[ Home ] [ Up ]

Creating a Full Sky Star Map

This tutorial looks at the method I used to create this full sky star map. Sections of sky are rendered in HNSKY. These are then transferred to Photoshop via screen grabs, cropped and saved to RGB TIFFs for stitching with Panorama Tools.

Setting up HNSKY

There are a few adjustments that need to be made to HNSKY before you begin.

File > Settings

Set your latitude and longitude to W0°  N90°.  If you don't, all images will be tilted to match their appearance in the sky at the longitude that you specify.  While it doesn't matter from a technical point of view, it does make it much easier to work with the images later.
You can turn off most of the extraneous display options from the screen menu. For the others, you can simply make them black.
  1. Set the horizon line and text to black (just click on them and then select a colour)
  2. For the polar images, a cross will be displayed at the pole regardless of whether the grid is turned on or off.  For the polar images, set the grid colour to black, but as I also make a set of images with grids and constellations showing, I set this back to green after rendering the polar images.

Screen

  • Turn off everything in this menu.
  • In the projections section select "Azimuthal equidistant projection" (default)

Screen > Instruments

  • Turn them all off

Objects

Stars

  1. Set Boldness and Density to maximum
  2. Make sure there is no tick next to:
    • Name all stars
    • Activate USNO
    • Activate GSC
  3. Make sure Stars is ticked and increase the maximum magnitude to 20
  4. Select TYC for the Tycho2+ data set.

Deep Sky

Unselect all available options

The only other thing to decide on is the field of view (FOV) to render for each tile of the map.  I used 1100 arcmin and the following coordinates for my tiles.

DEC 0 +/-15 +/-30 +/-45 +/-60 +/-75 +/-89.9*
RA              
0 + + + + + + +
1 + + + +      
2 + + + + +    
3 + + + +   +  
4 + + + + +    
5 + + + +      
6 + + + + + +  
7 + + + +      
8 + + + + +    
9 + + + +   +  
10 + + + + +    
11 + + + +      
12 + + + + + +  
13 + + + +      
14 + + + + +    
15 + + + +   +  
16 + + + + +    
17 + + + +      
18 + + + + + +  
19 + + + +      
20 + + + + +    
21 + + + +   +  
22 + + + + +    
23 + + + +      

* I used 89.9 instead of 90 as this produces a "level" image without requiring any brain strain.  Using 90° rotates the image to compensate for the time of day and I couldn't be bothered figuring it out.

There's a lot of overlap, and at my highest screen resolution that's enough for a 22,000 x 11,000 pixel panorama. Overkill for my full map but it also provides images for high resolution sections of sky. Before starting to acquire screen grabs I'd recommend setting up a basic action in Photoshop as it takes out a lot of the tedium.

Creating a Photoshop Action.

  1. Maximise HNSKY
  2. Do a screen grab [ALT] + [PrintScrn]
  3. Start Photoshop and create a new image.

The dimensions of your screen grab should be automatically entered. This image will act as a temporary storage area for your screen grabs. now to create the Action

  1. Start recording a new action.
  2. Paste the screen grab into the image
  3. Flatten the image
  4. Select the area of sky, excluding the toolbars and window borders
  5. Copy the selection
  6. Create a new image and name the file to indicate the coordinates of the tile e.g. 13+45 for RA 13hr Dec +45°. Pad single digits so the images sort correctly. Turn the dialog ON for this step after you have finished recording.
  7. Paste
  8. Merge Layers
  9. Save the image (but don't edit the file name)
  10. Close the image
  11. Stop recording
  12. Assign a shortcut key to the action and remember to turn the dialog ON for step 6.

Acquire the Tiles

You are now ready to begin the tedious task of acquiring the tile images.  Switch to HNSKY and pres [CTRL] + [M].

  1. Enter your FOV in here
  2. Then enter your coorinates
  3. Click OK and do a screen grab [ALT] + [PrintScrn]
  4. Switch to Photoshop and hit the shortcut key for your action and repeat ad nauseum until your finished.

Stitching the Map

You'll have to wait for this section until I finish mine...  But it involves a few basic steps in PTGui/Panorama Tools including

  1. Fine tuning the fov of your tiles
  2. Positioning the tiles
  3. Stitching the final map

Here is the PTGui script I'm using (stitching should finish tomorrow!). It may work for you, but it may not...  a deviation of as little as 0.05° in the fov of the "lens" will generate significant errors.  It's possible to increase the panorama dimensions but you'll need a lot of RAM to open it in Photoshop.

Here's a small sample of what is produced (with a small error in the lower right quadrant due to a duplicated tile)

[ Home ] [ Up ]

This page, its contents and style, are the responsibility of the author and do not represent the views, policies or opinions of The University of Melbourne. All photographs © Ben Kreunen 2000

Ben Kreunen <bernardk@unimelb.edu.au>
Department of Pathology
Last modified: 13-Aug-2003