Research on the evaluation of historical building values based on historic building mapping

A control survey was carried out using the Beidou system or GPS system combined with RTK [30]. For general plan mapping, digital terrain mapping or low-altitude UAV-assisted mapping is used to obtain detailed information on the current status of historical buildings and form a general building plan [31]. Single building measurement adopts the traditional measurement method, ground 3D laser scanning measurement method, close-up photogrammetry method and tilt photogrammetry method. The production of single building mapping includes the production of floor plan, elevation, section and structure details [32].

This paper attempts to realize the basic logic of “constructing a theoretical framework → mapping and survey research → application guiding practice” to carry out the value evaluation research based on the comprehensive mapping of historical buildings, and the technical roadmap of the research is shown in Figure 1.

Fig. 1

Through screening, the authors identified 20 historical buildings in Taizhou City as research subjects, which vary greatly in terms of construction age, architectural style and historical value. The purpose of this study is to evaluate the value of these 20 buildings included in the list of historic buildings to determine their level of protection and to suggest strategies for the conservation of historic buildings.

There is no unified understanding of the content of historic building archives in China yet, so we refer to the EH 2006 publication Understanding Historic Buildings: A guide to good recording practice for a grading of historic building records. The descriptive file was selected for in depth recording of historic buildings in Taizhou. Figure 2 shows the contents of the descriptive file.

Fig. 2

Descriptive archives emphasise the completeness and presentation of details of information related to the building. The field survey includes both interior and exterior surveys, collecting basic data, such as location, age, and type, in addition to more information about the building such as architects, architectural chronicles, historical photographs, and making preliminary judgements about the building’s surface materials and architectural style and form [40, 41].

Figure 3 shows the descriptive file of one of the historic buildings mapped and researched by the authors. A total of 20 historic buildings were researched in this study, and due to space constraints, the descriptive files of other buildings will not be provided in this paper.

Fig. 3

For historical buildings that have been listed for conservation, their value has been affirmed by the expert group. What needs to be considered here is whether the building value is outstanding to determine whether the building needs to be protected or repaired in a more in-depth manner. In this paper, four items, namely, historical value B1, artistic value B2, scientific value B3 and environmental conditions B4, are selected as evaluation indicators with reference to China’s Cultural Relics Protection Law. From the perspective of the building, the more dangerous the situation is, the worse the integrity and use status of the building is, the more attention and protection it needs, so the degree of threat to the building B5 is taken as an evaluation index. Based on the idea of “determining the level of archives according to actual needs” as pointed out in the British Understanding Historic Buildings: A Guide to Good Recording Practice, we chose to determine the archival needs B6 as the evaluation index, taking into account the archival needs of domestic historic buildings. Since this paper is based on the evaluation of the value of historic building, mapping B7 was chosen as an evaluation index.

The value of historic buildings is diverse, and there are different opinions on the composition of the elements of the value of historic buildings. Combining the literature and the current situation of domestic historical architecture research, this paper is based on the assumption that historical value B1 contains the following five main elements: the age of construction, the cultural relevance of architectural history, the integrity of architectural preservation, the relevance of significant historical time or celebrities and the degree of reflecting local folk traditions. Artistic value B2 includes the aesthetic value of architectural ontology art and the value of architectural details and decoration techniques. Scientific value B3 includes the scientific nature of architectural techniques, structural technical features and the level of construction technology. Environmental conditions B4 include the conditions of the location, the coordination of surrounding structures and the richness of environmental elements. The degree of threat to the building B5 includes the degree of social threat and the degree of environmental threat. Archival needs B6 include the urgency of archival collection and the value of archival research. Mapping demand B7 is mainly measured by the difficulty of mapping.

According to the above analysis, this paper constructs the index system of historical building value evaluation factors as shown in Figure 4.

Fig. 4

The evaluation of the value of historic buildings is a complex systematic evaluation, and different countries and regions have different scoring standards for the development of evaluation criteria. Some use the percentage system and some use the single-point system, but we should notice that the difference between these scoring methods is only in the final expression of the score, but the core of the substance is still the same, that is, the performance of each value factor is whether high or low. In addition, for a historical building, people have a greater perception of very good, average and poor, and these three feelings also represent the three attributes of historical buildings in terms of value points.

Therefore, in this paper, three levels are used as the grading method, with different scores ranging from 10 to 1 indicating very good, average, and poor levels. A score from 10 to 8 indicates that the historic building has outstanding characteristics in this value point, that from 7 to 4 indicates average performance in this value point, and that from 3 to 0 indicates that the value characteristics are not obvious or poor. For each value point, there is an expression corresponding to these three levels, as shown in Figure 4.

