Survey Mark

[+vespax]

Since arriving in SA a month ago, and not having a car, I have had the great opportunity to walk alot. The weather has been nice lately, huh?

 

I have noticed a lot of Survey Markers in the streets. There are two types that I have observed, a square metal plate about 30x30 centimeters. And then a smaller type about 5x5 or so. They all have a what looks like a key lock on them. Do you need a special tool to open them up? I want to see what's in them, what they look like, but am also worried that there might be a law against opening them up. Anyone know?

 

Also, would it be possible to hide a micro in one of those boxes?

 

In the United States, and on geocaching.com, survey disks are called benchmarks. Does SA publish their survey disk info for the public to use? Could say, globalrat or geocacher.co.za publish them and we have an extra thing to look for.

 

Just thinking. Any thoughts?

[+Jors]

I am not quite sure what two types you are describing, but in South Africa, we use:

 

1) Trig beacons mostly on mountain tops ( a round white concrete pillar 1,2m high 400mm in diameter with a black square (400mmx400mm) steel vane, also 1,2m above the pillar). These have positional a accuracy of 10mm and height is accurate to within 100mm.

 

2) Town Survey Marks, (TSM's) being a 13mm brass pin set in concrete below ground level in a round cast iron box, 228mm diameter, normally in the tarred road surface. The 152mm lid has a square pattern on it, with a raised triangle in the middle indicating a survey marker, and can be opened without any special tools. The lid only rests on the collar, but its the sand/soil/gravel that prevents it from being opened easily. I normally only hit the lid hard a few times in the centre (Mr. Venter) with a hammer, which loosens the dirt, whereafter I lift the lid with a 10mm x 300mm round bar, inserting it into the 15x25mm slot. I've opened a lot of them in this manner, and never smashed one. Once I needed to dig out the marker because it was tarred over. Positional accuracy of these type is also 10mm, but in height they are accurately levelled to within 1mm (0,001m). In rainy season they are often filled with water, or just mud.

 

Have you seen any of these? All of them are numbered on a stamped copper/aluminium/stainless steel plate (25x75mm) on a 250mm chain inside.

 

The law ((Land Survey Act) only states that you are not allowed to destroy them without written permission, thus do feel free to open them and have a look inside.

 

3) Then there are height markers along the side of the (old) main roads between cities an towns. I have not seen these, but I know they exist. These only have accurate height values, but no usable positional value, and might thus be difficult to find.

 

From your description, I doubt that what you saw are survey markers, maybe we can clear that up with a more detailed description? Utilities, perhaps?

 

I have thought of hiding a micro in a Town Survey mark, but safety of the person opening it is of some concern, since most of them are in areas highly frequented by fast moving cars and other wheeled objects, but if you find a safe one, why not give it a go?

 

There are about? 28500 trig beacons in the country, but I have no idea on the number of TSM's.

 

Thinking is good ....

[+vespax]

Jors,

 

I think your description more accurately describes what I was trying to describe. That looks weird, to many descri.... in the sentence.

 

It sounds like you might be a surveyor or engineer since you know a bunch about these. I am glad to hear that I can open them up since there is one down the street from my front door that I will now try and open.

 

I have been meaning to go to or contact the directorate of survey and .....(can't remember the full name) to get some map data from. They are down the road in Observatory. I suppose they have info on these survey marks as well.

 

I may well find a remote one in a park perhaps and give it a try with a cache.

 

Thanks for the info. I am going to copy and paste it locally so I have it to refer to when the thread gets pushed down the list. Again, thanks for the info.

 

I will try and take a picture of each type and post it in here to make sure we are referring to the same thing.

[+warthog]

The TSMs sounds a great idea. Can someone maybe post a photo of these so that we can see what they look like. Closed and open to see what it looks like inside. Would be a nice alternative to caching to see how many of these we can locate.

[+warthog]

I received the following reply from an email sent to the Chief Directorate: Surveys and Mapping and once received will share/publish to everyone interested.

 

The co-ordinates you are requesting are available free of charge if supplied in digital form ie via email. I have passed your request on to Bronwyn McClement who is the manager of our sales division.

 

Regards

 

Richard

 

R T Wonnacott

Director : Survey Services

Chief Directorate : Surveys and Mapping

Private Bag X10

Mowbray

7705

SOUTH AFRICA

[AE_Rodney]

Can you post pics of the things you mean vespaxvespa.

[+vespax]

Will go out this morning and try and get a couple. Sorry for the late reply.

[+Jors]

I managed to get a few pics of the real thing.

 

The tape measure is extended 200mm

 

Though not clear on the photo's, the hole is at least 200mm deep.

[+vespax]

um.....

 

That looks different than what I am finding.

 

 

Tht is the large size one. There are smaller ones that look like this.

 

 

I forgot to get a reference on that one. If you make a circle with your two thumbs and pointer fingers, that is about the size of the disk.

 

These are in the Wynberg area of Cape Town. I wonder if there were different styles according to when they were placed, or some other reason to explain it. I tried to get the lids off of them, but I couldn't. I think I need to make some sort of tool to lift up once it is hooked under the lid.

