The Coastal Ecosystem Mapping and Media Viability Project

Figure 22. Volume output calculations from Pix4D of the selected tree feature. Volume values are given in the Properties table on the right hand side. This particular mangrove tree has a total volume of 65.53m3 as computed by Pix4D. Photo 2. Volume output calculations from Pix4D of the selected tree feature. Volume values are given in the Properties table on the right hand side. This particular mangrove tree has a total volume of 65.53m 3 as computed by Pix4D. The advantage of calculating volume in Pix4D is that it is simple and works well for unique trees surrounded by bare ground. However, there needs to be bare terrain around a tree or group of trees for Pix4D to evaluate the terrain elevation that it uses as a base to calculate volume. In the case of large tree canopies, Pix4D is not able to correctly evaluate volume because it has no information on the elevation of the base terrain under the feature for which it calculates volume. In the next section, we explain how volume calculations can be obtained using GIS software and the orthomosaic and Digital Surface Model (DSM) outputs from Pix4D to circumvent the limitations mentioned above. Calculating Volume using GIS Software We chose to use ArcGIS 7 to process our orthomosaic and DSM raster datasets to calculate mangrove tree volume. To calculate mangrove tree volume we use the following formula: tree average height x tree base area . The three main steps are as follow: distinguishing tree from non-tree features in our study area, estimating the average tree height and base area values, and finally determining the tree volume.

7 We are also evaluating the options of using open source GIS software, particularly QGIS, to process the same data and obtain mangrove tree volume estimates.

The Coastal Ecosystem Mapping and Media Viability Project

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