Each of the frames of this animation were generated using PHP and the GD library.

1. The first triangle constructed is called a supertriagnle. It is an equalateral triangle that entirely contains the convex hull of the points to be triangulated. The vertices of this construction will be removed in the last step, leaving the triangulated network.
2. Points to be triangulated are added one by one. The list of points is ordered by their y co-ordinate.
3. The horizontal red line shown in the animation shows the advancing front. This is a horizontal line passing through the y co-ordinate of the most recent point added to the network.
4. Circumcircles pass through the three vertices of each triangle in the network. As each additional point is added to the structure, triangles who’s circumcircle contains the new point are identified. These circumcircles are drawin in red and their associated triangles highlighted yellow and removed.
5. New triangles are formed between the most recently inserted point and the segments of the void left after removing the flagged triangles.
6. The speed of the algorithm is improved by flagging all triangles who’s circumcircle is entirely behind the advancing front. Triabngles below this line no longer require testing in point 4 above. These are identified in green and then added to the pool of dark grey triangles that no longer need to considered with the addition of each new point.
7. After the final point is added, the vertices of the supertriangle and any triangles that share these vertices are removed.

The article described how The Seabellies, a relatively successful local band, were travelling to Melbourne to play a gig on Saturday night. Realising that the gig would coincide with Earth Hour, they planned to participate by turning off the lights at some point during their performance.

The Seabellies

Steph Setz, keyboard player, said the Seabellies would switch the lights off for at least one song and rely on a crowd armed with glow sticks to provide light.

The Newcastle Herald article received some particularly thought provoking comments from members of the public including this one from “James”:

The entire band drives/flies all the way to Melbourne and back in the space of 2 days and then claims to be supporting the principles behind Earth Hour? They even have the audacity to state that “every little bit, at work and home, counted when it came to cutting carbon emissions”. Astonishing hypocrisy.
Posted by James, 23/03/2010 3:39:54 PM

This got me thinking … about just how much carbon dioxide does a light bulb generate compared to travelling by car or air? With this question in mind, I used an online greenhouse gas emissions calculator to calculate the impact of the band’s travel to Melbourne.

What I found was that the band will generate about 1 tonne of CO₂ emissions if they drive two small petrol driven cars to Melbourne and back. Alternatively, if all 6 members chose to fly, they will generate about 3 tonnes of CO₂.

Compare this with emissions caused by lighting. The electricity that powers a modern light globe creates about 10 grams of CO₂ per hour. Driving the band to Melbourne and back would create as much emissions as leaving a light globe on for 100,000 hours! If they fly then they’ll generate as much CO₂ as a light globe would in 300,000 hours, or an astonishing 34 years of operation!

The relative impact of a single fossil fuel powered journey far outweighs any savings that could be made by switching off a few light bulbs for an hour. Unfortunately I think the relative magnitude of the contributions of various daily activities to ones carbon footprint is lost on most Australian citizens.

Air travel can generate a surprising amount of CO2 per journey

I should point out that this blog post is not intended to be critical of The Seabellies themselves. Indeed, my own band, Erin, has travelled similar distances for gigs in the past. For example, in March 2008 we travelled over 4000 km in two cars through regional NSW and Victoria to attend the Port Fairy Folk Festival. Additionally, I am very fond of international travel and dread to think what the carbon footprint of my history of air travel would be.

What concerns me here is the way that many Australians are seemingly unwilling to modify their lifestyle in order to reduce emissions. Even worse, I believe that events such as Earth Hour can make people complacent, leaving them with a sense that they have done something substantial to reduce their emissions. This false sense of accomplishment may make it easier for them to justify not making any additional changes to their lifestyle on the other 364 days of the year.

I think we should be using Earth Hour to highlight the impact of ALL our daily activities on our carbon footprint.

Reducing our greenhouse gas emissions is going to take more than just turning off some lights for an hour.

Seabellies image courtesy of Michael Spencer. Smokestack image courtesy of Colin Purrington. Boeing 767 image courtesy of superciliousness.

