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Using the Calanais I 3D scenery in Stellarium: some experiences when ground proofing.

• Introduction
  
• Some definitions
• 3D scenery components
• Aligning the 3D scenery
• Experiences
• Evaluating the directions at Calanais I
• Literature
  
• Acknowledgments

Introduction

A 3D scenery has been made of Calanais I which can be examined in Stellarium. As with all things, developments will be made and this web page will look into some of these in due time.
The present model (V1.0, 2Feb2023) does not include the nearby (50m) outcrop Cnoc an Turso, so the incoporated Stellarium landscape (Callanish I) can only be used around the North end of the avenue for a correct skyline view. On this webpage we will investigate the inclusion of this outcrop as a DSM model: aka ground proofing. Furthermore the alignment of the terrrain including site, skyline and skyscape will be reperformed. This will also provide an idea on accuracy/precision.

The DSM of Cnoc an Turso was aquired from bluesky and they provided permission to add it in the public domain Calanais I 3D scenery.

When the testing phase has passed, it is recommended to be incorporated on the main web site.

Some definitions

• in Ponting&Pointing (1981) glaim is used for reappearing
• in Curtis&Curtis (1994) re-glaiming or re-flash is used both for reappearing and regleaming
• in Curtis (2014) re-flash is used for reappear

3D scenery components

• Terrain: 3D model of Calanais I and Cnoc an Turso
• Contours of Calanais I
  
• Skyline: Literature and software
  
• Skyscape: Stellarium
  

Terrain

The terrain consists of two parts, which are included in Stellarium:

• Calanais I: 3D laser scan
  This 3D laser scan has been produced as a cooperation between Archaeoptics and Callanish Blackhouse. Furthermore it has been incorporated in Stellarium by a team of volunteers.
  This 3D laser scan provides an accurate molel of the Calanais stones (as a standalone site)
  
• Cnoc an Turso: Photographic Digital Surface Model (DSM)
  A DSM (resolution 25cm) has been acquired from bluesky (accuracy XY: ± up to 1m RMSE; accuracy Z: ± up to 1.5m RMSE). Reijs has acquired this DMS with copyright permissions (similar to the 3D scenery in Stellarium: CC BY-NC-SA 4.0), from bluesky.
  This photographic DSM had two important functions: a) it provides a relatively higth resolution (25cm) model to a outcrop some 50m from Calanais I (a model of this outcrop is essential, as it determines part of the [southern] skyline); and b) this DSM was utliised to georeference the 3D laser scan.

Contours Calanais I stones

Numbering (Ponting&Ponting, 1981, p 80) of the Calanais I stones is here:

Numbering of the Calanais I stones from Ponting&Ponting

See the uncertainty symbol for 18A and 33A. 33A was reerected in 1982, so after the publication of above numbering picture (Curtis, 2011, p. 3)

Calanais I contour by Ponting&Ponting (1981, page 100), seen from midway Stone 8 and 19

Calanais I contour by Curtis&Curtis (1994, page 30), seen with back to Stone 8

Skyline

All the below skylines do not include the nearby (50m) outcrop Cnoc an Turso. Cnoc an Turso makes the skyline variable when walking through Calanais I. When one wants to have a proper skyline, this outcrop needs to be included in the 3D scenery.

Thom (1971, pp 69)

This skyline was calculated from OS map by Thom. It looks that the declination numbers are referring to the geocentric declination (more logical would be a topocentric declination, as a Earth reference is wanted).

Curtis&Curtis (1994, pp 31)

Horizon (Smith, 2022)

Both Horizon (using SRTM 1") and HeyWhatsThat (using SRTM 3") are not able to represent the nearby (50m) Cnoc an Turso. That is a hidden advantage in this case; as the skyline would not be correct if such nearby feature would be included in a skyline (of for instance Stellarium) for many standpoints.
My experience with HeyWhatsThat and SyntH (debugging plus comparing with several other methods) is good. Horizon also maps HeyWhatsThat's skylines, so both tools give similar results (for skylines further away than 5km) and can be trusted (but keep knowing their limitations).

