Hearst Castle Mini Prism

Photo provided by Stanley King, Senior Land Surveyor, California Parks Department

The Hearst Castle is a 96-year-old landmark mansion located on California’s central coast, boasting impressive historical architecture and a dramatic seaside view. Despite being far from any large urban area, the mansion-turned-museum attracts millions of travelers each year.


Since the site became part of the California State Parks system in the mid-1950s, repeated exposure to earthquakes had weakened the decades-old tiling around the Neptune Pool––a large, elaborate swimming area made primarily of marble and slate.


To remedy the problem, a two-year renovation project was planned to make the necessary repairs. Tasked with managing quality assurance and control, surveyors from the California State Parks Department needed a way to establish highly precise survey control under difficult conditions.


The search for a highly accurate yet discreet survey solution


Surveyors from the Parks Department were confronted with a tough challenge.


Site owners were adamantly opposed to using any kind of survey equipment that would damage or deface the delicate historical structures on-site. At the same time, the project required extremely accurate surveying measurements––something most assume only large, intrusive equipment can provide.


With so many museum visitors passing through the area each year, site owners also needed any permanent equipment to be as discreet as possible.


After considering a handful of options for survey control, the Parks Department narrowed their search to two ideas:


  1. Reflective tape, or
  2. RSMP15 mini prisms

Hearst Castle Mini Prism

Photo provided by Stanley King, Senior Land Surveyor, California Parks Department

Parks Department surveyors evaluated the devices on size, discreetness, accuracy, and the amount of damage caused by installation.


While tape seemed like a possible option as it didn’t require invasive screw mounting, testing quickly revealed they couldn’t give the measurement accuracy that was needed for precise projects like this.


After testing the mini survey prism, however, surveyors were surprised to find the accuracy ability of the RSMP15 actually exceeded their initial expectations. Rather than screw-mounted larger prisms, these could be permanently glued into place and removed years later without leaving any trace behind.

Mini Prisms prove and effective long-term surveying solution


After making the decision to move forward with the mini prisms, the Parks Department installed 40 of the small devices to various surfaces around the site using Berntsen’s multi-purpose adhesive, designed especially to resist cracking and embrittlement even under California’s almost constant exposure to harsh UV light.


Stanley King, a Senior Land Surveyor with the California Parks Department who oversaw the surveying process from day one, cited the RSMP15 prisms as a primary component behind what he called “phenomenal survey work” given the difficult conditions of the project.


Hearst Castle Mini Prism

Photo provided by Stanley King, Senior Land Surveyor, California Parks Department

Anticipating multiple contractors working on the site throughout the two-year duration, King said it was crucial to establish highly accurate, long-term project control so that everyone was working on the same survey datum throughout every phase of the delicate renovation.


The RSMP15 Retro Reflective Mini Prism Angle Targets provide accurate, yet unobtrusive 3-dimensional monitoring for a variety of surfaces. Built to monitor formwork during construction or renovation projects of all kinds, these are the perfect solution for bridges, railway tracks and tunnels where long distances can make accurate surveying even more difficult.


To learn more about Berntsen’s selection of Mini Prism Angle Targets or any other product we carry, contact us for more information today, or grab our product catalog.


Don't forget to check out our full line of premium survey and monitoring targets here.