Passing through Quirindi on our way South #dishtour 11:44 AM Nov 22nd, 2009

The long drive home

Lunch at Muswellbrook RSL. Almost home. Day 4 of #dishtour 12:36 PM Nov 22nd, 2009

We visited SUSI, ACTA, MOPRA, ATNF, the AAT at the AAO, the UKST, the HAT-South (operated by the RSAA), inspected the FTS and even watched a RAVE. Since we seemed to visit acronym under the sun I thought I’d finish with a photograph this great T-Shirt worn by one of the scientists we met at the ATCA.

T-Shirt of the year

Day 3 of #dishtour. Heading to Narrabri to see the Sydney University Stellar Interferometer (SUSI). Hoping the air conditioning holds out. 7:34 AM Nov 21st, 2009

It was really hot this day, around 44 degrees or so. Everyone was happy to take advantage of air conditioning wherever it was available.

Chose a hell of a time to travel around central NSW looking at telescopes. 3 days in a row of 40+ temps. #dishtour 5:35 PM Nov 21st, 2009

As we were leaving Coonabarabran I spotted this motorcycle. Totally set up for touring I just can’t believe that such a vehicle could be controlled. Wouldn’t want to brake too quickly I’d imagine.

Brave Motorcyclist

It would take a brave and experienced motorcyclist to drive this I think: http://twitpic.com/qa1j9 Seen in Coonabarabran thismorning. 9:25 AM Nov 21st, 2009

The Mopra Telescope

On the way out of Coonabarabran we stopped at the MOPRA radio telescope.

MOPRA Telescope

The Mopra Radio Telescope has a 22-metre dish and is located in the Warrumbungle National Park near Coonabarabran. It is part of the Australia Telescope National Facility, operated by CSIRO. The name hails from the location of the facility close to Mopra Rock a geological formation overlooking the telescope.

The MOPRA radio telescope near Coonabarabran: http://twitpic.com/qam80 The detectors are cooled to -250 degrees with liquid helium #dishtour 11:43 AM Nov 21st, 2009

Mopra is controlled remotely from the ATNF facility near Narrabri.

Australia Telescope National Facility (ATNF)

The ATNF operates the Australia Telescope which consists of the Compact Array at Narrabri and the Parkes and Mopra radio telescopes. These telescopes can be used together as a long baseline array for use in Very Long Baseline Interferometry. The facility is located about 25km west of Narrabri in rural NSW.

As we approached the facility we were confronted with signs telling us to turn off all radio transmitters as they may interfere with the equipment.

Turn off all radio transmitters

Not easy to tweet while visiting radio telescopes. They are necessarily built in remote locations far from mobile towers. #dishtour 9:07 AM Nov 21st, 2009

We took refuge from the heat inside the visitors centre and ate soggy sandwiches.

Lunch at the Australia Telescope National Facility (ATNF) visitors centre

Australian Telescope Compact Array (ATCA)

After lunch we headed towards the Australian Telescope Compact Array control building. The ATCA is an array of six 22-m antennas used for radio astronomy.

Inside the Australian Compact Telescope Array control room

Our visit to the server room was welcome as it was cooled to about 10 degrees. Here we saw the banks of SUN computers that processed the data received by the dishes.

Inside the server room at the Australian Compact Telescope Array (ACTA) located near Narrabri, NSW: http://twitpic.com/qbxc9 #dishtour 5:12 PM Nov 21st, 2009

The view of these huge dishes perched on their tracks was an imposing sight. We paused on our way out to take a few more snapshots of these magnificant structures.

The Australian Compact Telescope Array (ACTA)

Sydney University Stellar Interferometer (SUSI)

Next up we headed towards the nearby Sydney University Stellar Interferometer (SUSI).

SUSI is a long-baseline optical interferometer. Interferometry is a technique that allows astronomers to improve the angular resolution of their observations. They can use this technique to determine the size of nearby stars. More about the interferometry technique on the SUSI webpage.

