's=20
coordinate system" in the ArcGIS 8 Help.
Hope that helps!
sarah
email. northms@telus.net
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