'Photo maps' add reality to your project and GIS database.
Orthophotography is the combination of high resolution aerial images with an accurate digital terrain model (DTM) to create a map that looks like a photography. The steps to this process are:
- Scanning of Diapositives
- Data Capture and DTM creation
- Rectification of Scanned Photographs
- Seamless Mosaicing of Ortho Images
- Output of Compressed 'Photo Map'
At Bradstreet Consultants, our team uses precision scanning devices with scan resolutions between 12 and 25 micrometers, first order analytical stereoplotters and Autometric's Softplotter NT softcopy photogrammetry software to complete your project to exacting National Map Accuracy Standards.
Scanning of Aerial Photograph Diapositives
Your digital orthophotograph will be created by scanning diapositive transparencies produced from aerial photography using a precision image scanner. The source material to be scanned is a clean set of negatives or diapositives manufactured from the aerial photography (scanning is done prior to using them for FAAT and planimetric/topographic mapping). The precision scanning devices our team utilizes produce scanned photographs with resolutions between 12 and 25 micrometers.
Data Capture and DTM creation
The elevation data used in the rectification process is captured by photogrammetric techniques using first order analytical stereoplotters. This elevation data consists of points spaced at regular intervals along a grid, supplemented by breaklines at all significant terrain breaks which enables our team to create an accurate digital terrain model (DTM) of your project area. One DTM file is provided with each digital orthophotograph, in accordance with the tile system designated.
Rectification of Scanned Photographs
The scanned photographs are differentially corrected to an orthophotographic projection on a pixel-by-pixel basis to create individual ortho images. The horizontal resolution of the resulting ortho image will be 1.0 foot on the ground. If the scanned images result in a resolution of finer than 1.0 foot; resampling methods are used to process the data to the 1.0-foot resolution level.
Seamless Mosaicing of Ortho Images
The edges or match lines of each digital ortho image are carefully inspected for variation in native tone quality and adjusted so that no difference in image quality or appearance is visible with the unaided eye. The individual digital ortho images are combined into a "seamless mosaic" using Autometric's Softplotter NT photogrammetric system. That seamless mosaic is the orthophotography for your project area. All digital orthophotos will be free and clear of blemishes, blurs, and other artifacts.
Output of Compressed 'Photo Map'
From the orthophotograph of the project area, sheets are generated according to the tiling system designated by you. This system of sheets enables Bradstreet Consultants to compress the seamless mosaic into one archive using LizardTech's MrSID image compression software. The Multiresolution Seamless Image Database (MrSID) technology allows seamless wavelet-based compression of images of very large dimension and the local decompression of image subregions at varying resolutions.
The final digital orthophotographs are seamlessly mosaiced, quality controlled, pre-referenced and ready for use in your GIS system. In addition, our digital orthophotography will meet or exceed National Map Accuracy Standards for 1"=40' scale mapping and can be rectified to Plane Coordinate Systems - NAD83 horizontal datum and NAVD88 (feet) vertical datum.
