.. _wv_correct:
wv_correct
----------
An image taken by one of Maxar (DigitalGlobe) World View satellite cameras
is formed of several blocks as tall as the image, mosaicked from left
to right, with each block coming from an individual CCD sensor
:cite:`digital-globe:camera`. Either due to imperfections in the
camera or in the subsequent processing, the image blocks are offset in
respect to each other in both row and column directions by a subpixel
amount. These so-called *CCD boundary artifacts* are not visible in
the images but manifest themselves as discontinuities in the the DEMs
obtained with ASP.
The tool named ``wv_correct`` is able to significantly attenuate these
artifacts (see :numref:`ccd-artifact-example` in the
Digital Globe tutorial for an example). This tool should be used on raw
Digital Globe images before calling ``dg_mosaic`` and ``mapproject``.
It is important to note that both the positions of the CCD offsets and
the offset amounts were determined empirically without knowledge of
Digital Globe's mosaicking process; this is why we are not able to
remove these artifacts completely.
For PAN images, the WV01 and WV02 datasets are supported, for most TDI
for the forward and reverse scan directions. For WV03 PAN images, CCD
artifacts are less noticeable than for WV01 and WV02, and they are not
corrected at this time.
For multispectral images, only a few select TDI are supported for band
3 of WV02 data. If a certain combination of spacecraft/TDI is not
supported, the tool will print a warning and will write on output the
uncorrected input image.
The ASP source code repository has additional documentation and tools for how to
tabulate the corrections for the cases not yet covered by this tool.
Note for WV-2 images
^^^^^^^^^^^^^^^^^^^^
Maxar (DigitalGlobe) WorldView-2 images with a processing (generation) date
(rather than acquisition date) of May 26, 2022 or newer have much-reduced CCD
artifacts, and for those this tool will in fact make the solution worse, not
better.
ASP of version 3.3.0 or later (and any development build after 2023-06-21) will
automatically detect this and will not apply the correction (a copy of the input
image will be written on output). A warning will be printed in that case. This
holds for both PAN and multi-spectral images.
This scenario does not apply to WorldView-1, 3, or GeoEye-1.
Usage
^^^^^
::
wv_correct [options]