Digital Toolkit to Assist the Interpretation of Traditional Masonry Construction

Figures & data

Table 1. Interpretative elements aiding the identification of change in masonry (UK ICOMOS 1990, 73).

Recognising when materials have been re-used and when possible, identifying their source. Differences in material. Breaks in masonry. Notice should be taken of the precise form of the break (ragged or straight; whether aligned with internal partitions, etc; fabric change or a blocked opening). Differences in structural techniques. There are changes over time in brickwork, construction, etc. Stylistic differences in architecture and decoration. Evidence for the demolition of part of a building. This will often be shown in a masonry building by irregularities at angles or of coursing. In all cases it may be suggested by anomalies in plan, by blocked openings that cannot otherwise be explained, or by the use of a different material in making good the area demolished.

Figure 1. Pictorial classification of common masonry styles.

Figure 2. Automated segmentation of individual stones and mortar regions in an example masonry wall. a) Segmented stones in the 3D point cloud; b) Binary orthoimage obtained after the projection of the segments on the wall plane. Note that, in this work, the metric dimension of a pixel equals 1 cm.

Figure 3. Illustration of the geometric characteristics calculated for each masonry unit.

Table 2. Stone architectural features measured automatically by the proposed tools and their value to architectural interpretation.

Stone geometric characteristics	Unit	Description/Formula	Interpretation value
Area (A)	m^2	Area of the 2D surface of the masonry unit: $\mathit{A}=n_{\mathit{pixels}}{u}_{pi\mathrm{xel}}^2$ where $n_{\mathit{pixels}}$ is the numbers of pixels that make up the masonry unit in the 2D ortho-image, and $u_{pi\mathrm{xel}}^{\hspace{0.17em}}$ is the metric dimension of each pixel, e.g. 1 cm (in which case $u_{pi\mathrm{xel}}^2$ is 1 cm^2).	Masonry units with relatively larger areas. These may be acting in a structural bonding capacity and/or may also reflect the inclusion of reused masonry components that seem out of place within the masonry substrate style in which they sit (for example sills/lintels etc).
Rectangularity (R)	Unitless [0; 1]	Fraction of the area of the masonry unit to the area of its axis-aligned bounding box in the 2D ortho-image, $\mathit{R}=\frac{{\mathit{n}}_{\mathit{pixels}}}{h_{\mathit{bb}}\times w_{\mathit{bb}}}$ where $n_{\mathit{pixels}}$ is the number of pixels that make up the masonry unit in the 2D ortho-image, and $h_{\mathit{bb}}$ and $w_{\mathit{bb}}$ are the height and width in pixels of the masonry unit’s bounding box. Note: both rectangular and square stones will have rectangularity values of 1.	R tending to 1 is indicative of a stone being ashlar, whether intentionally formerly dressed or associated with naturally bedded stone.
Circularity (C)	Unitless [0; 1]	Ratio of the Area of a masonry unit, A, to the area of a circle with the same perimeter, p, calculated as the number of pixels in the boundary of the surface of the stone.$\mathit{C}=\frac{4\mathit{\pi }\cdot \mathit{A}}{p^2}$	C tending to 1 is indicative of limited or no stone dressing. Circularity is associated with an increase likelihood of construction with field boulders or other rounded masonry materials derived from geological processes.
Elongation (E)	Unitless [0; 1]	This is calculated as the eccentricity of the ellipse that has the same normalised second central moments as the region defined by the masonry unit. The eccentricity of an ellipse is a measure of how circular it is and is calculated as: $\mathit{E}=1-\frac{c}{a}$ where c and a are the lengths of the minor and major axes, respectively, of the ellipse.	E tending to 1 is indicative of elongation. Elongation in masonry units can be a function of dressing but is commonly associated with natural cleavage in the stone bedding. In terms of construction, elongated stone can be associated with well-considered, comprehensive, strong bonding.

Figure 4. Historic ground and first floor plans of Linlithgow Palace with ‘Region of Interest’ (ROI, see Figure 6) indicated to left hand side wall highlighted in red. RCAHMS (Canmore archive) (note that Chalmer was old Scots for Chamber).

Figure 5. West Elevation of Linlithgow Palace — point cloud.

Figure 6. West Elevation to Linlithgow Palace with applied automatic masonry segmentation. The ROI highlighted in green in shown enlarged.

Figure 7. ROI divided into quadrants for purpose of analysis of aiding interpretation narrative.

Figure 8. Area of stones in cm².

Figure 9. Rectangularity of stones.

Figure 10. Circularity of stones.

Figure 11. Elongation of stones.

Table 3. Visual survey description of masonry and architectural arrangement for focussed area of investigation.

ROI	Visual Survey Description
ROI Ground Floor
West range centre — Barrel vault No. 1 (ground floor)	Coursed squared rubble at ground level. Masonry style tending towards random rubble as wall height increases. Uppermost courses returning back to more regularised coursed squared rubble. Lower RHS 4 quoins noted with distinct risbond joint to now blocked opening continuing above for approx. 1.5 m. Lower masonry sections discoloured — most likely salts. Materials: Variable reddish coloured sandstone. Salt discolouration especially pronounced to base.
West range centre — Barrel vault No. 2 (ground floor)	Coursed squared rubble at ground level. Masonry style tending towards random rubble as wall height increases. Upper section becoming increasingly formed of smaller ‘bitty’ stones. Lower masonry sections discoloured — most likely salts. Materials: Variable reddish coloured sandstone. Salt discolouration especially pronounced to base.
ROI First floor
Presence chamber (1^st floor)	Generally, coursed squared rubble. Masonry style tending towards random rubble in selected regions. Large window formed with dressed lintel and profiled and chamfered jambs (RHS). Sill also chamfered. Relieving arch above lintel not extending the full length of lintel. Voussoirs formed in squared rubble masonry — no clear springers. Sizable, blocked opening in masonry characterised by large arch (upper central region). Voussoirs formed in squared rubble masonry — no clear springers. Risbond masonry section running vertically and directly below the arch (as might be expected). Stitching across former jambs and main walling fabric limited — characterised by ‘bitty infill masonry’. Above arch voussoirs (LHS) visible masonry intervention — rebuilt in smaller stones lacking coursing.
Kings hall (First floor)	Sizable blocked opening in masonry characterised by large arch. Voussoirs formed in squared rubble masonry — no clear springers. Risbond masonry section running vertically and directly below the arch (as might be expected). Stitching across former jambs and main walling fabric limited. Large window formed with dressed lintel and profiled and chamfered jambs. Sill also chamfered. Window dressing (jambs and lintel) exhibiting mechanical damage most likely associated with iron work. Relieving arch above lintel voussoirs formed in squared rubble masonry — no clear springers.