State Plane Coordinate Georeference Error

[JoeDaleHardin]

I uploaded a large .sid file into GeoViewer. The coordinate system is Alabama West NAD 83 (as shown in status bar) and in metadata. The metadata showed the units to be meters. Upon first view, the scale was badly wrong. I checked a known location and a known distance measurement and the measurements were also wrong. For example, a location known to be 30.29026, -87.67799 was shown to be 30.238183, -79.927923. The distance measurements were 4.23 miles on Geoviewer and 1.32 miles known. This ratio (3.204) is not quite the conversion between meters and feet (3.28), however, this may be a clue. Exporting view to geotiff yields the same error in georeference. The same file inputs into ESRI ok with the proper coordinates, so I suspect something amiss with GeoViewer. Could you check on this? Thanks Dale

[rparker]

I suspect that ESRI is reading more accurate information about the file from auxilliary files. In sounds like the metadata written in the file may be incorrect.

You can use GeoExpress or GeoExpress Tools to update the file with accurate metadata.

Otherwise, you could create a world file (in a text editor) with accurate coordinates.

[JoeDaleHardin]

Here is the solution provided by the aerial photography company:

<snip>Yes, the issue goes beyond the .aux.xml file, which is generated from ArcMap when the .sid is opened. All the info from the .sid geo-header is what populates the .aux.xml file - which is what ArcMap reads for setting the map projection.

If you change the projection in ArcCatalog, it changes just the .aux.xml and ArcMap reads the revised projection from that.

We actually had to use a different process in GeoExpress to populate the .sid geo-header info in units of feet - that is, to create a custom projection. The options for georeferencing Alabama West in GeoExpress do not provide an option for either "meters" or "feet" units. It just has a single option, and apparently, it's meters. If you check other state plane zones, there are separate options for feet and meters when creating the MrSID files. For Arc users, it just worked fine how we were doing it so no issue ever came up. <snip>

Seems a new georeferencing option for Alabama West is needed.

Thanks for your help