From consistency to flexibility: Handling spatial information schema thanks to a middleware in a 3D city modeling context

Twinning elements of reality gains a growing interest in support of decision-making, learning, and simulations: a single and shared model should provide a unique integrative basis for managing assets of any replica of the real world. From a technical viewpoint, sharing and opening information requires both an exchange format and a high degree of freedom and flexibility. It should allow an important number of users to manage this information, to modify it, etc. Storing and manipulating spatial information concerning the urban built context currently focuses on ensuring consistency thanks to relational databases and predefined schemas. Following a paradigm shift from a relational database to a NoSQL database, a schema validation middleware is proposed to improve the flexibility of storage by conceding a share of its consistency. The flexibility improvements thus provide users a common basis that is able to evolve all along the lifecycle of their models and applications as required for twinning things. It allows users and their applications to take advantage of new storage features such as common: versioning, partitioning, prioritization, applications profiles, etc. The middleware and their new capabilities are illustrated thanks to the CityJSON encoding and its simplified schema for a document-oriented database.     

The solution of linear inverse problems in satellite geodesy by means of spherical spline approximation

In this paper we consider a certain class of geodetic linear inverse problems in a reproducing kernel Hilbert space setting to obtain a bounded inverse operator . For a numerical realization we assume to be given at a finite number of discrete points to which we employ a spherical spline interpolation method adapted to the Hilbert spaces. By applying to the obtained spline interpolant we get an approximation of the solution . Finally our main task is to show some properties of the approximated solution and to prove convergence results if the data set increases. Received 4 October 1995; Accepted 8 July 1996     

Visualizing Migration Flows Using Kriskograms

This paper describes a new approach called kriskogram to visualizing migration flows. To create a kriskogram, geographical units are projected as a set of points on a straight line segment called a location line. The migration flow between two points on the location line is represented using a half-circle drawn from the origin to the destination in a clockwise direction. Translucent symbols and a classification scheme can be used to make a kriskogram more effective. We demonstrate this method using a set of interstate migration data of four time periods for the conterminous United States.     

Reference frame stability and nonlinear distortion in minimum-constrained network adjustment

The aim of this paper is to investigate the influence of the minimum constraints (MCs) on the reference frame parameters in a free-net solution. The non-estimable part of these parameters (which is not reduced by the available data) is analysed in terms of its stability under a numerical perturbation of the constrained datum functionals. In practice, such a perturbation can be ascribed either to hidden errors in the known coordinates/velocities that participate in the MCs or to a simple change of their a priori values due to a datum switch on a different fiducial dataset. In addition, a perturbation of this type may cause a nonlinear variation to the estimable part of the reference frame parameters, since it theoretically affects the adjusted observations that are implied by the network’s nonlinear observational model. The aforementioned effects have an impact on the quality of a terrestrial reference frame (TRF) that is established via a minimum-constrained adjustment, and our study shows that they are both controlled through a characteristic matrix which is inherently linked to the MC system (the so-called TRF stability matrix). The structure of this matrix depends on the network’s spatial configuration and the ‘geometry’ of the datum constraints, while its main role is the filtering of any MC-related errors into the least-squares adjustment results. A number of examples with different types of geodetic networks are also presented to demonstrate the theoretical findings of our study.     

Refinement of the short arc satellite altimetry adjustment model

The short arc adjustment mode makes a determination of the geoid surface possible without the requirement of highly precise reference orbits. In this mode, the state vector components are subject to adjustment and represent in fact a set of independent weighted parameters. In a most elementary approach, the radial distance to a satellite point is differentiated with respect to these parameters and a radial distance to the geoid (r) is differentiated with respect to the earth potential coefficients. The observed satellite altimetry value (H) is approximately equal to the difference between these two radial distances. In the present study, a correction is introduced that makes it possible to express the mathematical model for H as accurately as practicable, good to a few centimeters. With regard to the partial differentiation, it is argued that r, in addition to being differentiated with respect to the potential coefficients, has to be differentiated also with respect to the state vector components. This gives rise to a second type of correction. It is shown that for most practical purposes, the ellipsoidal approximation to the geoid used to compute the above two kinds of corrections is satisfactory. The final results indicate that actual computation of these corrections is a very simple matter; an eventual upgrading of satellite altimetry computer programs can thus be accomplished with almost no additional effort. A practical benefit of the presented analysis is faster convergence in the adjustment which, in some cases, may remove the need for iterated solutions altogether.     

大区域数字图像的镶嵌设计与方法

本文详细论述了大区域遥感图像的数字镶嵌设计思想,提出了分区加大重叠的镶嵌方法,并 讨论了色调与反差匹配、几何配准和选择最佳匹配区域等问题。为了完善计算机图像镶嵌技术, 本文还提出了消除镶嵌接缝的加权平均调整灰度的方法。     

Convex optimization under inequality constraints in rank-deficient systems

Many geodetic applications require the minimization of a convex objective function subject to some linear equality and/or inequality constraints. If a system is singular (e.g., a geodetic network without a defined datum) this results in a manifold of solutions. Most state-of-the-art algorithms for inequality constrained optimization (e.g., the Active-Set-Method or primal-dual Interior-Point-Methods) are either not able to deal with a rank-deficient objective function or yield only one of an infinite number of particular solutions. In this contribution, we develop a framework for the rigorous computation of a general solution of a rank-deficient problem with inequality constraints. We aim for the computation of a unique particular solution which fulfills predefined optimality criteria as well as for an adequate representation of the homogeneous solution including the constraints. Our theoretical findings are applied in a case study to determine optimal repetition numbers for a geodetic network to demonstrate the potential of the proposed framework.     

