Lunar Parallax Demonstration Project
LPDP - How It Was Done
Image Handling
Each 01h20m UT image captured on the 9th November 2003 was analysed for stars in the
same frame. A vector overlay was created to mark the boundary of the Moon with a
circle, a cross (centered on the circle) to mark the position of the Moon's centre point and
a number of markers to identify the position of the stars. In addition, cross markers
were also overlaid on several identifiable lunar features (Mare Crisium, Tycho, Grimaldi).
These markers were used for orientation of the lunar disk in later stages of the
process.
Once the Moon's location had been marked, the image's had their levels adjusted
to make the background stars easier to pick out.
|
|
Supplied image
|
With overlay
|
A star chart was generated from a popular software planetarium application. This
chart showed the area covered by the parallax effect and a sufficient number of stars
to permit correlation with the vector overlays created from the contributor's images.
By taking just the individual overlays (one per 01h20m contributor) and matching them
against the star chart, a location map of the Moon at 01h20m on 9th November 2003 was
created.
It was always my intention to use a photograph of the area of the sky where the
eclipse parallax was happening as the background. Unfortunately, the weather here in the UK has been
truly dreadful for the past month and no such opportunity to take such a photo has arisen.
Hence, the background used in the final images has been artificially created
using the reference chart (it may be replaced with a real sky when/if the weather
clears!).
Using photo-editor software, each contibutor's image set was built up as
a number of image layers.
The background layer is used to provide a guide overlay for the vector markers (Moon and
stars). It also catches any over-sized masks! The overlay layer provides guidance
to where the actual Moon image should sit, how big it should be and it's orientation. This
layer is not kept in the final version. Once the overlay layer is in place the original
image can be brought in, dropped and rotated into position. A duplicate of the background
layer is created and brought to the top of the layer stack. An oversized mask is
made from the vector layer in the correct position. This mask, when applied allows
the original image to show through the upper layer in the correct position.
The overlay, image and mask layers are repeated with each of the contributor's images
used. By turning layers off and on, different contributor's images can be displayed and
saved off as a normalised (same background and field size) image for presentation
preparation.
Once the normalised version has been generated, the animated versions showing fixed
stars can be created (image sizes are identical).
The animations showing the stars moving is also created using the normalised images,
however, each image is moved so that the Moon disks exactly overlay each other.