Wednesday, 30 January 2008

Gravity and GPS Clock Speeds

Watched the Horizon programme "What on Earth is Wrong with Gravity?" last night. There was an interesting bit in it about GPS clocks and how gravity effects them. I must confess, particle physics is not my forte (to put it mildly!) and I got a bit lost with Einstein, time dilation and curved space time. My science teacher husband was engrossed, but I had a bit more background to assimilate before I really 'got' the issue with time and gravity.

Found this blog earlier which had a fascinating debate about GPS clock rates. I sort of kept up with the flow initially but lost it once red shifts came into play. I'm sure it's quite straight-forward really; it's just something I've never really thought about.

Monday, 28 January 2008

To Advise or Not To Advise

It was one of those days today when I offered advice and it wasn't taken, and I asked for advice and it wasn't given.

Our directors are currently having a debate about WGS84 Datum, which always worries me. I offered sensible advice to the person who was briefing them but I don't think it was taken. Very frustrating.

On the other hand, I needed advice about software programming for a project I'm running and I didn't get it in the way I needed it. I asked what I thought were the right questions but I didn't understand the answers.

Life is full of communication bridges isn't it? It's relating one persons' technical world to another. Far more easily said than done.

Thursday, 24 January 2008

Wire me to a Globe

I couldn't resist this purchase from a market in Cape Town earlier this month. It's fab!

Not only does it spin but it will be great for showing all those, as yet, geodetically unenlightened what lines of latitude and longitude are! I'm taking it into work tomorrow.

Later tomorrow I'm off home on the train with my girls. My elder daughter has just discovered a new game (honestly, not my idea) which she calls "grid references". The game apparently involves me giving her a grid reference and her working out the symbol, or me giving her a feature and asking her to give me the GR. She can't wait to play it on the train tomorrow with her OS map. Long live enthusiasm for maps! smile

Thursday, 17 January 2008

The Sahara Desert

When we were flying back from Cape Town my husband took some great shots of the Sahara Desert (click on them to find the lat and long).

I love these pictures. They so remind me of side scan sonar images.

Anyway, what is more impressive is that using a combination of BA's inflight map

and Google Earth he's geo-referenced them. I'll make a surveyor of him yet lol.

Geography Teaching in UK

It was sad, but no surprise, to read this article. I naturally loved geography at school (my Mum is a geography teacher, my Dad is very into maps and their enthusiasm rubbed off) but others aren't so inspired. sad

When I went round a local secondary school I was disappointed that the geography classrooms seem uninspired. I asked them about GIS but they said they didn't have much funds, it all going to science [my husband is a science teacher and retorted "they always say that!"]. There is so much you can do to enthuse children in geography. I talk maps and geography lots at home - now there's a thing - and the girls sometimes even seem keen.

Don't get me wrong, I'm not knocking geography teachers at all. If I thought I could do better I'd be one. But as surveyors we should be aware of education and offer to go in and take the odd lesson if needs be. I did at my daughter's primary school; the kids loved it but it was hard work! lol TSA and offer to lend surveying equipment which is a useful resource (NB, website is currently down).

Sunday, 13 January 2008

The Great Theodolite

Whilst I was in Cape Town over Christmas I had the honour to visit Richard Wonnacott at the South African Surveys and Mapping Directorate, based in Cape Town.

I was last there in 1995 and found they had one of the Great Theodolites. I couldn't resist a revisit.

Richard kindly showed me round their exhibition which contains far more than just the 36" theodolite. It's a treasure trove of historical survey instrumentation varying from a very early theodolite, to a Gunter's chain, a Millionar (I'd never heard of one of those before), an MRA1, Wild T3 and T4 (which funnily enough had the labels round the wrong way but no-one had noticed for years!) and some Maclear artifacts.

There was also an interesting exhibition on the Struve Arc, put together by the one and only Jim Smith.

More on the history of geodetic surveying in South Africa can be found here.

The piece de resistance for me was seeing the Great Theodolite.

In my piece for Geomatics World recently I called it the 'Everest Theodolite' and was politely e-mailed by Jim Smith who corrected my terminology. It's one of 6 Great Theodolites ever built. The first was built for Great Triangulation of Great Britain in 1787. After this 5 further theodolites were made. The second for the Board of Ordnance (cf Ordnance Survey) (1791), the third (c1797) for Swiss Surveying, the fourth (c1802) and fifth (1830) for the East India Company for the Trigonometrical Survey of India and the final one (1867) for India but relocated to the Cape in the late 19th century. I have my dates slightly adrift but I'm grateful to both Jim and Richard for sending me papers by Jane Insley (Science Museum) which I read with interest.

The only problem with revisiting this theodolite is that I now want to see the rest! They haven't all survived. The first was melted in a fire when the Ordnance Survey HQ, Southampton, was bombed in 1940. The second is in the Science Museum, London. Scraps of the third are in private hands. The fourth is in Dehra Dun courtesy of the Survey of India and the fifth in Calcutta. And the sixth is obviously in Cape Town. Looks like I need a trip to India. wink

Wednesday, 9 January 2008

Maclear's Beacon

Now this has to count as a pretty big trig pillar! Walked up Table Mountain last week with my family. It was a beautiful and steep walk up but by the time we reached 1000m we were in mist with a stiff wind. We literally didn't see Maclear's Beacon until we stumbled over it.

The plaque beneath it states
"This beacon was built as a triangulation station in December 1844 by Sir Thomas Maclear (1794-1879) in his survey for the verification and extension of the Abbe de la Caille's Arc of the Meridian. It was restored to commemorate the centenary on 14 July 1979 of Maclear's death. As Astronomer at the Royal Observatory he initiated the Geodetic Survey of South Africa."

A pretty impressive guy. More on him in my next post.

On the way across the top of the mountain came across another trig pillar. Or not.

Considering it was in a valley it made a fun signpost but a lousy trig pillar!

Saturday, 5 January 2008

I'm still here

For all those readers (reader?) out there I'm still around but just had difficulty uploading photos etc whilst in Cape Town. I'll slowly catch up over the next few days and regal you of tales of satellites, wire globes, misty trig stations and great theodolites. Bet you can't wait rolleyes