Spatial Data - MATLAB Recipes for Earth Sciences - page 251

shading interp
axis equal, view(0,90)
colorbar

h is script opens a new i gure window and generates a colored surface. h e
surface is highlighted by a set of color shades, and is displayed in an overhead
view (Fig. 7.2). Additional display methods will be described in the section
on SRTM elevation data (Section 7.5).

Interactive
7.1

7.4 The 30-Arc Seconds Elevation Model GTOPO30

h e 30 arc second (about 1 km) global digital elevation data set GTOPO30
contains only elevation data, not bathymetry. h e data set has been developed
by the Earth Resources Observation System Data Center and is available
from the U.S. Geological Survey web page

https://lta.cr.usgs.gov/GTOPO30

h e model uses a variety of international data sources but is mainly based
on raster data from the Digital Terrain Elevation Model (DTEM) and vector
data from the Digital Chart of the World (DCW). h e GTOPO30 data set has
been divided into 33 tiles. h e tile names refer to the longitude and latitude
of the upper-let (northwest) corner of the tile. h e tile name e020n40
refers to the coordinates of the upper-let corner of the tile, i.e., longitude
20 degrees east and latitude 40 degrees north. As an example we select and
download the tile e020n40 , which is provided as a 24.9 MB compressed tar
i le. At er decompressing the i le we obtain eight i les containing the raw data
and header i les in various formats. h e tar i le also provides a GIF image of
a shaded relief display of the data.
Importing the GTOPO30 data into the workspace is simple. h e Mapping
Toolbox provides an import routine gtopo30 that reads the data and stores it
onto a regular data grid. We import only a subset of the original matrix:

clear

latlim = [-5 5]; lonlim = [30 40];
GTOPO30 = gtopo30('E020N40',1,latlim,lonlim);

h is script reads the data from the tile e020n40 (without i le extension) at full
resolution (scale factor =1) into the matrix GTOPO30 , which has the dimensions
of 1,200 by 1,200 cells. h e coordinate system is dei ned by using the lon/lat
limits listed above. h e resolution is 30 arc seconds, corresponding to 1/120
of a degree.

[LON,LAT] = meshgrid(30:1/120:40-1/120,-5:1/120:5-1/120);