45 Degrees North Latitude Point (West Side/Horonobe)

The road to OSC2023 Hokkaido(it's hard to get there). This was the main destination for Day 2 of my trip from Wakkanai to Sapporo. The 45 degrees North latitude monument in Horonobe. The "perfect diagonal" of the Earth.
The day before, I stopped by the monument in Esashi Town, which is the 45-degree point on the east side, but this is the western end.
45 degrees North latitude in Esashi: https://note.com/sakaik/n/ne6a052807d2b

Location of the 45 degrees North latitude point in Horonobe

It is located about 1.5 hours south of the Wakkanai area along Hokkaido Prefectural Road 106, the Wakkanai-Teshio Line. It is located shortly after passing through the snow shelter. The photo shows the view looking north from the 45-degree monument point.

45 degrees North latitude monument (Horonobe)

After passing through the tunnel (shelter), 45 degrees North latitude monuments greet you on both sides of the road.

On the side heading south, there is a monument made of wood angled at "45 degrees".

On the side heading north, there is a monument made of metal with the letter "N," representing North latitude, angled at 45 degrees. Visible in the distance is Rishiri Fuji. It had been watching over my path on the right side of the road for over an hour since I left Wakkanai. It is truly amazing that you can see it forever and everywhere (my vocabulary is failing me).

What is the geodetic system of the 45 degrees North latitude monument (Horonobe)?

Now, while I am moved by being at the 45 degrees North latitude point, is this really 45 degrees North latitude? Let's ask the GPS logger.

The result is 45 degrees 0.134 minutes North latitude. This also matches the 45-degree point in Esashi (the one built on the road). At a glance, the deviation is about what you would expect from the Japanese Geodetic Datum.

Let's calculate. 45°00.134′ North latitude, when converted to degrees, becomes 45.002233... degrees. Since this is the value obtained by GPS, when I convert this from the World Geodetic System to the Japanese Geodetic Datum, it becomes 44.999990497 degrees North latitude. Incidentally, 45°00.135′, which is this GPS value with the last significant digit incremented by 1, is 45.00225 degrees, and when converted to the Japanese Geodetic Datum, it becomes 45.000007200 degrees, so I found that a value corresponding to "45 degrees North latitude in the Japanese Geodetic Datum" was obtained quite accurately within the range of the GPS logger's significant digits.

By the way, 45 degrees North latitude in the Japanese Geodetic Datum is 45.0022428 degrees in the World Geodetic System.

Other photo collection

Back side of the wooden monument

Back side of the metal monument