Raster spatial reference issue in 10

[LisaNelson]

Hello,

I'm looking for insights on why the spatial reference of an IMG raster (it's big, that's why it's in IMG format) displays as 'NAD_1983_Albers' in ArcGIS 10 and 'USA_Contiguous_Albers_Equal_Area_Conic_USGS_version' in ArcGIS 9.3.1.  This inconsistency is present in Python SpatialReference objects (both arcpy and arcgisscripting flavors) and in the ArcMap Layer Properties GUI. 

I can code around it, but it seems like a potential bug.

Thanks,
Lisa

[MelitaKennedy]

Hello,

I'm looking for insights on why the spatial reference of an IMG raster (it's big, that's why it's in IMG format) displays as 'NAD_1983_Albers' in ArcGIS 10 and 'USA_Contiguous_Albers_Equal_Area_Conic_USGS_version' in ArcGIS 9.3.1.  This inconsistency is present in Python SpatialReference objects (both arcpy and arcgisscripting flavors) and in the ArcMap Layer Properties GUI. 

I can code around it, but it seems like a potential bug.

Thanks,
Lisa

Hi Lisa,

Esri stores coordinate system information by well-known ID (wkid aka "code" or EPSG code) and by well-known text (WKT). Sometimes Esri adds a coordinate system with a particular name, then EPSG, an external authority, adds the same definition with a different name. Each also has different wkids. When we can we will update an Esri entry to use the EPSG wkid because that's a more widely accepted authority. Rasters are more complicated than vector data because of the different formats. The coordinate system information is stored differently in the various file formats. In this case, possibly the wkt from 9.3.1 is mapping to the 10 wkid, which has a different wkt in the IMG format code!

Melita

[curtvprice]

We have run into into this with our NHDPlus processing with the Esri GRID format.

If we have a raster or do some processing using the spatial reference labeled USA_Contiguous_Albers_Equal_Area_Conic_USGS_version (Esri WKID 102039, SR-ORG:6703) this is saved in Esri grids as NAD_1983_Albers and this label propagates through using map algebra or Copy Raster to other formats (like .tif) that do support the standard label. I posted an incident request on this, I really think the raster tools should sniff out at least some projections on their way out of Esri grid format, which is still the most efficient format to use for some processing. This issue will be become less common with 10.5 and later, which has an update to map algebra which does not save temp rasters through the grid format (it now creates temp rasters using .tif).

This is recorded by Esri as

[NIM058732: When projecting ESRI GRID to 'USA_Contiguous_Albers_Equal_Area_Conic', the resulting projection becomes 'NAD_1983_Albers'.

https://support.esri.com/en/bugs/nimbus/TklNMDU4NzMy 

though: the problem exists whenever saving any raster to Esri grid format that is in this projection, not just when projecting!

Example:

Input .TIF, reported from Describe as this (although the tif tags don't seem to have a this label anywhere)

USA_Contiguous_Albers_Equal_Area_Conic_USGS_version

Here's the prj.adf file for this raster when saved to Esri grid format:

Projection ALBERS
Datum NAD83
Spheroid GRS80
Units METERS
Zunits 100.0 /* NAVD_1988 - VCS# = 5703
Xshift 0.0
Yshift 0.0
Parameters 
 29 30 0.0 /* 1st standard parallel
 45 30 0.0 /* 2nd standard parallel
 -96 0 0.0 /* central meridian
 23 0 0.0 /* latitude of projection's origin
0.0 /* false easting (meters)
0.0 /* false northing (meters)‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

When this grid copied to .TIF (in the .tif tags):

PCS Name = NAD_1983_Albers
‍‍‍

[LisaNelson]

Thanks for the reply, Melita.  

It appears no EPSG code (WKID) exists for this spatial reference (http://spatialreference.org/ref/sr-org/6703/), although a SR-ORG Id does (6703).

I got around it using the SpatialReference.projectionCode property, which is consistent between 9.3.1 and 10.

Lisa

[curtvprice]

I've gotten into the habit of using the WKID in Python because the names can be quite inconsistent. Then tools like the Define Projection tool can handle the inconsistencies between the different file formats (we hope, and they usually do -- if the raster format supports the projection).

For example, CONUS Albers USGS version using Esri WKID (found by looking in ArcMap data frame properties): arcpy.SpatialReference(102039)