International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B4, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
Forest. Figure 1 shows study area and the amount of points used 
in this assessment. 
  
  
o 1 2 = 
Figure 1: Study area location and points used in the assessment 
  
  
  
1.3. Cartosat-1 
Cartosat-1, also called IRS-P5, is an Indian satellite, launched 
on May 5th, in 2005 and it presents the capability of acquiring 
along track stereo images in panchromatic band. Its sensor 
presents a spatial resolution of 2.5 meters and radiometric 
resolution of 10 bits. Stereo pair is acquired in 2 different 
angles: 26" (forward view) and 5? (afterward view), which 
makes it possible to obtain a B/H ratio of 0.62. 
2. MATERIALS AND METHODS 
2.1. Field Survey 
For this assessment it was necessary to determine coordinates 
for 39 (thirty nine) points to be used in the geometric modeling 
process and other points to be used in the accuracy evaluation. 
All coordinates were determined in field trips using GNSS 
single frequency (Ll) receivers, through static relative 
positioning, registering data each 1 second during 30 minutes, 
obtaining a minimum of 1,500 epochs, for a distance between 
base and rover receivers not larger than 20 kilometers. All these 
values are according to Brazilian Institute for Geography and 
Statistics (IBGE) specifications. In this work comparison results 
refers to the Brazilian standard specifications (PEC) for 
classification of cartographic bases. 
2.2. DEM and Orthoimage Generation 
Cartosat-1 stereo pair (Path / Raw: 1814 / 0498) used in this 
assessment was acquired in May 23 2009, with the orthokit 
processing level, with RPCs (Rational Polynomial 
Coefficients). Cartosat-1 DEM and orthoimage were generated 
in PCI Geomatica Orthoengine 10.2, using RPCs. In order to 
improve results it was also used 7 (seven) GCP (Ground 
Control Points) and 8 (eight) Tie Points. The heights of Tie 
Points were obtained using SRTM DEM. Final RMS was below 
2.5 meters. 
For DEM generation, data was resampled to 5 meters when 
Epipolar Images were created and resampled again to 10 meters 
during DEM generation. Orthoimage was generated with the 
nominal spatial resolution of the raw data: 2.5 meters. 
2.3. Planimetric Evaluation 
The planimetric evaluation was done comparing coordinates of 
30 (thirty) Checkpoints (not used on the DEM and orthoimage 
generation process), which spatial distribution was presented in 
figure 1, and its homologues on the orthoimage. Most of 
Checkpoints were determined in intersections between roads or 
streets (figure 2). 
    
   
Check Point observed in the orthoirmage 
  
Check Point or terrain 
Figure 2: Example of a Check Point 
Difference between coordinates (in the orthoimage and on 
terrain) were calculated, obtaining the Euclidean distance which 
was considered an error and the errors were analyzed 
considering the specifications of PEC: at least 90% of the points 
used in this evaluation should present errors smaller than values 
presented in table 1. 
2.3. Altimetric Evaluation 
For this evaluation it was used 32 (Thirty two) Checkpoints, 
which spatial distribution was presented in figure 1. Altimetry 
evaluation was done comparing heights of the 32 Checkpoints 
with the value obtained in the GNSS survey plus the difference 
between ellipsoid and geoid in each point. Again results were 
analyzed considering PEC specification, which limits for error 
and standard deviation for altimetry are presented in table 2. 
3. RESULTS 
In General, results may be considered quite good and they are 
according to results observed on evaluation of equivalent 
sensors like PRISM (Barros ef al. 2009). Results are presented 
separately, according to the kind of evaluation. 
3.1. Planimetric Evaluation 
Considering the errors estimated for the 30 points used in the 
assessment, as well as the standard deviation observed (2.651 
m), this orthoimage presents planimetric accuracy compatible 
with the specified for class A of the scale 1:10,000, whose 
tolerance is 8 meters and the standard deviation limit is 5 
meters. We also calculated the Circular Error for 90% of the 
points (CE90), obtaining 5.56 meters. Table 3 presents the 
percentages of Checkpoints ^ presenting error till the limits 
specified for each accuracy class for 1:10,000 scale. 
  
Tolerance Checkpoint Percentage 
Class (meters) Number (90) 
  
  
  
  
  
  
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