Sydney University Stellar Interferometer (SUSI)

Once inside the SUSI facility we were confronted with a huge array of optical equipment. Amazingly, the twin beams of light collected from the star being observed are recombined after matching the length of the light path to within one wavelength, causing the interference patterns required to complete the analysis. One wavelength of light equates to several hundred nanometres. For comparison, a sheet of paper is about 100,000 nanometers thick

Inside the SUSI Facility

The inside of the building was kept at a very constant temperature in order to achive the accuracy required. This was achieved by constructing a second shell inside the main building. The air between the two shells acted as an insulator to help minimise temperature fluctuations in the innermost compartment.

Thanks to the team at the Sydney University Stellar Interferometer for the fantastic tour and for their insight into the facility. #dishtour 5:38 PM Nov 21st, 2009

An Evening in Narrabri

After a very hot day at the ATNF we returned to Narrabri where several people from the tour chose to cool off in the hotel pool before dinner.

How retro, this motel in Narrabri has a VCR #dishtour 6:21 PM Nov 21st, 2009

The group assembled in the bar and chatted before dinner was served. After the sun set we assembled in the hotel car-park to look at the sky through a Meade LX200 telescope. Once again we observed the moons of jupiter and several other objects.

Looking at the moons of Jupiter after 5 beers in a motel carpark in Narrabri. Looking through a Meade LX200 scope. #dishtour 9:29 PM Nov 21st, 2009

Stargazing in Narrabri

Continue to Day 4 of the Beyond The Dish Tour

After an early start in Parkes we headed North towards Coonabarabran.

Day two of #dishtour. About to head to Coonabarabran for a tour of the Anglo-Australian telescope at Siding Spring. 7:26 AM Nov 20th, 2009

We spent nearly two hours in the cafeteria/gift shop at Siding Spring Observatory, consuming the time with chatter amongst the tour members and a wander through the various exhibits.

Lunch at Siding Spring Observatory

While eating lunch I tweeted one of my stellar puns.

Lunch at the Siding Springs Observatory cafe. The prices are astronomical, but the food is out of this world. #dishtour 12:24 PM Nov 20th, 2009

Siding Spring Panorama - Anglo-Australian Telescope on Right

Siding Spring Observatory panorama: http://twitpic.com/q7gas #dishtour 6:56 PM Nov 20th, 2009

View Larger Map

The Siding Spring Observatory is situated 1,165 metres (3,820 ft) above sea level in the Warrumbungle National Park on Mount Woorat also known as Siding Spring Mountain. Siding Spring Observatory is owned by the Australian National University (ANU) and is part of the Mount Stromlo and Siding Spring Observatories research school. There are currently 12 telescopes on site.

The Anglo Australian Telescope (AAT)

The first telescope we looked at was the Anglo-Australian Telescope, a 3.9 m equatorially mounted telescope. The AAT was comissioned in 1974 and at the time was one of the largest telescopes in the Southern hemisphere.

Inside the Anglo Australian Telescope (AAT)

Each day the dome housing the AAT is cooled to the temperature forecast for that evening at the Siding Spring site. This reduces exchange of air when the dome is opened at night resulting in a clearer view of the night sky.

We were lucky enough to be lead through the Anglo Australian Telescope by Astronomer-in-Charge, Dr Fred Watson.

Just had an amazing tour right through the Anglo-Australian Telescope: #dishtour http://twitpic.com/q6s5y 3:01 PM Nov 20th, 2009

Faulkes Telescope South

Our next stop was the Faulkes Telescope South (FTS). This fully robotic 2m reflecting telescope is a clone of the Liverpool Telescope. It is used for research as well as by school children around the world via the internet.

Faulkes Telescope South

Inside the Faulkes Telescope South at Siding Spring, NSW: #dishtour http://twitpic.com/q74f6 4:36 PM Nov 20th, 2009

The Faulkes telescopes can also be found on Twitter at @faulkestel.

UK Schmidt Telescope

The UK Schmidt Telescope survey telescope with an aperture of 1.2 metres and a very wide-angle field of view. The telescope was commissioned in 1973 and was designed to photograph 6.6 x 6.6 degree areas of the night sky on plates 356 x 356 mm.

Schematic of the UK Schmidt Telescope

More recently the photographic plates have been replaced with an array of fibre-optic cables strategically located so each one can gather the spectra of an individual star within the telescope’s field of view.

