3D VIEWS OF TREES AND FOREST SAMPLE PLOTS Christopher Legg The spatial distribution of trees in forest sample plots can be analysed statistically and using a two dimensional GIS, but it is often useful to be able to visualise relationships between trees in three dimensions. Methods have been developed for generation of 3D trees, as well as views of the area around forest sample plots, as an aid to spatial analysis

ELEVATION DATA contour maps field altimetry field GPS indirectly from slope measurements Spot-heights of 10*10m sub-plots adjusted based on measured slopes and nearest contour lines

PRODUCTION OF DIGITAL ELEVATION MODEL Convert contours and spot-heights to TIN (triangulated irregular network) using streams and rivers (if available) as breaklines Convert TIN to GRID (raster digital elevation model) with a cell size appropriate to sample plot size

ADD FRACTAL NOISE FOR A MORE REALISTIC SURFACE 3D view of a raw digital elevation model derived from a TIN. The surface looks too “smooth” and retains many artefacts from the TIN The same surface after addition of fractal “noise” using Leveller software. The appearance is more realistic and some of the TIN features have been masked

ADD SAMPLE PLOTS AND CONVERT TO VRML Areas and numbers of forest sample plots are exported as a bitmap and merged with the “noisy” DEM before conversion to a Virtual Reality Modelling Language (VRML) file for easy viewing and manipulation with a free VRML browser such as CosmoPlayer. 3DEM70 software is used.

CROWN DIAMETERS OF TREES crown diameters are not usually measured during forest inventory data is available for some forest plots studied in greater detail regression of crown diameter against trunk diameter shows a good correlation within individual tree families regression coefficients can be used to estimate crown diameters by tree family within sample plots where crown diameter is not measured in the field Production of realistic 3D models of trees requires knowledge of crown diameter as well as trunk diameter, tree height and height to first branch Trunk diameter and crown diameter of Dipterocarps, Batang Ule plot, Jambi

PREPARING DATA FOR 3D TREE GENERATION Three data sets are required to produce 3D trees tree locations with individual tree dimensions polygons of the area of each sample plot an elevation surface of the area around the plots Locations of trees within a single 100*10 metre sample plot Tree locations superimposed on an elevation surface

MAKING 3D TREES Three dimensional trees are generated as graphic objects in ESRIs ArcView 3D Analyst software, using an Avenue script written for this purpose. The script obtains the tree location, tree height, height to first branch, tree diameter and estimated crown diameter from the tree attribute table, and the elevation of the base of the tree from the elevation surface. Tree trunks are simplified as octagonal cylinders, and canopies as octagonal inverted cones covered by a hemisphere. Canopy and trunk colour depend on the tree family. Graphic objects are exported to VRML for easy viewing.

FURTHER PROCESSING 1. Clean VRML files 2. Link VRML files to ArcView VRML files generated by ArcView 3D Analyst are very large, and contain much redundant information. This reduces display speed and occupies disk space. Software called CHISEL removes spurious information and condenses VRML files to about half their original size. VRML views of forest sample plots are linked to the polygons enclosing these plots by HOT-LINKING. The attribute table for each polygon must contain the file name and location of the VRML view, and a hot-link script must call the Netscape (or Internet Explorer) VRML browser.

The VRML plot with trees can be manipulated in real time with a free web browser Clicking within a plot in ArcView opens the VRML file for that plot Information on each tree in the plot can be obtained through the ArcView information tool THE FINAL PRODUCT AND USER INTERFACE