Graphics Programs Reference
In-Depth Information
The four corners of the image correspond to the pixels in the four corners of
the image that we store in a variable named
basepoints
.
basepoints(1,:) = [1,4200];
basepoints(2,:)= [1,1];
basepoints(3,:)= [4100,4200];
basepoints(4,:)= [4100,1];
The function
cp2tform
now takes the pairs of control points
input-
points
and
basepoints
and uses them to infer a spatial transformation
matrix
tform
.
tform = cp2tform(inputpoints,basepoints,'affine');
This transformation can be applied to the original RGB composite
naiva-
sha_rgb
in order to obtain a georeferenced version of the satellite image
newnaivasha_rgb
.
[newnaivasha_rgb,x,y]=imtransform(naivasha_rgb,tform);
Subsequently, an appropriate grid for the image may be computed. The grid
is typically defi ned by the minimum and maximum values for the longitude
and the latitude. The vector increments are then obtained by dividing the
longitude and latitude range by the array dimension and by subtracting one
from the result.
X = 36.096003 : (36.770406-36.096003)/8569 : 36.770406;
Y = 0.319922 : (0.958743-0.319922)/8400: 0.958743;
Hence, both images can be displayed for comparison (Fig. 8.4 and 8.5).
iptsetpref('ImshowAxesVisibl','On')
imshow(naivasha_rgb), title('Original ASTER Image')
figure
imshow(newnaivasha_rgb,'XData',X,'YData',Y);
xlabel('Longitude'), ylabel('Latitude')
title('Georeferenced ASTER Image')
grid on
The command
iptsetpref
makes the axis of the image visible. Exporting
the results is possible in many ways, such as
print -djpeg70 -r600 naivasha_georef.jpg
as JPEG fi le
naivasha_georef.jpg
compressed at 70% and at a resolution
of 600 dpi.
