Geoscience Reference
In-Depth Information
Fig. 8.1
Image projection
and merging operations.
a
Warping includes ground
control points to georeference
an image.
b
In a mosaic
images of different
geographical extents are
merged.
c
Compositing
combines overlapping images
according to some rule
(averaging, maximum value,
etc.)
(a)
(b)
(c)
8.2 Resampling
Simple image processing software require images to be in the same coordinate system
for simultaneous visualization and processing. Others, including QGIS, support “on
the fly” reprojections where all images opened in the map canvas are automatically
projected to a common coordinate system (e.g., the one of the first image loaded).
However, you have to be aware that each projection involves a resampling step that
can alter the original data. It is therefore recommendable to limit the number of
reprojections to a minimum.
GDAL provides different resampling methods,
implemented in the utility
gdalwarp
(see Sect.
8.3
):
Search WWH ::
Custom Search