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A Presentation for the 8 th semester Project Work 2 Entitled Extracting Stars from Sky Images: Applications to TAUVEX/ASTROSAT Being carried out at Indian Institute of Astrophysics By Sindhu Ravishankar 1PI01CS103 Sneader Sequeira 1PI01CS104 Sourav Basu 1PI01CS105

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A Presentation for the 8th semester Project Work 2

Entitled

Extracting Stars from Sky Images: Applications to TAUVEX/ASTROSAT

Being carried out at

Indian Institute of Astrophysics

By

Sindhu Ravishankar 1PI01CS103

Sneader Sequeira 1PI01CS104

Sourav Basu 1PI01CS105

Varun Sarin 1PI01CS113

Feb’05 – May’05

DEPARTMENT OF COMPUTER SCIENCE

PES INSTITUTE OF TECHNOLOGY,

100 FEET RING ROAD,

BSK-III STAGE,

BANGALORE – 560 085


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TAUVEX

  • Satellite to be launched by India as part of it’s developing space program

  • India’s first multi-wavelength astronomy satellite

  • Part Telescope - part communication satellite

  • Project related to the telescope aspect of the satellite


Software for tauvex l.jpg
Software for TAUVEX

  • IIA is developing ASTROJ.

  • Various algorithms and tools are provided

  • The first module that we developed is the point source algorithm

  • Original algorithm provided by European Southern Observatory


Point source algorithm l.jpg
Point Source Algorithm

  • Stars are usually point objects that are easily detected and distinguished by our eyes

  • But when placed on film, they tend to spread and form spheres called as Gaussian Surfaces

  • Discrepancies may arise.

  • Hence an algorithm is present that allows us to individually trace and label all point objects in the image


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Unique features (Design)

  • FITS images processed

  • Integration of various detection methods

  • Additional tools to fine tune output


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FITS Images

  • Flexible Image Transport System

  • Entirely new format of images

  • N-dimensional, goes beyond standard images

  • Format [PICTURE]


Data flow diagram l.jpg

Default Values

FITS Image Display

Main Process

User

Setting Smear, FinePos, FWHM, PHOT and Detected Method Flags and Values

Program Directed Graphical Output

Textual Output with X,Y coordinates,Median values

Data Flow Diagram


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Detection methods

  • Two different detection methods can be used :

    • Kappa Sigma method

    • Squares method

  • Objective in both is to detect point objects and store in the respective structure.


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Kappa Sigma Method

  • Bright objects are detected when:

    1. Peak is greater than threshold

    2. Cover a surface of at least of 3x3 pixels.

  • Smearing option available for images covering smaller area.

  • Look for signals 2 deviations above median pixel value.


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Process

1. Smearing (optional)

2. Binary mapping

3. Perform binary morphological erosion to remove bad pixels.

4. Apply flood fill algorithm

5. Fine positioning (optional)


Squares method l.jpg
Squares Method

  • standard deviation filter applied to the image

  • make the bright points appear like squares

  • squares image used as a mask to detect objects

  • morphological closing applied and remaining objects registered


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Additional tools provided

  • FWHM calculation

  • Fine positioning

  • Photometry calculations


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FWHM Calculation

  • Full Width Half Maximum

  • Used as a standard to measure the width value of Gaussian surfaces

  • FWHM flag set to toggle working


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Fine Pos Calculation

  • A type of filtering mechanism that treats bright peaks like bright squares

  • For each found peak position:

    • Calculate median pixel value

    • Compute barycenter using background

  • Limitation: all peaks must be of similar size


Photometry calculation l.jpg
Photometry calculation

  • Uses principles of photometry to investigate a star’s

    • Magnitude

    • Color

  • MAGNITUDE gives relative idea of its luminosity and distance

  • COLOR gives surface temperature


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Graphical user Interface

  • The following GUI elements have been incorporated in our project:

  • JFrame

  • JPanel

  • JMenu

  • JMenuItem

  • WindowListener

  • WindowAdapter

  • MouseListenerMouseMotionListener

  • JButton

  • ActionListener

  • Ellipse2D.Double

  • JSlider

  • JTextArea

  • MouseMotionAdapter


Output l.jpg
Output

  • The structure detected keeps count of the number of detected objects after the kappa sigma or squares method is initiated.

  • For all the objects detected, the following is done

  • 1. The x and y coordinates are obtained

  • 2. Ellipses are drawn on the screen corresponding to these values


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Conclusion

  • Provides astrophysics tools with advantages of programming in Java

  • Is an important tool that is useful for astronomical purposes

  • Is a crucial part of a series of tools to be used for data and image validation



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