Continuous revision of digital cartographic databases : a comparison of methodologies

Abstract

The thesis regards the continuous revision of digital cartographic databases and an analysis, as well as a comparison of the methodologies. This is due to the fact that the increasing development of infrastructure, is a continuous request for the map users. Thus, a cost-effective method with minimal time consumption has to be implied, maintaining the high quality topographic maps available. Three methods of various types of photography for revision of the digital data are considered. These are namely: Aerial photography, Low Altitude aerial photography and Satellite photography. A full description is given as well as the image acquisition, image orientation and data capturing to produce the final product, using different methods. Image acquisition includes the 23cm by 23cm aerial photographs from a specific aircraft using a metric camera, the aerial photographs captured from a low altitude flying plane/helicopter/helium balloon using a semi-metric camera and the one metre resolution digital images from satellites. The various types of image orientation related to the particular type of acquisition are discussed. These include the use of the traditional stereo-plotter or the scanning for orthophotos in the case of large format aerial photos; an analytic plotter or the creation of photo-mosaics after scanning the low-altitude aerial photographs; and regarding satellite imagery, the correction done by the digital terrain model. Data capturing is also analysed, either by digitising points or by on-screen digitising. Apart from revision from various types of photography, analysis of revision from ground surveys or proposed/available plans is even discussed. This is related to digitising of plans available, as well as ground surveying. A detailed explanation is done, of the method of digitising and the types of data formats. Furthermore, ground surveying using basic equipment, that is measuring tapes, together with the use of surveying equipment including total stations and global positioning systems is also examined. The importance of the end user's knowledge of these revisions is also taken into account, as well as some applicable procedures to operate and administrate the databases in a more convenient way. The introduction of software including animations in order to superimpose map files of previous mapping is also mentioned. This shows the dramatically increase in speed and accuracy in the updating process, as well as eliminating the problem of discarding previous data before the revision is done. After examining the various methodologies, a comparison is made, in order to try to establish the best method to be adapted to the current database within this particular organisation. Considering the scenario, it is concluded that, in this case, it would be better off opting for field surveying due to the frequent but minor developments. However, decreasing the current span of full aerial photograph runs, is also considered. In fact, in order to be cost effective, low altitude photography is a suitable option that could be applied.