2016 Orthoimagery JPEG2000 AUX File Problem

Summary
The VT Center for Geographic Information (VCGI) has identified a problem with the compressed versions of Vermont’s 2016 orthoimagery.  This posting describes the problem as well as procedures for fixing the problem depending on how the user acquired the imagery.
Description of Problem
The 2016 orthoimagery was delivered in two raster formats; 1) TIFF and 2) JPEG2000 (*.jp2).  These files were accompanied by associated “auxiliary files”, which are files with an *.aux and *.aux.xml extension.  These files are often generated by Esri software and contain “configuration” information which can affect how Esri and other software interact with raster files.
 
VCGI has determined that the aux files accompanying the JPEG2000 files included invalid configuration information which causes raster cell values equal to zero (0) to be interpreted as “nodata” by Esri software (as well as some other GIS packages such as QGIS).  Visually this manifests itself as “speckle” in the imagery, however, it can also make its way into derivative raster data since geoprocessing routines will interpret zeros as nodata.
Solution
The problem can be easily resolved by removing the *.aux and *.aux.xml files accompanying the JPEG2000 files.  VCGI has already removed these files from the systems we manage (e.g. VT Open Geodata Portal).  Please refer to the procedures outlined below to remove any offending 2016 orthoimagery “aux” files from your system.
  • VT Open Geodata Portal (Portal):  Use this procedure if you downloaded the imagery via the Portal.  NOTE: By default, the Portal’s “Tiled Data Download Tool” will only give users the *.jp2 file, meaning you won’t have any *.aux or *.aux.xml files to worry about.  However, if you bypassed this interactive selection tool and “bulk downloaded” directly from the web folder then you’ll need to follow these procedures (assumes Windows OS).
  1. Browse to the folder where you downloaded the files.
  2. Sort on the “type” column.
  3. Carefully Select and Delete all *.aux and *.jp2.aux.xml
  4. Repeat for all 2016 orthoimagery datasets (e.g. 30cm, 15cm, black & white, color).
  • Offline Data Product:  If you ordered an offline product containing the 2016 imagery
  1. Browse to .\VIL\IMAGERY\VTORTHO\0_3M\CLRIR\2016\COMP
  2. Sort on the “type” column.
  3. Carefully Select and Delete all *.aux and *.jp2.aux.xml
  4. Repeat for these folders
    .\VIL\IMAGERY\VTORTHO\0_3M\PAN\2016\COMP
    .\VIL\IMAGERY\VTORTHO\0_15M\CLRIR\2016\COMP
    .\VIL\IMAGERY\VTORTHO\0_15M\PAN\2016\COMP
Question? Contact Steve Sharp, VT Ortho Program Manager at steve.sharp@vermont.gov.