[gnuastro-commits] master 48edcd91 13/39: Book: tutorial of zero point; preparing images for using the script

[Mohammad Akhlaghi]

branch: master
commit 48edcd91da53130724495a62b4520bdbf932e5ff
Author: Elham Saremi <saremi_elham@yahoo.com>
Commit: Mohammad Akhlaghi <mohammad@akhlaghi.org>

    Book: tutorial of zero point; preparing images for using the script
    
    Until now, I wrote an introduction for this tutorial.
    
    With this commit, I started to write the first subsection named "Using the
    image as a zero point reference". In this step, I selected two images of
    SDSS as a reference and an image of J-PLUS to find its zero
    point. Downloading and preparing of data in this step are written.
---
 doc/gnuastro.texi | 56 +++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 50 insertions(+), 6 deletions(-)

diff --git a/doc/gnuastro.texi b/doc/gnuastro.texi
index a2715716..fe2d38e0 100644
--- a/doc/gnuastro.texi
+++ b/doc/gnuastro.texi
@@ -629,13 +629,17 @@ MakeCatalog
 
 * Detection and catalog production::  Discussing why/how to treat these 
separately
 * Brightness flux magnitude::   More on Magnitudes, surface brightness, etc.
-* Photometric calibration zeropoint:: Calculating zeropoint of images
+* Photometric calibration zero point:: Calculating zeropoint of images
 * Quantifying measurement limits::  For comparing different catalogs.
 * Measuring elliptical parameters::  Estimating elliptical parameters.
 * Adding new columns to MakeCatalog::  How to add new columns.
 * MakeCatalog measurements::    List of all the measurements/columns by 
MakeCatalog.
 * Invoking astmkcatalog::       Options and arguments to MakeCatalog.
 
+Photometric calibration zero point
+* Using the image as a zero point reference
+* Using the catalog as a zero point reference
+
 Quantifying measurement limits
 
 * Magnitude measurement error of each detection::  Derivation of mag error 
equation
@@ -24609,14 +24613,14 @@ If you need to warp or convolve the image, do it 
@emph{before} the conversion.
 
 
 
-@node Photometric calibration of images with finding zeropoint, Quantifying 
measurement limits, Measuring elliptical parameters, Brightness flux magnitude, 
MakeCatalog
-@subsection Photometric calibration of images with finding zeropoint
+@node Photometric calibration of images with finding zero point, Quantifying 
measurement limits, Measuring elliptical parameters, Brightness flux magnitude, 
MakeCatalog
+@subsection Photometric calibration of images with finding zero point
 
 As described in @ref{Brightness flux magnitude}, to convert astronomical data 
pixel values from counts to energy/time (physical units such as Janskys), we 
need to know the zero point of the image.
 This conversion is necessary to can compare two images independent of 
instruments that were observed with them.
 Actually, the zero point is used to calibrate an astronomical image to the 
standard state.
 
-To find zero point, it is common to use photometric systems with defined zero 
point such as some images or catalogs.
+To find the zero point, it is common to use photometric systems with defined 
zero points such as some images or catalogs.
 For example, the SDSS data can be a good reference for finding zero point in 
optical and 2MASS data for near infra-red images.
 The general outline of the steps that we use to estimate zero point in an 
image is given below:
 
@@ -24624,10 +24628,10 @@ The general outline of the steps that we use to 
estimate zero point in an image
 @item
 Download of Gaia catalog using Gnuastro’s Query program (see @ref{Query}) to 
determine correct coordinates of stars in the image.
 @item
-Select of reference image or catalog and download of it.
+Select of reference image or catalog and download it.
 @item
 Aperture photometry with MakeProfiles (see @ref{MakeProfiles}) and MakeCatalog 
(see @ref{MakeCatalog}); a complete tutorial is in @ref{Aperture photometry}.
-If an image is selected as a reference for finding zero point, aperture 
photometry should be done in the same way for it.
+If an image is selected as a reference for finding the zero point, aperture 
photometry should be done in the same way for it.
 @item
 Match catalogs (see @ref{Match} and also a tutorial in @ref{Matching 
catalogs}) to obtain differences of magnitudes in two catalogs and estimate 
zero point value.
 @end enumerate
@@ -24638,6 +24642,46 @@ Here we have a tutorial on how to use 
@command{astscript-zeropoint}.
 This tutorial is divided into two parts to cover both of using image or 
catalog as reference data.
 
 
+@node Using the image as a zero point reference, Using catalog as a zero point 
reference
+@subsubsection Using the image as a zero point reference
+
+First, let's find the zero point for a single exposure image from the 
@url{https://www.j-plus.es,J-PLUS survey} based on an SDSS reference image 
@url{http://www.sdss.org/, Sloan Digital Sky Survey} with a zero point of 22.5 
mag.
+With the commands below, you can download an image such as one used in 
@ref{Moire pattern and its correction} from J-PLUS dataset in the r (SDSS) band 
and then crop the center part of the image to speed up the analysis in this 
tutorial.
+
+@example
+## Download a single exposure image from J-PLUS dataset.
+$ jplusdr2=http://archive.cefca.es/catalogues/vo/siap/jplus-dr2/reduced
+$ wget $jplusdr2/get_fits?id=771463 -Ojplus.fits.fz
+
+## crop the center part of image with the sky coordinates.
+$ astcrop jplus.fits.fz --center=107.7263056,40.17544223 \
+          --width=0.6 --output=jplus-crop.fits
+@end example
+
+Although we cropped the J-PLUS image, it is still very large in comparison 
with SDSS image.
+So let's download two SDSS images in the region of J-PLUS cropped image for 
having a more accurate result.
+
+@example
+## Download two SDSS images in r filter and decompress it.
+## (Bzip2 is not a standard FITS compression algorithm).
+$ sdssbase=https://dr12.sdss.org/sas/dr12/boss/photoObj/frames
+$ wget $sdssbase/301/6509/5/frame-r-006509-5-0115.fits.bz2 \
+       -O sdss1.fits.bz2
+$ wget $sdssbase/301/6509/5/frame-r-006573-5-0174.fits.bz2 \
+       -O sdss2.fits.bz2
+@end example
+
+
+
+
+
+
+@node Using the catalog as a zero point reference
+@subsubsection Using the catalog as a zero point reference
+
+
+
+