A geographic information system (GIS) is a computer system for managing the geometric and attribute data of a certain geographical object. A digital aerial photograph is exposured either with a conventional film camera and scanned with a scanner or taken directly by a digital detector. Recent developments in digital photogrammetry have brought fair priced desktop solutions to municipal surveying departments. Digital photographs have become an essential part of the GIS.
Organizations, which have not extensively used aerial images in digital form, have to be aware of the basic principles of photogrammetry, such as resolution, opening angle and overlaps, mission planning of flight, aerial triangulation, collinearity equations and the effect of a digital terrain map to the quality of orthophoto. The determination of projection centers with global positioning system (GPS) reduces the amount of signalized points and enhances the accuracy. Gyrostabilized camera mounts greatly improve the resolution by reducing image blur due to turbulence. Persons dealing with orders are supposed to know the legislative status of digital aerial photographs and the concept of security inspection.
The image can be classified as a nadir picture taken with a metric camera or an amateur camera, an oblique picture taken with a metric or an amateur camera or an orthophoto created from a metric nadir picture. For presenting georeferenced data the images can be used as such or with raster/vector overlaying. Measurements can be done both monoscopically and stereoscopically. The value of the digital era lies in the automatization of previously time-consuming stages, such as the interior orientation, the measurement of tie points and the creation of a digital terrain model from lightly vegetated areas. The inclusion of these properties is of course software dependent.
Stereoscopic measurements are used in the maintenance of the base map for town plan, the following of the residual soil dumping and the creation of terrain models. Orthophotos can be utilized as a background material in GIS and as a core of a new kind of base map for town plan. Land use, street, park, green belt and water drainage planning, house construction control, environmental control, emergency services, statistics and research and many others can use orthomosaic clipped to match the sheet index. Oblique photographs form a versatile information source, for which the presentation use is emphasized.
Digital images can be spread around through intranet or internet to a large number of different users. The biggest user group is viewers, then comes utilizers and analyzers. The smallest group is maintainers.
Keywords: Digital aerial image, geographic information system, orthophoto, oblique photo, base map for town plan, land use planning, digital terrain model, gyrostabilization, planning, residual soil , accuracy, scanner, master plan