(almost) everything you wanted to know about using s2plot to visualise astronomy datasets

(Almost) Everything you wanted to know about using S2PLOT to visualise astronomy datasets CRICOS provider 00111D

Christopher Fluke

& David Barnes

“Those not properly initiated into the mysteries of visualisation research often seek to understand the images rather than appreciate their

beauty...” Al Globus & Eric Raible (1994)

Visualizaton at ATNF 2009 (Almost) Everything you wanted to know about S2PLOT... 2

What is Visualisation?

Science

Data

Visualisation System

Knowledge discovery

The process of creating (computer-generated) images in order to gain new understanding or insight into data.


Astronomical Data

Brunner et al. (2001):• Imaging data: 2D, narrow , fixed epoch• Catalogs: secondary parameters determined from processing

(coordinates, fluxes, sizes, etc). • Spectroscopic data and products (e.g. redshifts, chemical composition).• Studies in the time domain - moving objects, variable and transient

sources (synoptic surveys) • Numerical simulations from theory

Planning, data collection, reduction, comprehensionMany astronomical datasets have N > 3


The rest of this presentation...• What is S2PLOT?• Getting started• Geometry

• Points, lines, coordinates, labels, text• Spheres, cubes, polygons• Colour and colour maps

• Static versus dynamic geometry: S2PLOT callbacks• Billboards/splats• Handles• Nice fonts• Volume rendering, isosurfaces

• Other media• 3d-PDF, Web, s2slides


Introducing S2PLOT

• AIMto enable visualization-led scientific discovery

• BYmaking an easy-to-use programming library

• THAT WORKS ONthe astronomer’s desktop workstation

• AND WITHOUT RECOMPILATION ONadvanced display devices

• RESULTS2PLOT: Barnes et al., 2006, PASA, 23, 82 www.astronomy.swin.edu.au/s2plot (Version 2.4)


Key Features and Benefits

• Supports standard and enhanced displays

• Real-time interaction

• Mouse + keyboard navigation

• Static and dynamic data

• Runs on Apple/OSX, GNU/Linux and Windows (GNU/cygwin)

• C/C++, Fortran and Python

• PGPLOT-inspired programming interface


A Practical Example


A Practical Example

2-d views of multi-d data• Colour-colour

• Colour-magnitude


A Practical Example


Initialise

Create geometry lists

Register callback functions

Handle window events

Handle user events

Process callbacks

Draw geometry using OpenGL lists

S2PLOT Program Flow


An easy s2plot program (in C)


Comiple and Execute

• Configure your S2PLOT environment...

cbuild.csh s2example ./s2example


Programming Reference

http://astronomy.swin.edu.au/s2plot


Sample code for every function


PGPLOT versus Native functions


Example: Points and lines


Example: spheres and polygons


Example: text


Static versus Dynamic geometry

• Static geometry• Draw it once

• Dynamic• Redraw on every display refresh• Animation!• Advanced interaction: mouse click events, key presses, iPod• Geometry that depends on camera angle

• Callbacks


Billboards & Splats

• Billboards: (2-d) things which always face the camera• good for labels & markers

• Splats: billboards which are soft point-like textures (images)• visually appealing alternative to single-pixel points

star fields, stellar clusters• variable size and colour with good blending properties

simulated particle distributions thresholded, gridded volume data

• Billboards have to be redrawn whenever the camera moves, so they must only be created in a callback function.


Billboards & Splats: Example


Nice Fonts

• As in PGPLOT, the basic font in S2PLOT is a "Hershey" font• vector-based• functional & fast, but inelegant

• S2PLOT provides 2 better ways to create text labels• unsigned int ss2ltt(char *latexcmd, float *aspect);

uses LaTeX to generate a bitmap which is converted into an S2PLOT texture for you. (Requires a few environment variables to be set correctly - see ENVIRONMENT.TXT in S2PLOT)

nice for equations• unsigned int ss2ftt(char *fontfilename, char *text,

int fontsizepx, int border); uses the FreeType2 font engine to generate a bitmap which is

converted into an S2PLOT texture for you.


Nice Fonts: Example


Handles

• Handles provide user interaction• they can be displayed or hidden with Shift-S• your code can be alerted when a handle is clicked on• your code can be alerted when a handle is dragged

• Handles have:• a position in 3-d space, and a size (fraction of the screen)• a texture and colour for their "unselected" state• a texture and colour for their "selected" state

• You can make invisible handles and draw other geometry at their location if you want.


Handles (continued)

• Possible uses for handles:• select points in a displayed dataset• select galaxies or stars or planets in a visualisation• define a 3-d region (volume selection)• provide buttons and sliders and even menus

this is typically done in "screen coordinates" mode• allow users to define control points along a spline camera path• etc.


Isosurfaces and Volume Rendering

Data courtesy J.English


• Colour can enhance important features• Can exaggerate unimportant details• Try different colour maps

Colour maps

Computers generate colours through R G B combinations24-bit RGB = 16,777,216 (256³ or 224) colours


Other media

• 3-d PDFBarnes, D.G., Fluke, C.J. 2008, Incorporating interactive 3-dimensional graphics in astronomy research papers, New Astronomy, 13, 599

Fluke, C.J., Barnes, D.G. 2008, The Interactive Astronomy Textbook, Astronomy Education Review, 7, 113

• WebFluke, C.J., Barnes, D.G., Jones, N.T. 2009, Interchanging Interactive 3-d Graphics for Astronomy, Publications of the Astronomical Society of Australia, accepted, arXiv:0810.4201F

• s2slides: “PowerPoint”-style presentations


Where to next?

• Try some S2PLOT sample codehttp://astronomy.swin.edu.au/s2plot

• Take part in the hands-on workshop

• Talk to me about your data

(almost) everything you wanted to know about using s2plot to visualise astronomy datasets

Documents

easy s2plot program

practical examplealmost

data collection

spectroscopic data

imaging data

dynamic geometry

colour maps static

dynamic dataruns