Mylar photo-basemaps were scanned at 300 dpi on an Oce TC4 Wide Format Color Scanner. Images were captured in uncompresssed tif format using a default contrast setting. A complete digital archive was created, consisting of approximately 1621 basemap images. Each image was named using the following convention: 1977_xxx_xxxxa.tif, where xxx_xxxx = the basemap number, and a = designation for archived image. Basemap numbers were assigned according to the New Jersey State Plane Coordinate System NAD27, in Feet, included at the lower left extent of the image. The first three digits of the map number are the first three digits of the northing (y-coordinate) value. The following four digits of the map number are the first four digits the easting (x-coordinate) value. Note that while the basemap and image numbers retain the NAD27 values, these scanned images are referenced in New Jersey State Plane Feet, NAD83.
Scanned images were georeferenced using four (4) reference points at the corners of grid embedded into the images matched to the corresponding corners of the NJDEP Tidegrid vector digital data. The resolution and contrast in the images, particularly over water bodies, occasionally made it difficult to select exact corner points. Every effort was made to select the source georeference points at pixel boundaries rather than within pixels as a means to minimize residuals.Additional vector data referenced were the NJ DOT road centerlines. These data provided supplemental visual cues to ensure that each basemap was properly placed. There was a single instance of a basemap bearing the incorrect image number, and use of the road vectors enabled proper placement of the image. The source dataset included some overlap between images, approximately 60 - 100 ft beyond the grid boundaries in each basemap. Each image was saved in 8 bit uncompressed tif format, and named using the following convention: 1977_xxx_xxxxsp.tif, where xxx_xxxx = the basemap number, and sp = designation for images georeferenced to the State Plane coordinate system.
A polygon shapefile was created for each image representing the extent of each image to be cropped from the full georeferenced image. Criteria were to include a narrow image overlap, so that cropped images could easily be processed into a seamless raster mosaic.Using the Tidegrid shapefile, a new polygon shapefile was created for each image to be processed. The crop polygon extended thirty (30) feet outside each tidegrid polygon; this distance was selected to preserve an adequate overage while removing marginalia.Each shapefile was named for its corresponding image using the following convention: 1977_xxc_xxxxext.shp, where xxx_xxxx = the basemap number, and ext = designation for crop extent.
Images to be cropped were grouped with their respective polygon shapefile into folders for processing. An automated script was used to perform the cropping function, where output images were placed into a holding area to facilitate quality control and tracking of progress.Each cropped image was stored in 8 bit, uncompressed tif format, and named using the following convention: 1977_xxx_xxxxcrp.tif, where xxx_xxxx = the basemap number, and crp = designation for cropped images.
Quality control reviews were performed on a random sample of images scattered throughout the State. The selected images were rendered along with the tidegrid vectors to determine spatial alignment with the grid. Georeferencing specifications were +- four (4) feet, and the majority of images met or were better than this criteria. For those that were outside the specification, comparison with bordering images showed that in some cases the embedded grid appear to have been poorly placed when comparing grid locations to features on the ground common between the two images. Additional complications of note include changes from use and age to the chrono-flex originals such as creasing, denting, scratching, and stretching. Precautions and care were taken to minimize any possible distortions brought about by the scanning process, though the age and material of the originals may have introduced some distortion.
The entire image library of full scanned images was also converted to 8 bit jpg compressed format to produce the final deliverable. Each image was named using the following convention: 1977_xxx_xxxxa.jpg where xxx_xxxx = the basemap number, and a = designation for archived images.
The delivered JPEG2000 images were reprocessed using Lizardtech GEOEXPRESS 8.5 to create MrSID MG4 format. These images were indexed to create a WMS using Lizardtech Express Server.
Metadata for the 1977 processed imagery was edited to document the WMS built on the images.
Metadata were updated to correct format errors and reflect the re-named and re-published service.
A pixel value number from 0 to 255 will be assigned to each pixel. This number refers to a gray shade value on a stretched color ramp from black to white. Each pixel will be assigned a value from 0 to 255, black to white, depending on the symbology method and stretch type selected.