3D VIEWS OF TREESAND

FOREST SAMPLE PLOTS

Christopher Legg

The spatial distribution of trees inforest sample plots can be analysedstatistically and using a two dimensionalGIS, but it is often useful to be able tovisualise relationships between treesin three dimensions.Methods have been developed forgeneration of 3D trees, as well as viewsof 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*10msub-plots adjusted basedon measured slopes andnearest contour lines

PRODUCTION OF DIGITAL ELEVATION MODEL

Convert contours and spot-heightsto 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 elevationmodel derived from a TIN. Thesurface looks too “smooth” andretains many artefacts from the

TIN

The same surface after addition offractal “noise” using Leveller

software. The appearance is morerealistic 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 witha 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 ofcrown 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 GENERATIONThree 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 oftrees withina single 100*10 metresample plot

Tree locations superimposed on an elevation surface

MAKING 3D TREESThree dimensional trees are generated as graphic objects in ESRIsArcView 3D Analyst software, using an Avenue script written for thispurpose. The script obtains the tree location, tree height, height tofirst branch, tree diameter and estimated crown diameter from the tree attribute table, and the elevation of the base of the tree from theelevation surface.

Tree trunks aresimplified as octagonalcylinders, and canopiesas octagonal invertedcones covered by ahemisphere.

Canopy and trunk colour depend on thetree family.

Graphic objects areexported to VRML foreasy 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 displayspeed and occupies disk space. Software called CHISEL removesspurious information and condenses VRML files to about halftheir original size.

VRML views of forest sample plots are linked to the polygonsenclosing these plots by HOT-LINKING. The attribute table foreach polygon must contain the file name and location of the VRMLview, 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 plotin ArcView opens theVRML file for that plot

Information oneach tree in the

plot can be obtained through

the ArcViewinformation tool

THE FINAL PRODUCT AND USER INTERFACE