%% $Date: 2012-07-06 17:42:54#$
%% $Revision: 148 $
\index{nav\_chk}
\algdescgeneral{Check navigation data for inconsistencies}
%
{ %%%%%% Algorithm name %%%%%%
nav\_chk
}
%
{ %%%%%% Algorithm summary %%%%%%
Tests navigation file (position and attitude) for inconsistencies and corrects them. The code is based on a HyMap *gps File.
}
%
{ %%%%%% Category %%%%%%
Quality Control
}
%
{ %%%%%% Inputs %%%%%%
*.gps file plus the number of image lines according to the ENVI header of the related image data.
The *.gps file is a multi-column ASCII file derived by HyVista Corp. proprietary software, which synchronises times and generates an output which is indexed by scan line number. The table below shows the list of parameters. \bigskip

\begin{tabular}{l l p{7cm}}
Parameters & Example & Description \\ \hline
Line & 1 & Scan line number \\ 
UTC Time & 48835.0462/20/5/2004 & Time of day in seconds/day/month/year \\
VME Time & 929386852.0 & Internal computer tick time in microseconds \\
IMU Time & 2048825953.1 & Internal IMU time in microseconds \\
Latitude & 48.03321015 & Decimal degrees (positive = north, negative = south) \\
Longitude & 11.28140200 & Decimal degrees (positive = east, negative = west) \\
Altitude & 2970.79892155 & Meters above MSL \\
Pitch & 0.22235917 & Decimal degrees (positive = nose up) \\
Roll & 0.54269902 & Decimal degrees (positive = right wing up) \\
Heading & 0.37774316 & Decimal degrees (positive = N-E-S direction, negative = N-W-S direction) \\
True Track & 1.00507651 & Decimal degrees (0 to 360) \\
Ground Speed & 72.90907700 & Meters / second \\
Sat & 5 & Number of satellites being received \\
DGPS & 1 & DGPS status: 1 = DGPS being received 0 = no DGPS received 
\end{tabular}
}
%
{ %%%%%% Outputs %%%%%%
status file $\rightarrow$ template+'\_status'

If applicable: corrected gps file

backup of original .gps $\rightarrow$ filename.gps\_original
}
%
{ %%%%%% Formula %%%%%%
test \& correct the following
\begin{itemize}
\item point or colon - separator in .gps => error catched in hymap\_read\_gps.pro corrected when re-writing the .gps-file anyway
\item \#lines in image  =  \#lines in gps

if too many gps-lines: truncate lines at beginning (like Hyvista does)

if too few gps-lines:  adding extrapolated lines at end
\item invalid start / end time: calculating average timestep \& using last relieable line
\item data gaps (indicated by identical time): interpolate info
\end{itemize}
}
%
{ %%%%%% Author %%%%%%
DLR-DFD
}
%
{ %%%%%% References %%%%%% 
EUFAR FP7 - DJ2.2.2 - Quality Layers for VITO, DLR, INTA and PML
}


