Geoscience Reference
In-Depth Information
Finally, we can display the entire image using
imshow(HYPC)
or, as an alternative, that part of the image showing the Barrier Volcanic
Complex in the northern Suguta Valley (Fig. 8.5).
imshow(HYPC(900:1100,:,:))
Exporting the image is possible in many dif erent ways, for example using
print -r600 -dtiff barrier.tif
to export it as a TIFF i le
barrier.tif
with a resolution of 600 dpi.
8.7 Digitizing from the Screen
On-screen digitizing is a widely-used image processing technique. While
practical digitizer tablets exist in all formats and sizes, most people prefer
digitizing vector data from the screen. Examples of this type of application
include the digitizing of river networks and catchment areas on topographic
maps, of the outlines of lithologic units on geological maps, of landslide
distributions on satellite images, and of mineral grain distributions in
microscope images. h e digitizing procedure consists of the following
steps. h e image is i rst imported into the workspace. A coordinate system
is then dei ned, allowing the objects of interest to be entered by moving a
cursor or cross hair onto it and clicking the mouse button. h e result is a
two-dimensional array of
xy
data, such as longitudes and latitudes of the
corner points of a polygon, or the coordinates of the objects of interest in a
particular area.
h e function
ginput
included in the standard MATLAB toolbox allows
graphical input from the screen, using a mouse. It is generally used to
select points, such as specii c data points, from a i gure created by an
arbitrary graphics function such as
plot
. h e function
ginput
is ot en used
for interactive plotting, i.e., the digitized points appear on the screen at er
they have been selected. h e disadvantage of the function is that it does not
provide coordinate referencing on an image. We therefore use a modii ed
version of the function, which allows an image to be referenced to an
arbitrary rectangular coordinate system. Save the following code for this
modii ed version of the function
ginput
in a text i le
minput.m
.
function data = minput(imagefile)
% Specify the limits of the image
xmin = input('Specify xmin! ');