Computer controlling the placement of the optical fibres

The individual fibre-optic cables are placed with the help of a robot as seen in the image below.

Robotic placement of optical fibres

The UKST is currently conducting the Radial Velocity Experiment (RAVE). This is a survey that aims to measure the radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity) of up to one million stars near the Sun.

Skymapper

SkyMapper is a surveying telescope which is able to quickly and deeply scan the nighttime skies. It was comissioned so recently (became operational in May 2009) that it still had the “new-telescope-smell”.

The SkyMapper is a fully automated telescope, 1.3m in diameter with an 8-sq degree field of view. It will provide a deep digital map of the southern sky which will allow astronomers to study everything from nearby objects such as asteroids in our solar system to the most distant objects in the universe called quasars.

The Skymapper Telescope

The data taken by the SkyMapper telescope will be shared with astronomers around the world via the Virtual Observatory initiative.

Other Telescopes at Siding Spring

We continued on to visit a number of other telescopes at the Siding Spring Observatory:

HAT-South

The HAT-South is a project to search for transiting extrasolar planets in the Southern Hemisphere. It uses a network of wide-field telescopes to monitor hundreds of thousands of bright stars, searching for the characteristic dip in light that occurs when a planet passes in front of its host star.

2.3 Metre Advanced Technology Telescope

The 2.3 Metre Advanced Technology Telescope was housed in a building that could rotate on it’s axis.

Rotating Building Housing the 2.3m Telescope

Spinning building in the foreground with the Anglo-Australian Telescope in the background: #dishtour http://twitpic.com/q74p5 4:39 PM Nov 20th, 2009

Stargazing near Coonabarabran

After a long hot day trekking around the Siding Spring Observatory site we headed back to our hotel in Coonabarabran for drinks and dinner.

Arrival in Coonabarabran

Spirits were high after our epic day of telescope inspections and we were all keen to get our hands on some smaller scopes and see some of the objects we had been discussing for ourselves.

Back at Coonabarabran, heading out later tonight for some viewing at a private observatory #dishtour 6:52 PM Nov 20th, 2009

After dinner we boarded the bus again and drove to the Warrumbungle Observatory where we watched an interesting presentation about the objects in the night sky. There were about 6 different telescopes set up on a concrete pad, each one programmed to point at and track a different object in the sky.

Amongst the objects we saw were Jupiter and it’s moons, a globular cluster, the Pleiades and Neptune.

There were also two larger telescopes set up in domes. People were encouraged to bring along digital SLR cameras as they could be attached to these larger scopes. Below is one of the images taken by someone on our tour. It shows the M42 Nebula, a large area of hydrogen gas from which stars are born. It lies at a distance of 1500 light years away and is 15 light years in diameter.

Photo of M42 - The Great Nebula in Orion

Have just returned from an awesome night of stargazing. Saw Jupiter + moons, nebulae, Neptune etc etc. 6 telescopes operating. #dishtour 10:54 PM Nov 20th, 2009

We drove past the Warrumbungle Observatory on our way out of Coonabarabran the next day and I managed to snap this image out the bus window. The Telescopes on the concrete pad had been moved inside but the two domes housing the larger scopes are still visible.

Warrumbungle Observatory by day

Continue to Day 3 of the Beyond The Dish Tour

Average age of fellow #dishtour travellers seems to be about 60. Aging geeks abound. 7:38 AM Nov 19th, 2009

I needn’t have been worried however because the people on the tour turned out to be an interesting and entertaining group. As the nights progressed the conversations became more and more engaging. Interacting with the other group members was actually one of the highlights of the tour for me.

Lunch stop in Orange

We drove west out of Sydney. After a brief rest stop at Blackheath in the Blue Mountains we stopped at Orange for lunch where I was more than impressed with the selection of meat offered by the pub.

The steak selection at this pub in Orange is far better than my local butcher has to offer: http://twitpic.com/q1uiz #dishtour 12:25 PM Nov 19th, 2009

Quality selection of steak in a pub in Orange, NSW

After lunch we continued our journey west towards the Parkes Radio Telescope.

