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% Solve.tex
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% SatNOGS Optical Unofficial Guide
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% Copyright (C) 2022, Jeff Moe
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% This document is licensed under the Creative Commons Attribution 4.0
% International Public License (CC BY-SA 4.0) by Jeff Moe.
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\section{Plate Solver}
\label{sec:plate-solver}
\index{plate solver}
A ``plate solver'' will take an image of stars and detect the time and place
of the picture. There are two main steps:

\begin{enumerate}
 \item Extract stars from an image, such as a \gls{FITS} file generated by \texttt{stvid}.
 \item ``Solve'' the image of the stars in the image against vast databases of star images.
\end{enumerate}

See below for a list of software tools that detect/extract stars from
images (e.g. \gls{FITS}).

\begin{itemize}
 \item Source Extractor.
 \item XXX Kstars with ekos adds \texttt{Internal SEP}.
 \item XXX Kstars with ekos adds \texttt{Builtin method for solver}.
\end{itemize}
\index{Souce Extractor}\index{Kstars}\index{ekos}

See below for a list of plate solvers than can be used.

\begin{itemize}
 \item astrometry.net locally.
 \item astrometry.net Internet.
 \item astap.
 \item Watney.
\end{itemize}
\index{astrometry.net}\index{astap}\index{Watney}


\section{Source Extractor}
\index{Source Extractor}
\texttt{Source Extractor}, formerly \texttt{SExtractor} and some other names,
is an application to extract stars from images. The software has been
widely used for many years.

\url{https://www.astromatic.net/software/sextractor}


\section{astrometry.net}
\index{astrometry.net}
Astrometry.net is a website and software that can be run locally to solve
a plate of stars that has been extracted from \texttt{Source Extractor}. XXX
\index{Source Extractor}

% https://nova.astrometry.net/
\begin{figure}[h!]
        \includegraphics[keepaspectratio=true,height=1.10\textheight,width=1.00\textwidth,angle=0]{astrometry-web.png}
        \caption{nova.astrometry.net website.}
        \label{fig:astrometry-web-web}
        \index{astrometry.net}
\end{figure}

\fbox{
        \parbox{\linewidth}{
                \textcolor{red}{NOTICE:} \\
                Using astrometry.net online requires an account with non-libre services.
		The astrometry.net software can be installed locally to avoid this.
                \index{proprietary}
        }
}


\section{Star Databases}
\index{star database}
To use a plate solver, you will need star databases. They can get large.
The \texttt{stvid} application includes a basic star database.
XXX The \texttt{4200} series is also recommended.


\section{World Coordinate System}
WCS info. XXX


\section{Plate Solving with \texttt{stvid}}
Use the \texttt{process.py} scripts described at XXX to solve plates
with \texttt{stvid}.