Digital True Ortophoto

True orthophoto term is defined in the orthophoto are objects that are defined by digital terrain model translated in orthogonal projection. Orthophoto accuracy lies in the quality and accurately collected data digital terrain model (in this claim implies correctly completed recording and aerotriangulation). On the positional accuracy of these objects affect the laws of geometry of the central projections and they are depending on their horizontal distance from the center of the recording and the vertical distance from the digital terrain model replicated on orthophoto with higher or lower position error, which comes to the fore during the overlap with other spatial data. Objects are deformed, such as buildings seem laid in relation to the center of the recording (the visible side walls) and the bridges and viaducts to lose the original shape. These moving objects are hiding information, so high the building can cover a small building of streets and infrastructure, which significantly reduces the value of the orthophoto as a source of spatial information. In order to avoid or reduce to the minimum using the process of true orthophoto.

Therefore it is necessary to collect information about buildings and create a digital model of objects (DBM - digital building model). Data is collected mapping boundary line of tops of buildings. Private buildings and houses, which make the most of digital models of buildings, collecting the roof edge lines. Depending on the level of detail and accuracy of the required project, can collect all the details on the roofs (ridge of the roof, skylights, chimneys,...). The collected data is then projected vertically onto a digital terrain model and created a digital model of objects (DBM). Together, they form a digital surface model (DSM) which is the only correct model and it can translate all objects from the central projection in orthogonal, in fact make true orthophoto.