 

I can't see in your pics, but is there a disk of some sort that contains data, or is it a metal point? How does the surveyor know which mark is which and the data coorresponding to it? Do they carry a book with the info in it?

 

Thanks, .......

[+Jors]

Eish...

 

Looks like it is the screenshot problem revisited.... Me sees nuttin...

 

On my pic, the aluminium plate at the end of the chain can be seen, on which a reference number is stamped. The numer is more for confirmation though, since surveyors know where these things are, and which ones they are going to use, and then they go out with the co-ordinates at hand. Not in a book, mostly already uploaded into the instrument/data logger. (it is darem the 21st century )

 

It's a metal point in the centre, to which the co-ordinates refer, the box only protects the copper pin.

 

I might be able to comment on your find once i've seen the pics...

[+Jors]

Posting vespaxvespa's pictures...

 

C.CC = City Council of Cape Town ?

[+GlobalRat]

Yes, I do have a full list of the TSM's and of all the trig beacons in the country. You can get a list from the directorate for free, they'll email them to you, but the format is not in WGS84 for the TSM's. I had the coordinates converted (thanks Jors).

 

The boxes with padlocks on them, well I did enquire to the directorate what's in them a few months ago, but never received a reply. However, if you come across one of these where the lock has been removed you are supposed to report it to the directorate of surveys so they can replace the lock and chain. Also if number has been removed or damaged.

 

They are essentially the same as the benchmarks in the US. These listings will move to Waymarking.com in future.

 

If anyone is interested, I'll add the files to my site for download.

[+vespax]

More investigating seems to be needed.

 

jors, got the email with the file. Will take a look at it in the next day or two. Have various GIS software, perhaps I can organize them and see what can be done with the file.

Edited October 30, 2005 by vespaxvespa

[Stefanoodle]

I requested the file of all the trig beacons in South Africa from the Directorate of Survey and Mapping in Mowbray when I was trying to calibrate some digital maps of South Africa, also free of charge from the Directorate. They sent me a text file the next day. As pointed out, though, the co-ordinates are in the South African Grid format, so after trying to convert them myself, using a bit of simple trigonometry, but assuming a spherical earth, I found I was often out by up to 400 metres. Therefore, I bought some software from Survey and Mapping for R50.00, and it does the conversion quickly and painlessly.

 

From what I can see, the text file contained only trig beacons, either on cylindrical concrete plinths, or on top of certain buildings, such as churches or water towers. None of the descriptions sounded like the town marks you guys describe. It would be interesting to have some of our TSMs listed in the benchmarks section of geocaching.com.

[+Jors]

The TSM's dont have published descriptions AFAIK, the detailed description only appears in the Old Land Survey Act, No 9/1927, and corresponds to my photo's earlier in this thread.

I have Ozi and Mapsource files for the Cape peninsula which I converted from the cleaned-up text file if anyone is interested.

 

TSM's are available CDSM for the following towns, for which I have only the text files:

atlantis , boksburg , bothavil , caledon , ceres , darling , durban , edenvale , ermelo, fortbeau , germisto , grahamst , groblers , harrismi , hermanus , johannes , ladismit, louistri , newcastl , parys , pietersb , plettenb , portshep , pretoria , richmond , sandton, somereas , SPRINGS , stanger , ALBERTON , swellend , tzaneen , upington , villiers , vryheid, wellingt , witbank , zeerust , centurion , bonnieva , barberto , beaufort , belfast , bethlehe, bloemfon , boshof , bredasdo , brits , calvinia , christia , colesber , ct_pen , deaar, dundee , eastlond , empangen , estcourt , ficksbur , fochvill , george , graaffre , greyton, greytown , harding , heidelbe , heilbron , humansdo , jamestow , jeffreys , kimberle , kingwill, kleinmon , klerksdo , knysna , kroonsta , krugersd , kuruman , ladybran , Ladysmit , laingsbu, lichtenb , lydenbur , malmesbu , marbleha , margate , melkboss , meyerton , michelled , middelbu, montagu , mooirivi , mosselba , nelsprui , nylstroo , onrusriv , oudtshoo , paarl , pieterma , pinetown, portalfr , porteliz , potchefs , potgiete , queensto , richards , robertso , rustenbu , saldanha , senekal , somerwes, springbo , st_helen , standert , stellenb , strand , tongaat , uitenhag , umtata , vereenig , vredenbu , vredenda, vryburg , welkom , westvill , worceste & zoar

[+GlobalRat]

have some of our TSMs listed in the benchmarks section of geocaching.com.

As far as I'm aware these are limited to US Benchmarks as part of a benchmarking project and the finds don't count.

 

Also, Benchmarks/TSM's will be moving off GC to Waymarking.com as far as I know.

[Royfamily]

These are Town survey marks for the City of Cape Town. The one photo has the number panted on the outside 3L18 and its coordinates are 50083.760Y 3763880.320

X and 71.394Z. They are used for mapping purposes. The main ones that we use for our Aerial photography have white crosses painted arounf them with the survey mark in the middle.

 

Allan