Pyhäjärventie 147, 07820 Lapinjärvi, Finland
The Porlom II point is located in the southern part of Finland, on top of the Tornikallio rock, Lapinjarvi. The point was established in 1833. At the summit of the Tornikallio rock, there is a dry heather heath with pines. From the top of the rock, there is a magnificent view of Pyhäjärvi. The slope of the rock is very steep. The measurement point at Porlammi is a weathered borehole in the rock. Next to the station point, there is a plaque containing information about geodetic measurements. The trail leading to the station point is very difficult. The distance between the road and the measurement point is about 500 meters, and the summit of Tornikallio is approximately 50 meters higher than the starting point of the trail. A sign containing information about the Struve measurements is located at the beginning of the trail.
The Struve Arc, once known as the "Russian" and later the "Russo-Scandinavian Meridian Arc," is one of UNESCO's World Heritage monuments. The arc consists of 265 triangulation points, along which measurements were conducted from 1816 to 1852, enabling the precise determination of the Earth's size and shape.
The reference points of this triangulation network were marked in various ways on the terrain: hollows carved into rocks, iron crosses, stone pyramids, or specially installed obelisks. Often they were marked with sandstone bricks laid at the bottom of a pit; sometimes it was a granite cube with a cavity filled with lead, placed in a pit with cobblestones.
During the project to include the Struve Arc in the UNESCO list, which lasted 8 years, special search and geodetic work was undertaken in each country to locate the original points. All information from all the Struve Arc countries was collected, structured, and standardized.
Not all of the original points were found during the special search and geodetic work carried out in recent years with active cooperation from scientists of the interested countries, and moreover, many of them were heavily damaged. Therefore, only the best-preserved points—a total of 34—were included in the World Heritage site.
Sources:
http://www.gototrip.com/publications/geodezicheskaya-duga-struve
https://www.maanmittauslaitos.fi/en/about-nls/themes/struve-geodetic-arc/information-tourists
