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Information about 3D Analyst - Lake Lorelindu by GRASS

Published on May 24, 2007

Author: httsan

Source: slideshare.net

Calculating the volume of Lore Lindu Lake using GRASS

by Wen Wen

by Wen Wen

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Introduction Geographically, Lore Lindu Lake was located at 1 20’ S and 120 05’E or 50 km south east from Palu, Donggala / Poso District, Central Sulawesi. The total area of the Lore Lindu Lake is 4,250 ha. It is one of the wetland area in the Lore Lindu National Park. Figure 1.1 Lore Lindu Lake

Objectives The objective of this presentation are as the following; To exhibit how to calculate the volume of the Lore Lindu Lake To discover the ground area of the surface

The objective of this presentation are as the following;

To exhibit how to calculate the volume of the

Lore Lindu Lake

To discover the ground area of the surface

Data a. Lore Lindu Lake area (polygon vector data) b. Depth (a dBase file containing x, y, and z information ( easting, northing, depth water)

Vector Data of Lore Lindu Lake Import point x, y, z lindu lake depth (v.in.ogr) Surface Interpolation IDW r.surface.idw Lore Lindu Lake Bathymetry map Lore Lindu Lake Slope map Lore Lindu Lake contour map 3D Viewing (NVIZ) Calculation of the volume (r.volume, r.lake)

General Processing in GRASS GIS A. Create database, location and mapset B. Type Grass62, gis.m command and GRASS environment

C. Import of GIS data using v.in.ogr shapefile select the lake.shp file and depth.shp that have merged into one file lake depth.shp (v.in.ogr in=lakedepth.shp out=lakegrass)

D. Surface Interpolation The method is based on an assumption that the value at an unsampled point can be approximated as a weighted average of values at points within a certain cut-off distance, or from a given number m of the closest points (typically 10 to 30). Where p is a parameter, GRASS modules use p = 2. Inverse Distance Weighted Interpolation

Lake bathymetry was created with r.sufr.idw for Lore Lindu Lake

Contour and Slope Map for Lore Lindu Lake

E. 3 D Analysis View in GRASS using NVIZ

F. Volume Calculation To compute volume of Lore Lindu Lake, the r.volume command in GRASS will be used. Define the minimum by running r.univar command after masking all areas except the Lake boundary: r.univar lake.depth [….] Minimum : -13.4 Maximum : 0 r. mapcalc volume=“lake.depth” r.volume volume Result output for calculation of the Lore Lindu Lake Volume is = 143449194.374 m3, Surface Area = 34801844.615 m2 For other analysis, new command such as r.lake can also be used.

Conclusion Volume calculation of Lore Lindu Lake can be applied for water volume calculation with different time scale then increasing or decreasing of the water volume can be analyzed as the hydrology analysis. GRASS Open Source GIS can provide easy access and flexibility in input data, interpolation, 3 D viewing, and for volume calculation as 3 D analyst in Lore Lindu Lake as well as the commercial GIS software packages.

Thank You

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