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generated using the backward and forward views, resampled for 10 m. For assessment ends,
88 points were used, whose coordinates were determined by relative static positioning,
making use of double frequency GNSS trackers.
The authors initially made a planimetric accuracy assessment of an orthoimage generated
with 7 GCPs and SRTMDEM. The results showed that, even using a SRTM DEM, with 90 m
pixels, the orthoimage would be compatible with an indication for
class A for 1:25,000 scale
,
since the 40 points used in this initial assessment presented errors of up to 9.6 m, with SD of
2.1 m. Subsequently, the assessment was complemented using a DEM generated from the
Triplet PRISM data. The results were also satisfactory and similar to those obtained with
Cartosat1. The orthoimage presented planimetric accuracy compatible with
class B for
1:10,000 scale
, despite the authors' mentioning only attendance to scale 1 to 25,000 (which
was the target of the assessment), since all points presented errors up to 7.9 m and SD of 1.9
m. The altimetric accuracy of the
DEM
was compatible with
class A for 1:25,000
scale
since
92% of the assessment points presented errors of up to 5 m and SD of 2.3 m.
6. Scales 1:50,000 or less
6.1. SRTM DEM: Altimetric assessment
The DEMs generated from the data of this mission by NGA (National Geospatial
Intelligence Agency), NASA (National Aeronautics and Space Administration), have been
widely used in Brazil - as well as in other countries - for being free, of good quality and with
almost global coverage. Since its first divulging, in version 1, the immense potential for its
use was perceived, mainly in locations without altimetric data of better quality and coverage
in digital media. In function of the different versions available, four of them were chosen to
be evaluated:
Version 1: Original DEM with pixel resampled to 90 m, with negative values and many
areas without data, distributed by NASA. Additional information may be obtained on
the site http://www2.jpl.nasa.gov/srtm/;
Version 2: Includes additions made to version 1, with delimitation of a coastline,
elimination of negative values and reduction of areas without data, also distributed by
NASA. Additional information may be obtained on the site http://www2.jpl.nasa.gov/
srtm/;
Version 4: Derived from version 1, maintains a 90 m pixel, as well as some negative
values, but completes the areas without data. This version is divulged by CGIAR
(Consortium of International Agricultural Research Centers). Additional information
may be obtained at: http://srtm.csi.cgiar.org/SELECTION/inputCoord.asp;
Topodata: This version was generated and distributed by INPE in [18], with
reprocessing of version 1 data for the Brazilian territory, resampling the pixel for 30 m
by kriging. Additional information can be obtained at: http://www.dsr.inpe.br/
topodata/index.php;
The assessment was made in the same way for the four versions, with small variation in the
number of assessment points (between 90 and 92 points, depending on the DEM version) -
