Trig Point Camera Mount

One feature common to all UK landscapes is a trigonometrical point, more commonly known as a trig point. These were used for land surveying and mapping prior to the advent of GPS and conjure up images of lots of polished brass instruments in varnished wooden boxes being lugged up mountain sides. The trig point network is now over 80 years old and it should come as no surprise to know that there’s a comprehensive and informative website dedicated to the subject.

Because each trig point has a direct line of sight to at least two others then they’re usually located at spots with pretty good views. I had an idea for a photo project which was to take some 360° images from each local trig point, annotate them on a web based map and provide a viewer that would allow the user to navigate around the image ( similar to  GigaPan images ).

Design

Needless to say there were a few problems. The main issue is that the top of a trig point is not big enough to put a tripod on so that the camera can be rotated through 360°. Having made the 3D printed ‘L’ bracket I thought that it should be fairly easy to design and print a suitable mount. Initially I wondered about making something that screwed into the centre section of the trig point ( see left ) with a rotating bracket on top. However while walking on the Gower Peninsula with my friend Richard we found a trig point where somebody had filled the centre section with concrete so my threaded insert idea was a non starter 😦

The second idea was to use the three brass grooves on the top of the trig point to locate a flat plate that could then hold the rotating bracket. I suspect that this was the original function of the brass grooves anyway. After making a few measurements I knocked up a plywood prototype, together with some bolts ground to a point to sit in the grooves. This worked fine ( see right ) so I proceeded on to designing the actual item.

Printing

The final design ended up in four parts, mainly to make the 3D printing a bit easier. The following are two screen captures from Meshlab showing how the parts interconnect with some more detailed descriptions below:

Bracket

This is a modified version of the previous ‘L’ bracket with the tripod dovetail fitting removed and an additional hole down the middle to bolt everything together. The bolt head is recessed into the top of the bracket.

Top plate

This allows the bracket to rotate on the base. Ideally it would have been printed as part of the bracket but that would have made the 3D print a little more tricky with more supports needed. I was also slightly concerned about clearances and tolerances so it was easier to make this part separate in case a re-print was necessary. During final assembly I glued this part to the bracket using the bolt to align the two.

Base

The base has three main functions:

  1. Support the bracket and allow it to rotate
  2. Fit into the grooves on a trig point and allow the base to be levelled using 3 adjustment screws.
  3. Indicator marks every 10° to allow the camera to be rotated evenly.

Bottom plate

I wasn’t sure whether this was necessary and my original idea was just to drop the bracket/top plate into the base. However I figured that a plate underneath would lock it in place more securely.

Extra parts

I used a few extra parts:

  1. M5 bolt and nyloc nut to hold the bracket, top plate and bottom plate together.
  2. 3 x M5 captive nuts in the recesses under the base for the adjustment screws
  3. 3 x M5 bolts ground to a point to sit in the trig point grooves and acted as height adjusters

Some comments after assembling:

  1. I was concerned about the tolerances where the various parts fitted together. For the holes that were to take bolts then I made them slightly undersized and drilled them out to the right size.
  2. I was also concerned about the recesses for the captive nuts. My original intention was to glue these in place so I sized the recesses accordingly. However I found that I hadn’t allowed enough quite tolerance so the nuts were just too large to fit. Before I resorted to grinding the nuts down I tried tapping one into the base with a hammer and I found that it was a perfect push fit with no glueing needed. A lucky escape there 🙂
  3. Although I added indicator marks on the base I didn’t add a corresponding mark on the top plate to show the current rotation. This was easily fixed with some sticky tape and marker pen.

Testing

Once everything assembled OK then it was time to try it for real. So I went off to the nearest trig point and created a panorama. To my slight surprise everything worked perfectly:

The final output after stitching the 36 images together using Hugin looks something like this:

This is obviously scaled down and the original image was roughly 27000 x 3000 pixels and the TIF output from Hugin weighed in at about 258 Mbytes. In theory the maximum height could be nearer 4000 pixels but it’s pretty much the same as I’m getting from the tripod mounted ‘L’ bracket so I’m happy with it.

Obviously this is not the best way to display a panoramic image so the next step is to find a suitable online viewer.

 

 

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3 Responses to Trig Point Camera Mount

  1. Richard says:

    Nice work! I think Pannellum is the way to go for the web view, possibly via an iframe. Looks like the occasionally concreted in threaded insert defined the centre from that OS quote, although your three-point setting should find the same centre well enough.

    Only 5500 pictures to go 😉

    Liked by 1 person

    • Yes, I’ve got a couple of upcoming posts on Pannellum. Watch this space as they say. I’ve found another one with a concreted centre, it seems to be more common for the more accessible / popular trig points. I’ve never seen one with the original cap screwed in ( they’ve probably all been nicked ).

      > Only 5500 pictures to go
      🙂 I like a challenge

      Like

  2. Pingback: Pannellum – Panorama Viewer | The Retired Engineer

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