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GIS.NY.GOV

NYS ITS GIS Program Office

Geographic Information Systems Clearinghouse

Glossary: Terminology for Digital Orthoimagery Program (DOP)

Aerial Photography
Aerial photography is any photography taken from the air. Typically, aerial photographs are taken with specialized, high-quality, large format cameras that point down vertically from the aircraft to the ground below. Orthophotography is derived from overlapping vertical aerial photography.
Color Infrared (CIR)
A "false color" film type which senses information in the green, red, and near-infrared portions of the spectrum. On CIR imagery, near-infrared will appear as red; red will show as green; and green as blue. Blue is not detected. Commonly used for vegetative mapping, natural resource assessment, and environmental analysis. CIR depicts health of vegetation, soil moisture, and other environmental factors.
Digital Orthoimagery (DOI)
Digital Orthoimagery - a remotely-sensed digital picture, stored in a raster data format. It is a georeferenced image prepared from a vertical photograph or other remotely-sensed data in which displacement of objects due to sensor orientation and terrain relief have been removed.
Digital Terrain Model(DTM)
Digital Terrain Model is a sample of terrain elevations points used to model a land surface. It is a required element in the processing of digital orthoimagery based on the accurate identification of control points in the images whose ground positions are accurately known.
Geographic Registration
The spatial referencing of an orthoimage to an area on the earth's surface. An image must be geographically registered in order to use it in a GIS as an overlay.
Ground Control Point
Points of accurately known geographic location used to register imagery and other coverage data to ground position.
Ground Sample Distance(GSD)
The area on the ground represented by each pixel in a digital orthoimage.
High Accuracy Reference Network (HARN)
The HARN is a statewide network of survey monuments measured to an extremely high level of accuracy with respect to, and as part of, a similar nationwide network of high-accuracy points. The positions of these monuments are established using Global Positioning System (GPS) and other sophisticated space-based measuring technologies. The purpose of basing the geographic positioning of the Statewide Digital Orthoimagery Program on the HARN is to ensure uniform and accurate ties of the orthoimagery to the physical world, and to ensure compatability with other data sets tied to the national network.
Image Catalog
There is an image catalog, 00IC*.dbf file, associated with all of the .jp2 or .sid files for each geographic area. The image catalog uses a system environment variable, $NYSDOP. In order to use an image catalog, the user must set the system environment variable on their machine before using the ESRI software.
Metadata
Metadata provides information about the content and origins of a particular set of data.
Multi-spectral
Digital orthoimagery collected in multiple bands, with each band corresponding to a portion of the spectrum. Various band combinations may be combined to assist in the identification of specific ground features, via automated image processing techniques.
Natural Color
A film type which senses the same portion of the spectrum as human vision. Commonly used for inventory analysis, cartographic verification, and data verification. Especially useful for showing man-made features, which typically occur in a wider range of colors than natural features.
Panchromatic
A film type which renders imagery as gray scale. It generally provides the best contrast and least amount of storage space.
Positional Accuracy
This refers to the variation that can exist between coordinates for a feature on the image to the actual location of that feature on the earth's surface.
Remote Sensing
The process of collecting data about objects or landscape features without coming into direct physical contact with them
Scale
Ratio of distances on a map to those same distances on the earth's surface.
Seamless Table
A seamless table is comprised of 4 MapInfo files. There is a seamless table associated with all the .jp2 or .sid files for each geographic area. The seamless table files MUST be in the same directory as their associated files. Open a seamless table as you would open any table in MapInfo. For more information, consult the Help section in MapInfo software.
State Plane
A coordinate system (grid) of plane rectangular (x, y) coordinates for pre-determined zones in each of the 50 states. Units are in feet. It is primarily used by local governments. New York contains 4 zones: West, Central, East and Long Island.
Tiling
Images are subdivided into smaller units to reduce the physical file size and the amount of computer processing required. Tiles usually cover a regular rectangular grid.
Universal Transverse Mercator (UTM)
A map projection and coordinate system, pre-defined for 60 zones spanning the globe. Units are in meters. New York is primarily in zone 18.