Based on the above-mentioned map of the historical building value evaluation index system, this study produces a questionnaire for experts in historical building value evaluation. We selected eight experts and distributed 20 value evaluation questionnaires of historic buildings to each expert, and a total of 160 value evaluation questionnaires of historic buildings were returned. These questionnaires provide the basic information for the subsequent evaluation of historical building value clustering analysis.

In this section, we process the data of 160 questionnaires by k-means cluster analysis. K-means is one of the basic and most widely used division methods in cluster analysis. K-means algorithm is the most common and popular algorithm using the variance criterion. K-means algorithm is described as follows: first, k objects are randomly selected each of which initially represents the mean of a cluster. For each remaining object, it is assigned to the nearest cluster based on its distance from the centre of each cluster. The mean value of each cluster is then recalculated. This process is repeated until the criterion function converges. The commonly used squared error criterion function is defined as follows: E=∑j=1k∑x∈sj‖X−mj‖ E = \sum\limits_{j = 1}^k {\sum\limits_{x \in {s_j}} {\left\| {X - {m_j}} \right\|} }

Here, E is the sum of the squared errors of all objects in the sample set, X is the point in space, denoting the given data object, m is the cluster, and s is the mean. This criterion attempts to make the generated k resultant clusters as compact and independent as possible, without further variation.

K-means clustering is suitable for large sample studies, and the sample size of 180 obtained for this survey meets the basic requirements for cluster analysis. Since there is a strong correlation between the parameters in our statistical table and the values of the variables are not different in order of magnitude, the amount of statistical data is very large, and the application of k-means clustering in SPSS can achieve scalable and efficient data classification, which divides 20 historical buildings into four categories. From the data analysis, it can be seen that different historical buildings are different in terms of historical value, scientific value, artistic value, environmental conditions, degree of threat to the building, archival needs and mapping needs. The proposed building classification method combines the influence of various factors on the evaluation of the value and protection level of historical buildings, which is different from the common traditional type classification.

The sum of historical value, scientific value, artistic value, environmental conditions, degree of threat to the building, archival demand and mapping demand of each key research building were used as variables and imported into SPSS statistical software for k-means cluster analysis. As shown in Tables 1 and 2, after the third iteration, the centre shifts of all four classes were less than the judgement criterion (0.02), and convergence was achieved because there were no changes or small changes in the cluster centres, and the cluster centres were obtained and the cluster analysis was completed.

On the basis of quantitative evaluation and cluster analysis, combined with the principles of historic building recognition and the actual situation of historic building research, we identified the first category of buildings as historic buildings, namely, the Shrine Mountain Temple and Hui Pu Lang in Jiaojiang District and the Guan Di Temple, Ren De Tang Wang House and Sheng Tang Hall in Keng Kou Village, Huangyan District, a total of 5, respectively. The second category of buildings corresponds to the traditional style and appearance buildings, namely, the Dai Tou Temple Theatre Pavilion, Cai Yu Ancient Residence, Luqiao Shiqu Erbao Fortress, Shiqu Fortress, Jiaojiang Daotou Jin Ancestral Hall, Tianshun Chang Department Store, Huangyan Happy Hall Wang Ancestral Hall, Shantou Jingtang Playhouse, Chen Yuan Sheng Department Store and Yang Ancestral Hall, a total of 10. The remaining three or four types of buildings were listed as general buildings, respectively, Luqiao District’s new volume bridge, Xiao Wang Road corridor, hit the net bridge, Jiaojiang District’s Maqi Road corridor and Huangyan District’s Guoguo Temple Playhouse, a total of 5.

Figure 5 shows the information of the first category of historic buildings obtained after the evaluation of the value of historic buildings.

Fig. 5

The first type of buildings is mainly the buildings from the Ming and Qing dynasties. These buildings have been built a long time ago and have prominent historical and cultural significance. The architectural style and quality are good. The architectural details and courtyard structures are relatively intact, and the structural decoration and sculpture are exquisite. They can profoundly reflect the local folk custom and national culture, and have high historical value, artistic value, scientific value and strong environmental conditions. In the second type of buildings, the Ming and Qing Dynasties and the Republic of China accounted for half, respectively. Although this type of buildings basically retained the traditional style, some buildings were seriously damaged due to factors such as years of disrepair, improper use and long-term vacancy. Some buildings were transformed in the late period, and the preservation was general. There was a certain gap between the historical value and the first type of buildings. The third and the fourth types of buildings are mainly from the Qing Dynasty. Although they can see the original form and have certain historical, artistic and cultural relics protection research value, they have been seriously destroyed due to natural and human factors such as long history, wind and rain, long-term disrepair, insufficient flood discharge and so on. The traditional style and features have been seriously damaged. Some of them only have some beams. There is a large gap between the historical value and the artistic value of the first and second types.