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The location accuracy in remote
sensing can be expressed as RMSE (Root
Mean Square Error), which is derived
from the georeferencing algorithms that
rectify images to the map coordinates.
The RMSE is the square root of the
average of the square of the errors and
reflects the proportion or maximum or
minimum pixels number that the control
points of the image differ from the map
or from the reference control points.
Although,the RMSE not always reflects
the accurate location of all the pixels
in an image. The RMSE addresses only
the control points and only related to
the map. The most accurate way of
examining the location accuracy i= a
topographic control with GPS data, which
has a hig implementation cost.
The most common way to represent the
thematic accuracy or classification
generated by remote sensing is by an
error. matrix. An error... matrix: is... a
square arrengement of numbers belonging
to a particular category related to the
current category, as the one verifyed on
the soil. The coiumns usually represent
the reference data, while the lines
indicate the classification generated by
the remote sensing data. An error
matrix is an effective way to represent
the accuracy because the accuracy of
each category is fully described with
the inclusion and exclusion errors,
present. in the classification. The
error matrix can be used as a point of
departure for a series of statistic
descriptive and analytics measures.
The two most common thematic accuracy
measures use binomials probabilities or
agreement Kappa ratio. Binomial
probabilities are based on the correct
percentage, so that they do not separate
inclusion and exclusion errors. On the
contrary, the Kappa ratio gives a
different measure between the observed
agreement of two maps and the agreement
made by chance.
The Kappa advantages are that its
calculation considers the elements out
of the error matrix diagonal and that
the Kappa conditional ratio can be
calculated for individual categories.
In order to standardize procedures for
reports and for thematic statistical
maps, the error matrix shall present and
include the inclusion percentage error
by category, the exclusion percentage
error by category, the total correct
percentage, number of sampled points,
map accuracy and the statistic Kappa.
Final Product
The objective of most investigations
of remote sensing and Geographic
Information Systems is to produce a
product which gives important accurate
and quick information for scientists and
administrators. The product may have
several configurations, including
thematic and statistic summary.
The thematic maps may contain
statistic and dynamic information. A
statistic thematic map is produced by
analyzing the information collected in a
353
unique date, while a dynamic map must
produce the changes occured between
Succeeding observation dates.
In. order to reduce the error of the
final product there are important
procedures for these maps generation.
A substantial amount of error can be
removed if the reader is provided with a
complete cartobibliographic citation,
1.e., the genealogy or lineage of the
map products. In some remote sensing
Software packages there are methods for
tracking the processing flow for a
particular datafile. The general
proposition has been to create a
historical file by Ivsting all the
operations and parameters that have been
applicable to a data join. Other kinds
of error can be reduced by using good
cartographic design principles in the
generation of the map products, like the
legends.
Geometrical error in final thematic
map products can be inserted by the use
of base maps with different grades,
different national horizontal datum in
the Source materials and different
minimum mapping units that are, then,
resampled for a final minimum mapping
unit.
It is commanding the improving of map
legends that include cartobibliographic
information of the geometrical nature of
the original source material. This is
the only way to allow the readers to
judge the geometric accuracy of the
thematic maps final products.
The final map must be uniform in its
accuracy even being the addition of
information from several sources. It is
important for this map reader to know
which of these sources are reliable
thematic sources. There is a large
necessity of standardization of the
project and of the functions of the
reliable thematic diagrams.
The fundamental principles of the
cartographic projects must be followed
specially in the building of the classes
interval legends for thematic maps.
More and more, the remote sensing and
GIS information are presented in
electronic viewing device and excessive
classes intervals and poor colour
selection variations produce poor
cartographic communication on the CRT
visualizers.
While a lot of progress has been
done on the statistic thematic maps,
dynamic changing detection maps almost
always have poor legends. Too much
research is necessary to make possible
the report of the ocurred changes,
accurately, to the reader.
Several scientists, nowadays, have
superposed vectorial images with matrix
images. This powerful technique gives a
generic basic map that the reader can
use to guide and evaluate the vectorial
data. Unfortunately, there is no
standardization in relation to the
optimum viewing conditions for the
bottom image or to the optimum project
of the vectorial data. Researches are
necessary to standardize and provide, as
products, thematic maps which
incorporate a matrix/vectorial