Geography Reference
In-Depth Information
study area covered the cities of Uberlândia, Indianópolis and Araguari, state of Minas
Gerais, in Southeast Brazil. The topography of this area is less mountainous with height
differences not exceeding 400 m.
The results indicate that the orthoimage presents a planimetric accuracy equivalent to the
class A of scale 1:50,000
, since 90% of the assessment points presented errors of up to 21.7 m
(already including the external error of the orthophotos - of up to 12.5 m), with standard
deviation of 3 m. The authors of the referred work emphasize that the assessment only
focused on geometry, like the remaining assessments here presented.
6.4. Landsat 7 ETM+: Planimetric assessment of the orthoimage
This assessment was the first research on the geometric accuracy of remote sensors carried
out in 2004, by Laboratory ESPAÇO, with the specific purpose to obtain the planimetric
accuracy of the Landsat images when orthorectified using the SRTM DEM (a novelty at that
time). Despite being a quite well-known sensor, we consider its inclusion in this chapter
appropriate for historical reasons and for its resemblance with the TM images from Landsat
5. Presently (2012) Brazil is concluding the updating of reference maps in the scale 1:250,000
using TM sensor images as main input.
Orthoimage was produced from the band 3 (red) of a scene (Path/Row 218/076) of sensor
ETM+ (Enhanced Thematic Mapper Plus), Landsat 7 satellite, acquired in August 1999, with
processing level 1G. Orthorectification was made with Orthoengine 9.0, by PCI Geomatics,
using 10 ground control points (GCPs) - whose coordinates were determined by a
navigation GPS (C/A - Coarse Acquisition Code) - and SRTM DEM version 1 (90 m pixel).
The choice for the navigation GPS was due to the ETM plus image characteristics - 30 m
pixel - and the lack of availability of single or double frequency trackers at that time.
In the planimetric accuracy assessment of orthoimage from Landsat 7 ETM+ only 4
assessment points were used, with coordinates determined by relative static positioning,
through single frequency GNSS receivers. It was chosen to work with a small number of
points for the assessment, but to determine their coordinates with greater accuracy.
The study area corresponds to the part of the municipality of Angra dos Reis, in Rio de
Janeiro, Southeast Brazil. Relief is mountainous in most of the scene, with height differences
over 1,000 m, for being part of the Serra do Mar Range. The prevailing vegetable cover
consists of tropical forests, with presence of grasses/pastures in some areas.
It was observed that the 4 assessment points presented positioning errors of up to 70 m with
an SD of 13 m. The results obtained suggest that the orthoimage presents a planimetric
accuracy compatible with the specification for a
class B for 1:100,00 scale
.
6.5. SPOT 4: Planimetric assessment of the orthoimage
Likewise as in the assessment of the Landsat Orthoimage, this was one of our first
planimetric accuracy assessments. The SPOT 4 images were renowned as having a very
