NOTES ON GEOREFERENCING OF DIGITAL T-SHEETS
A few comments below on the images and georeferencing process. For a detailed description of image georeferencing, refer to the appropriate manual for your software, as the mechanics differ between packages .
Paper historical T-sheet maps contain lines of latitude and longitude among other survey data. These lines were used to georeference the sheets using ERDAS IMAGINE TM 8.4 software.
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
The sheets were scanned at a resolution of 400 x 400 dpi. The files were saved in tagged image file format (*.tif). Scanning was completed in 2001 by C. Van Arsdall at the USGS National Center in Reston, VA. Georeferencing and CDROM were completed in 2001 by P. Briere at the FL Caribbean Science Center in Gainesville, FL.
Files not georeferenced have the following naming convention, T-4371.tif. Georeferenced files (GEOTIFFs) are in a compressed form and when uncompressed have the following naming convention, 4371_geo.tif.
Control points were converted to UTM coordinates before resampling the images. A minimum of 4 control points were used to reference each image, with a RMS error < .05 pixels accepted.
The GEOTIFFs conform to UTM Zone 17 coordinate system, Clarke 1866 spheroid, NAD 27 datum, with meters as the units. The paper maps were based upon NAD 27 and this datum was retained in the GEOTIFFs.
Most of the paper maps were drawn to a scale of 1:20,000. Three of the maps (5862, 5863, 5866) at the northern extent of the study area were drawn at 1:10,000. These maps were not included in the mosaic. They are included as individual GEOTIFFs.
The t-sheets between 4371, 5866, and 5863 are not included on this CD. They currently do not reside in the T-sheet set at the U.S. Geological Survey, Biological Resources Division, Florida Caribbean Science Center.
The mosaic GEOTIFF covers a large regional extent, and when viewed at a reduced scale may not appear to have any data associated with it. For optimal viewing of the data view at full resolution. The mosaic was resampled with an output cell size of 5m x 5m to produce a file of usable bulk.
Specific information regarding aerial photography dates varies by map and is located on each map in both paper and digital form, except the digital mosaic. This information was cropped to produce a mosaic with minimal collar (white space) and maximum vegetation data.
-- PRB 2002
