This issue of the Journal of Spatial Science includes papers investigating techniques that have direct application such as road median extraction, automatic rooftop extraction, transformation of historic maps into interactive web maps, assessing vacant land as a measure of urban decline, modelling forest characteristics and an interface to visualize large space-time datasets with applications in smart cities. Additionally, research is presented on more fundamental issues such as point generalisation, and receiver code biases and positioning integrity in GNSS.
Kumar, Lewis, Cahalane and Peters present the GLIMPSE system to provide a framework for storage, management, accessibility and integration of 3D LiDAR data acquired from multiple platforms. The authors detail a point cloud retrieval approach that provides spatially optimised access to point cloud data for a particular geographic area based on user specifications. With the integrated use of a geospatial database, the GLIMPSE system and point cloud retrieval approach improved the efficiency of road median extraction.
Automatic building rooftop extraction is of great importance to many applications including building reconstruction, solar energy supply, and disaster management. The study by B. Wu, S. Wu, Li, J. Wu, Huang, Chen and Yu proposes a building rooftop extraction method using DSM data generated from aerial stereo images and vegetation cover vector data. The proposed method was applied to the centre of Shanghai, China, a typical high density urban area, and experimental results show the method can successfully extract building rooftops.
An improved method for generalisation of point features with consideration of reinforcing relationships by Zhang, Yu and Chen aims to preserve global patterns of point cluster during map scaling, an important technique for clear presentation of points in multi-scale maps. Existing methods tend to include single point features ignoring spatial interactions between different types of points, such as different types of facilities that are usually co-located together to reinforce their functions in business. In this respect, generalization of point features should consider not only their own importance but also the reinforcing effects from other nearby features.
In the article by Horbiński and Lorek a method for creating an interactive web map of the preindustrial state on the basis of analogue nineteenth-century maps of southern Poland is presented. The main objective is to present a universal scheme that allows transformation of old topographic maps into interactive web maps. The Leaflet library was used as a working environment for programming.
Receiver code biases (RCBs) have long been identified as time-constant. However, RCBs can exhibit remarkable intraday variability, that affects GNSS-based ionospheric retrieval and timing applications with different combinations. Ke, Sheng and Wang propose a modified geometry-free GNSS model to extract receiver code bias variations (RCBVs). The experiment collected data at 153 stations to test the MGF model and characterize the estimated RCBVs showing that RCBVs bear a strong linear correlation with intraday temperature, which is receiver and constellation dependent.
Positioning integrity is essential in navigation. A novel approach is proposed by El-Mowafy, Xu and Hsu that combines Advanced Receiver Autonomous Integrity Monitoring with Non-Line-of-Sight detection method using 3D city models to aid multi-constellation GNSS positioning in challenging urban scenarios. A demonstration of the proposed approach is performed with real data in an urban area in Hong Kong.
Analysis of the differences between EOP 08C04 and EOP 14C04 related to Earth rotation characteristics is performed by Sun, Xu, Zhou, N, Jiang, C. Jiang and Yang. To assess the improvement of EOP 14C04, the differences between EOP 14C04 and EOP 08C04 are firstly analysed, then the causes of the differences between the two solutions are examined. Finally, the differences are further assessed for their prediction performance using the LS+AR model.
Newman, Y. Kim, G. Kim, Lee, Gu, Forghanparast and Goldberg create and apply a Python script for longitudinally measuring the duration of vacant land uses. Populating and depopulating cities have some degree of underutilised land. The duration of vacancy, or length of time a property remains unused, more strongly influences urban decline than the amount of vacant land. Assessment of the duration of vacancy is seldom conducted, due to a lack of linking longitudinal data. This research creates and applies a Python script to track the duration of vacancy in Minneapolis, USA, to create a tool that can be utilised by cities with vacant land inventories.
Accurate spatial modelling of forest characteristics is an important challenge in remote sensing applications. Estimation of coppice forest characteristics using spatial and non-spatial models and Landsat data is undertaken by Izadi, Sohrabi and Khaledi. The authors compare the ability of multiple linear regression, geographically weighted regression, and random forest to estimate different forest attributes based on field sample data and Landsat 8 image.
This paper by Benita, Perhac, Tunçer, Burkhard and Schubiger introduces Singapore Views as a novel 3D-4D interface to visualize large space-time datasets with applications in smart cities. The engine enables a combination of GIS, geo-located data with high-resolution 3D models and multimedia. Space-time datasets from Singapore’s National Science Experiment 2016 are used to test the functionality of Singapore Views.