Parkes Radio Telescope

The Parkes Observatory, is a 64-metre Telescope used for Radio Astronomy. Yes, this is “The Dish” as featured in the movie of the same name. It’s an inspiring structure that sits in an unassuming sheep paddock about 20km North of the town of Parkes in central NSW.

Parkes Radio Telescope

We were taken on a tour through the entire facility. Unfortunately we weren’t allowed to walk (or play cricket) on the dish itself.

Just went on a ‘behind the scenes’ tour of the Parkes radio telescope: http://twitpic.com/q2uon #dishtour 5:46 PM Nov 19th, 2009

Inside the control room of the Parkes radio telescope: http://twitpic.com/q2uxb #dishtour Our tour guide: http://twitpic.com/q2v1z 5:50 PM Nov 19th, 2009

The Astronomers Room at Parkes Radio Telescope

Inside the Parkes Radio Telescope

Atomic Clock at the Parkes Radio Telescope

Did you know that “The Dish” was built at exactly 33 degrees south to make it easier for boffins with their slide rule calcs? #dishtour 5:53 PM Nov 19th, 2009

The modern computers and the atomic clock on the wall are a far cry from the paper and slide-rules originally used to aim the dish.

Whiteboard inside Parkes Radio Telescope

An Evening in Parkes

Later that night we looked at the moons of Jupiter through a replica of the telescope Galileo used 400 years ago. It was amazing that even through this relatively primative scope we were able to clearly make out the disc of Jupiter and the four “Galilean moons“, Io, Europa, Ganymede and Callisto.

Replica Galilean Telescope

Watching a man dressed as Galileo explain the minute details of his replica 400 year old telescope #dishtour 9:18 PM Nov 19th, 2009

Beyond The Dish Tour Group in Parkes

If you’re interested in making your own replica Galilean telescope I managed to find some detailed instructions on how to do it.

Continue to Day 2 of the Beyond The Dish Tour

Proposed Route

First stop was “The Dish”, Parkes Radio Telescope. From Parkes the tour made it’s way North to the Anglo-Australian Observatory at Siding Spring Mountain, Coonabarabran. We then headed to the Australian Telescope Compact Array and the Sydney University Stellar Interferometer at Narrabri before heading back to Sydney.

The trip was lead by of University of Sydney astronomer Dr John O’Byrne, who gave informative commentary throughout the tour.

Whenever I had the chance I wrote about what was happening through the popular microblogging site Twitter. Each of the tweets was tagged with the hashtag #dishtour so I could easily collate them at a later date. For example:

Day 1 of #dishtour. En-route to Parkes … 6:08 AM Nov 19th, 2009

Follow the links below for a detailed description of the four day tour that went “Beyond The Dish”.

• Day 1 – Parkes Radio Telescope
• Day 2 – Siding Spring Observatory
• Day 3 – Australia Telescope National Facility
• Day 4 – Heading Home

Web Of Life Website Thumbnail

Another option was to manually use the Print Screen key while each webpage is being shown in the browser, but with 6500 links in the directory, this would be very time consuming indeed, especially if I were to repeat the task periodically as I intend to.

After almost giving up on the idea I stumbled upon the Page Snapshot class at phpclasses.org. I found that code to be bloated and cumbersome, but it did lead me along a path that lead to a solution. The Page Snapshot class executes a command vie the exec command in PHP that requests a given URL in a web browser, it then waits a predetermined amount of time and takes a screen capture using Hypersnap. I used this same process, rewriting the code to suit my needs.

Hypersnap can be invoked via the command line and the file save format and capture area can be specified via command line options, making it a suitable tool for my needs. Used in conjunction with NMBot my screen capture process obeys robots.txt rules.

Website Thumbnail for the Beach Hotel Merewether

My PHP script allowed 20 seconds for all of the pages elements to be rendered, so the entire process took about 36 hours to complete. The thumbnails will be used on the Newcastle Music Directory website in the near future.

Here’s a video showing the first 4000 or so thumbnails:

Edit – April 2010: I never ended up using the thumbnails on the site.