Skyscape

Aligning the 3D scenery

• Intra 3D scenery alignment:
  
• Georeferencing
  This was done by including Cnoc an Turso's DSM (pers. comm., Georg Zotti, 2023)
  
• Aligning the two terrains
  The inter alignment of Calanais I and Cnoc an Turso is done by mapping the stone contours in the DSM on the stones in the 3D laser scan (pers. comm., Georg Zotti, 2023).
  
• Nearby terrain (Cnoc an Turso)
  
• Contour alignment
  
• Skyline alignment
  
• Skyscape alignment
  

Nearby terrain alignment

Ponting&Ponting

Standing midway Stone 8 and 19 an animated gif: Combination of Ponting (red contours) plus 3D laser scan (gray-ish) & DSM (green: Cnoc an Turso) and Rennie's photograph (green-ish):

The contour of Cnoc and Turso DSM (green) looks similar to the photograph (green-ish). Stone 33A is tough different in Ponting (1981), as it was only positioned correctly in 1982,

Curtis&Curtis

Standing with back to Stone 8 an animated gif: Combination of 3D laser scan (gray-ish) & DSM (green: Cnoc an Turso) and Rennie's photograph (blue-ish):

The contour of Cnoc and Turso DSM (green) is slightly different (not as far extending towards the right) than the photograph (blue-ish).
The amount of gaps between stones seen in Curtis&Curtis (1994) is similar to seen in the Stellarium 3D scenery (grey-ish) and photo (background; Rennie, 2023):

Contour alignment

Ponting&Ponting

Mapping Ponting&Ponting (1981, page 100) skyline on photograph (Rennie, 2023):

Ponting&Ponting's skyline is made from midway between Stone 8 and 19.

Curtis&Curtis

Mapping Curtis&Curtis (1994, page 30) skyline on photograph (Rennie, 2023):

Curtis&Curtis' skyline is made with one's back to Stone 8.

Skyline alignment

Here we want to verify if the 3D scenery is properly aligned with the skyline (aka Stellarium landscape). This can be done by photographs that include contours of site and skyline.

Below is an animated gif from view in Stellarium (using Horizon for the skyline [black]) and a photo ([green-ish]; from Rennie, 2023):

Looking at the skylines: the skyline ([black] Horizon as Stellarium's landscape) and a photo [green-ish] of these features: not much difference can be inferred. There could be some inaccuracy of the skyline-software and some small lens distortions.

Skyscape alignment

Photo taken on July 6^th, 2023

Photos taken on July 31^st, 2023

Some 23 relevant photos were take of the Moon in relation to a stone. The evaluation of these photos is here.

Photos taken on March 31^st, 2024

Photos taken on April 28^th, 2024

Next opportunities for photos

Depending on clouds: (mooon can be visible with naked eye when more than 1 day before/after New Moon:

• 2024, April 29 (start at 06:30 BST) and April 30 (start at 7:30 BST)
• 2024, May 24 (start at 1:30 BST), May 25 (start at 02:30 BST), May 26 (start at 03:30 BST) and May 27 (start at 4:30 BST)

Workflow for observations

• At home:
  
• Re-sync the Windows PC with a NTP server: https://www.elevenforum.com/t/sync-clock-time-with-internet-time-server-in-windows-11.1320/
  This is similar for Windows 10.
• Take a photo with the camera of the synced time on the computer (for Windows the time is on right bottom of screen: if it does not show seconds, double left click the time). Or in Stellarium: (re)start Stellarium and press F5 to show the running time, do nothing else in Stellarium.
  
• On site and one can fix the camera steady on a tripod:
  
• Put the camera on a tripod with its back to Stone 8 (using possibly earlier placed golf tees).
• If not placed earlier: Place at each leg of the tripod a golf tee (for future reference).
• Have such an exposure time (below 3sec) that the Moon is not over exposed (perhaps even slightly underexposed) and that stone contours are visible against the sky.
• Use a 'small' FOV (say some 10 stones are in view, something like below picture). If you don't have such a long lens, just do what is possible.
• Stand in front of the camera facing the Moon. See (perhaps using binoculars) when a Moon's lit area starts or stops touching a contour side of a stone (so that is four touch moments for each stone), see below:
  
  
1. Touch moment 1: right side of Moon's lit area just starts touching left side of Stone 41.
2. Touch moment 2: left side of Moon's lit area just stops touching left side of Stone 41.
3. Touch moment 3: right side of Moon's lit area just starts touching right side of Stone 41.
4. Touch moment 4: left side of Moon's lit area just stops touching right side of Stone 41.
   
