Construction and application research of ecological evaluation platform based on Cesium

In this study, Sentinel 2A and Landsat series remote sensing images were used to determine the weights of vegetation coverage, humidity, dryness and heat by using the principal component analysis method. The remote sensing ecological index evaluation model was used to evaluate the ecology of the Fuxian Lake area from 2013 to 2018. Environmental quality in the study area is monitored and analyzed. By developing a unified organization and management module of spatiotemporal data in the collaborative production of multi-source heterogeneous data, the mapping relationship between data and parameters is established. The 3D-web data integration decision platform is constructed. Based on the Cesium engine real-time rendering and interactive visualization network 3D platform, real-time calculation and visualization of the ecological evaluation of the Fuxian Lake area between 2013 and 2018 is realized. The ecological environment of the study area continued to deteriorate from 2013 to 2015, improved slightly in 2016, and improved significantly in 2017–2018. The platform has the functions of searching, selecting the base map, measuring on the map, and positioning the coordinates, which can achieve the real-time ecological analysis function and show the change process of the ecological environment and natural resources.


INTRODUCTION
At present, the relationship between human activities and the ecological environment is getting closer and closer. Human activities have caused profound changes and influences on the ecological environment and ecosystem, and the resulting contradictions among population, resources and environment are becoming increasingly prominent. Therefore, the study of ecological security is of great significance for understanding the status of ecological security and for making relevant ecological environment decisions. At present, China's ecological environment deterioration tendency has not been effectively controlled in general. Although there has been partial improvement in recent years, the degree of governance is still far from recovering the serious consequences caused by ecological damage. With the proposal of national ecological civilization construction, the implementation of a sustainable development strategy of harmonious coexistence between humans and nature, and the rapid development of science and technology informatization levels in recent years, society is in urgent need of the introduction of new technologies and the application of new technologies in the improvement and protection of the ecological environment (Mitrović ). The formation and development of an ecosystem will be affected by multiple factors, and a single ecological factor cannot objectively and comprehensively reflect the changes of its ecological environment (Song & Xue ). Therefore, it is particularly important to analyze the comprehensive effects of multiple ecological factors and comprehensively evaluate the regional ecological environment. In recent years, a new remote sensing ecological index (RSEI) has been proposed. It is completely based on remote sensing information, which can directly represent regional ecological quality, intuitively reflect multiple indicators of the ecological environment, and realize rapid monitoring and evaluation of the regional ecological environment, with certain practical significance and high practical reference value (Lintao et al. ). At present, the application of RSEI is mainly limited to calculating green degree, dryness degree, humidity and heat indexes respectively through the information values of different bands of remote sensing images, and then synthesizing these indexes to finally reflect the changes of ecological environment in the study area from some angles. Some scholars have used a feature inversion technology and improved remote sensing ecological index to predict the ecological change caused by population growth in the Xiongan new area (Xu et al. , ). Some scholars have made a comparative analysis of the remote sensing ecological index (RSEI) and ecological index (EI), and found that RSEI can reflect changes in ecological environment quality more effectively than EI (Shan et al. ). However, at present, most research based on RSEI can only evaluate the regional ecological quality by calculating the data of various indicators.
There is no corresponding ecological evaluation platform that has been built, and this cannot be visualized in real time.
In the digital city stage, the main task is to build a digital spatial information-sharing platform. The platform design of this stage focuses on the sharing of basic spatial data. The platform design is based on a distributed spatial database, and the data provides online services through a Web service mode. With the development of smart city construction, the space-time data integration platform based on the data center, data warehouse or virtual view gradually appears, and finally develops into a space-time data cloud platform.
However, due to the complex characteristics of space-time data, the space-time data cloud platform developed at present mainly focuses on technical implementation, while the research on the management, scheduling and visual analysis of massive space-time data is still in its initial stage. Cesium is a Javascript library that can display a 3D Earth and map across platforms and browsers. It supports 2D, 2.5D and 3D

CONSTRUCTION OF ECOLOGICAL EVALUATION PLATFORM BASED ON CESIUM Overall design
In order to realize the real-time extraction, query and analysis of ecological information, as well as the integration and decision analysis of massive real-time monitoring data, the holographic transformation of the ecosystem from static to dynamic is realized. In this study, a real-time rendering and interactive visualization network 3D platform based on the Cesium engine was constructed to realize the dynamic visualization of heterogeneous spatiotemporal data.
Cesium supports dynamic geospatial visualization and has very high performance and precision. In view of this, this study chose Cesium as the basic engine of the network 3D data integration platform. The overall design of this module is shown in Figure 1 Earth, without any plug-ins, provides a new big data visualization, real-time streaming data visualization function, through the platform can be realized fast on the browser and the mobile terminal is beautiful, smooth map plotting and spatial analysis. The core content of the platform construction is to build a Cesium-based network 3D data integration decisionmaking platform. Firstly, a unified organization and management module of space-time data is developed in the collaborative production of multi-source heterogeneous data to realize preliminary data integration. In the target matching module, the network structure and parameters of the SOM neural network are determined, and the mapping relationship between data and parameters is established to facilitate the continuous matching and fusion of data. Finally, in the data fusion module, a convenient interface for data editing is provided to realize efficient dynamic visualization and decision analysis.

Ecological evaluation decision function
The Fuxian Lake, ranging from 24 21 0 26″N to 24 38 0 06″N and 102 49 0 10″E to 102 57 0 26″E, is located in Yuxi city, the central area of the Yunnan Province. It is the largest deep-water freshwater lake in China and the largest lake at the source of the Pearl River, which is related to the Nanpan-

ings. The specific calculation formula is shown in Equation
(2). In this study, NDVIveg ¼ 0.70 and NDVIsoil ¼ 0.00, and when NDVI of a pixel is greater than 0.70, the value of Fv is 1. When NDVI of a pixel is less than 0.00, the value of Fv is 0. Therefore, the vegetation coverage was used to replace the green index in this study.   Taking remote sensing data in 2013 as an example, the humidity index diagram is shown in Figure 4(b). The index of dryness is generally represented by the bare earth SI, but in the regional environment, there are quite a number of lands for construction, and they also cause the surface of the earth to be 'dry', so the dryness index can be made of a synthesis, namely the synthesis of bare soil index SI IBI Equation (4) and building index Equation (5); ρ 2 , ρ 3 , ρ 4 , ρ 8 , ρ 11 are respectively the sentinel 2A data 2, 3, 4, 8, 11 band reflectance, and the dryness index (NDSI) is as shown in Equation (6), and the higher the value, the drier it is.
Taking remote sensing data in 2013 as an example, the dryness index diagram is shown in Figure 4(c).  Figure 4(d).

APPLICATION EXAMPLE Basic function
This study encapsulates the initialization of the map and   around the residential areas was medium, and the ecological environment of very few residential areas was poor.
Since 2017, five major projects have been carried out in the Fuxian Lake Basin, including mountain forest expansion, land adjustment and water conservation, pollution control and river control, lake management and water conservation, and habitat restoration. Therefore, the results of ecological environment assessment are consistent with the actual situation, which also proves that the ecological protection and restoration project targeted at Fuxian Lake Basin is successful.

DISCUSSION AND CONCLUSION
In this study, a real-time rendering and interactive visualiza- large-scale data calculation, a unified framework of time and space of visual display and integrated service function of ecological data integration platform, which has realized the heterogeneous dynamic visualization and decision analysis of spatio-temporal data and is used to show the changes of ecological environment. However, this system can only analyze the existing data, and cannot realize the real-time monitoring function of any remote sensing data.