Digital Photogrammetry – State of the Art and Potential for Application in Forest Management in Croatia

Abstract

Background and purpose: The main goal of this paper is to inform forestry community about the latest developments in digital photogrammetry, as well as to present its possible application in forest management. For this purpose, the current state of technological development of the main tools of digital photogrammetry (digital aerophotogrammetric cameras and digital photogrammetric workstations) has been presented. Furthermore, two adjusted methods of manual digital photogrammetry for application in forest management, namely: method for strata delineation (i.e. creation of forest management division), and method for measuring stand structure elements have been developed and presented here. Material and methods: Research was carried out on the selected part of multi-aged, privately owned forest of ''Donja Kupcina - Pisarovina'' management unit which includes 6 compartments and 24 subcompartments and covers total area of 480 ha. After conducted aerial survey of research area, acquired digital images were processed, and digital terrain model and digital elevation model were derived. Digital aerial images of ground sample distance of 10 cm, topographical maps, digital terrain model and digital elevation model, as well as the digital photogrammetric workstations with appropriate software (PHOTOMOD, Global Mapper) were used for developing methods for strata delineation and stand structure elements estimation. Developments of both methods were carried out in the stereomodel of colour infrared digital aerial images in PHOTOMOD StereoDraw module. Additional data processing was conducted in ArcGIS 9.1. (for strata delineation) and in Global Mapper (for stand structure elements estimation) software. Discussion and conclusions: This research has showed that PHOTOMOD Lite and Global Mapper software packages in combination with the used materials (digital aerial images, digital elevation model) and digital photogrammetric workstation completely satisfy the needs for strata delineation and stand structure measurements. The PHOTOMOD software enables simple creation of projects of digital images, easy manipulation of multiple digital images, and many other features that facilitate photogrammetric measurement and photo-interpretation, but its free version PHOTOMOD Lite has limited capabilities in terms of number of images and quantity of vector data that can be processed. If digital images of high spatial resolution are used (e.g. 30 cm or better), as was the case in this research, stereo- effect experienced by the operator and the quality of photo-interpretation are very good. That enables clear determination of vegetation types and as well as single tree species, more accurate pinpointing of tree tops and more accurate delineation of tree crowns. As long as automatic procedures are not available, digital photogrammetry has to rely on manual methods. Allometric relation between variables measured with photogrammetric method and desired variables need to be developed. An attempt to address this issue, at least in part, is made within the ongoing project 'Application of digital photogrammetry in practical forest management'.