Triangulation pillars

While the Thai news - at least in my filter bubble - is full of coverage and speculation of the disappearance of a brass plaque in Bangkok, I'd like to feature a kind of plaques which can be found all over the kingdom, though I so far had only stumbled upon two of them.

The one displayed in the posting is found in Wat Amarin (วัดอมรินทรารามวรวิหาร), an old temple right next to the Siriraj Hospital. Sadly most of the temple ground is used as parking lot for the hospital, but the temple buildings are still a nice view. I went there last year to photograph a lot, as the site is listed as a historic landmark by the Fine Arts Department, however not yet officially registered by a publication in the Royal Gazette. And as last year the Wiki Loves Monuments only covered the published sites, the photos are still unprocessed on my hard disc. So while strolling around the temple ground, I noticed that not really spectacular marker stone - in fact very similar to those found at the province halls in all(?) provinces.

As the plaque is bilingual, its easy to recognize that these kinds of pillars are triangulation points used for mapping purposes. These pillars are erected by the Department of Lands, a subdivision of the Ministry of Interior. Named "Survey Mark" or หมุดหลักฐานแผนที่ (Mut Lak Than Phaen Thi - Major Mapping Pin), all I was able to find about them in Google was the guideline on how these pillars are to be built, also in the Royal Gazette there's only the 1936 law on the survey marks and its amendment in 1958. While for example for the UK some enthusiasts collected the location of all the trig points, I haven't noticed anything like that for Thailand during my short web search. If anyone wants to start such a collection, I'd certainly share my two points...