XYZ2DEM Importer - Import a DEM image of Nantucket Island
Import a Digital Elevation Model image of Nantucket Island. This example demonstrates the typical use of XYZ2DEM Importer using a real world data set. Using a proper chosen Maximum edge length parameter, we additionally obtain an approximate coastline.
Screenshot: Preliminaries: Proceeding:
- Import nantucket.txt:
Plugins > XYZ2DEM Importer: nantucket.txt
using the following set of input parameters:
Length of one pixel: 7.5
Maximum edge length: 100.0
Background value: -1.0
- Save DEM image:
File > Save As > Tiff...
- Apply Look Up Table:
File > Import > LUT... : nantucket_lut.txt
Discussion: The points in the data set can be divided into more or less regularly spaced mass points at the one hand and points on breaklines, which show shorter distances to each other in general, at the other hand. This particular character of the point distribution preserves the breaklines, although no edge or line constraints are applied during meshing and interpolation. (Cf. the according concept of a Conformed Delaunay Triangulation).
The blue background value in the resulting DEM image indicates areas without height information, both ocean and lakes. The outlines of these areas simply result from omitting every surface triangle which exceeds the user chosen Maximum edge length of 100.0m. This is a very quick and easy way to determine approximate outlines - often satisfactory, if the point density is more or less regular. Nevertheless, the accuracy of the resulting outline is limited by the point density of sparse areas.
Since this data set offers varying point densities, a boundary polygon with higher precision can be obtained from the original data with the help of a Geographic Information System (GIS). For comparison, we prepared another example: How to import the DEM image of Nantucket using a ROI polygon.
Credits: The data set nantucket.txt is a compilation of Digital Terrain Model data kindly provided by the Office of Geographic and Environmental Information (MassGIS), Commonwealth of Massachusetts Executive Office of Environmental Affairs.