Data
Appendix 1: Ground Control Points for Puerto Rico and the U.S. Virgin Islands
Ground control points (GCPs) were used to georeference and mosaic the aerial photos and also to measure the positional accuracy of completed mosaics. GCPs were collected in 1999 and 2000. A preliminary examination of the original TIF images was conducted prior to collecting GCP data to identify sites likely to provide easily identifiable features that could be located in the field and used to mark the position of individual pixels in the imagery. An average of 1 GCP was collected per aerial image. All GCPs were recorded using DGPS and are believed to be accurate within ± 1 meter, which is smaller than the dimensions of pixels generated from scans of the 1:48000 scale photography. At each GCP site, elevation was estimated when possible and included in the data table.
GCP data is split into geographic regions as noted below. To access data for each region click directly on the map within the area of interest. For each region, the general location of each GCP is displayed at a broad scale on shoreline maps of the area, at an intermediate scale on resampled images (JPGs) of the entire photographic frame in which the point was taken, and at a very fine scale in which the specific pixel displaying the exact location of each GCP is noted in red (black dots for the USVI). The UTM coordinates for each GCP can be downloaded as a tab-delimited text file by clicking the link at the bottom of the data table for each region. Additional information regarding specific GCPs may be available for some areas through the contact listed below.
To view GCPs for a specific area of Puerto Rico and the U.S. Virgin Islands, click on a region of the map outlined in blue.
For additional information contact
Matt Kendall via e-mail: matt.kendall@noaa.gov