• The Moon's lit area is not always a cicle, but closer to first or last quarter Moon; so use the first/last moment the Moon's lit area (can be a circle-ish shope, one of the horns or straight-ish) is seen touching the stone contour.
• At each of these touch moments, stand aside of the camera and take photo.
  
• Repeat: check if Moon is still middle-ish in camera view, stand in front camera, look (with binoculars) and wait for touching moment, step aside, take photo for as many touch moments and stones as possible. Minimum 5 stones or some 10 touch moments (touch moments 1 and 3 can be the most accurate).
• On site and making hand-held photos (as one can't fix the camera on a tripod):
• Hunker down (camera in hand) with your back to Stone 8 (at possibly earlier placed golf tees).
• Have such an exposure time (below 3sec) that the Moon is not over exposed (perhaps even slightly underexposed) and that stone contours are visible against the sky.
• Use a 'small' FOV (say some 10 stones are in view, something like below picture). If you don't have such a long lens, just do what is possible.
• See (perhaps using binoculars) when a Moon's lit area starts or stops touching a contour side of a stone (so that is four touch moments for each stone), see below:
  
  
1. Touch moment 1: right side of Moon's lit area just starts touching left side of Stone 41.
2. Touch moment 2: left side of Moon's lit area just stops touching left side of Stone 41.
3. Touch moment 3: right side of Moon's lit area just starts touching right side of Stone 41.
4. Touch moment 4: left side of Moon's lit area just stops touching right side of Stone 41.
   
• The Moon's lit area is not always a cicle, but closer to first or last quarter Moon; so use the first/last moment the Moon's lit area (can be a circle-ish shope, one of the horns or straight-ish) is seen touching the stone contour.
• At each of these touch moments, directly take a hand-held photo of the Moon.
  
• Repeat: hunker down at golf-tee (with binoculars) and wait for touching moment, directly take a hand-held photo for as many touch moments and stones as possible. Minimum 5 stones or some 10 touch moments (touch moments 1 and 3 can be the most accurate).
• When back at home:
  
• Take a photo with the camera of an again re-synced time on the computer (for Windows the time is on right bottom of screen: if it does not show seconds, double left click the time). Or in Stellarium: (re)start Stellarium and press F5 to show the running time, do nothing else in Stellarium).
• Send unedited pictures (including the original EXIF data) to the group.

Experiences

The experiences are here.

Evaluating the directions at Calanais I

See here for the likelyhood of possible alignments intra and inter Calanais I with solar/lunar events.

Literature

Curtis, Ron and Margaret R. Curtis: Callanish: Stones, Moon & sacred landscape. (1994).
Curtis, Ron: Callanish 2006. (2003).
Curtis, Margaret R.: A mini-guide to the Callanish stones. (2011)
Curtis, Margaret R. and Malcolm Maclean: Midsummer sunrise alignment and symmetrical triple stone setting. In. Margaret R. Curtis (ed): Celebrations in stone of the Sun's annual cycle at Callanish.  2014. pp. 92-102.
Curtis, Margaret R. Celebrations in stone of the Sun's annual cycle at Callanish.  2014.
Kosowsky, Michael: HeyWhatsThat. In: http://www.heywhatsthat.com/ (2012), Accessed 2 September, 2022.
Ponting, Margaret R. and Gerald Ponting: Decoding the Callanish complex: Some initial results. In: BAR British Series. 88 1981.
Smith, Andrew: Horizon. In: http://www.agksmith.net/horizon/ (2020), Accessed 10 September, 2022.
Stellarium. version: 1.2 In: http://stellarium.org/en/ 2022.
Thom, Alexander: Megalithic lunar observatories. Oxford University Press 1971.

Acknowledgments

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