Corridor location: the multi-gateway shortest path model

The problem of corridor location can be found in a number of fields including power transmission, highways, and pipelines. It involves the placement of a corridor or rights-of-way that traverses a landscape starting at an origin and ending at a destination. Since most systems are subject to environmental review, it is important to generate competitive, but different alternatives. This paper addresses the problem of generating efficient, spatially different alternatives to the corridor location problem. We discuss the weaknesses in current models and propose a new approach which is designed to overcome many of these problems. We present an application of this model to a real landscape and compare the results to past work. Overall, the new model called the multi-gateway shortest path problem can generate a wide variety of efficient alignments, which eclipse what could be generated by past work.     

Shallow Landslide Susceptibility Mapping Using Stereo Air Photos and Thematic Maps

Overlay (or heuristic) models have been shown to be a reasonable method to generate landslide susceptibility maps. However, overlay models are subjective and rely on expert judgment. The method developed here employs an overlay model but it tries to estimate certain parameters, such as slope angle or distance to streams, in a more quantitative manner. Each individual factor believed to have an influence on mass wasting processes is scaled to a value between 0 and 1. All different factors are then multiplied, producing the degree of stability, D_f, which lies on a ratio scale, rather than a nominal or interval scale. Thus, a pseudo probability of failure can be obtained. The data required are derived partly from thematic maps and partly from stereo air photos. The air photo stereo pair is used to automatically derive a digital elevation model which is then used to create an orthoimage of an area. The air photos are also used to develop a land use map, an important component in estimating landslide susceptibility. This methodology was tested on a section of the Santa Monica Mountains near Malibu, California. The resulting map both visually and statistically appears to successfully identify problematic areas. Although the methodology was primarily developed to identify shallow slides, the crest of a large, deep-seated landslide was also recognized. The general methodology should be easily adaptable to other regions or could be applied with a different set of factors than those considered in this specific case.     

SURVEYING ON LAKE RUDOLF

Abstract

The “Cambridge Expedition to the East African Lakes” reached the shores of Lake Rudolf in March 1931, and spent two months making a survey in several branches of science. The main object was biological—that is, the collection of land and water fauna and flora; but to create a background for this study the personnel of the expedition was made up of a chemist, zoologist, geologist, and geographer. In setting about work of this sort in a region practically unknown and scientifically unexplored the first necessity is a map of the part to be worked. Collections cannot be made at random from any part of the shore-line; one region must be chosen as exemplifying one type, and that region must be worked in detail. Positions of the collecting grounds have to be marked on a largescale map, so that the correlation of types can be worked systematically from end to end of the chosen area. Water-soundings are a necessary preliminary to the study of aquatic contents, and these can only be inserted correctly on a new and detailed map; in this part of the world the shore-line changes are very rapid, being due partly to the effect of a persistently large swell (raised by the southeast trades) on a sandy shore and partly to the lowering of the water-level by intense evaporation.     

国土资源“一张图”工程建设研究

随着国土二调、地籍调查、土地利用变更调查等任务开展,完成了多个基础地理数据和业务数据库的建设,但由于各种原因,多个部门多种地图形成的“多张图”,相对独立,不能实现统一管理,因此,数据的利用程度也不高,国土资源的全程展示难以实现,且数据本身还存在一些问题,还需要对数据进行一次大整理,国土资源“一张图”工程就是要通过数据的整理和转换,解决上述问题,让数据能够统一管理、充分利用。本文讲述了国土资源“一张图”的建设目标、建设内容,并将涉及到的数据、数据库管理系统及能够提供的服务进行了详细的阐述,为“一张图”工程的建设提供参考。     

Extracting polygonal building footprints from digital surface models: A fully-automatic global optimization framework

This paper presents a fully automatic framework to extract building footprints from a Digital Surface Model (DSM). The proposed approach may be decomposed in two steps, each of them relying on a global optimization solver. The first step aims to extract rectangular building footprints directly from the DSM using a Marked Point Process (MPP) of rectangles. We introduce an energy that prevents overlapping rectangles and aligns rectangle edges with DSM discontinuities. This energy is then embedded in a RJMCMC sampler coupled with a simulated annealing to find its global optimum. Then, the second step of our framework refines these extracted rectangles into polygonal building footprints. We first create an arrangement of line segments supporting the rectangle edges. The dual graph of this arrangement is then considered in a maximum flow optimization scheme to remove edges in the arrangement which do not correspond to building edges in the DSM. Finally, 3D results illustrate a fully automatic process to build a 3D city model from a DSM only.     

Online monitoring of local taxi travel momentum and congestion effects using projections of taxi GPS-based vector fields

Ubiquitous taxi trajectory data has made it possible to apply it to different types of travel analysis. Of interest is the need to allow someone to monitor travel momentum and associated congestion in any location in space in real time. However, despite an abundant literature in taxi data visualization and its applicability to travel analysis, no easy method exists. To measure taxi travel momentum at a location, current methods require filtering taxi trajectories that stop at a location at a particular time range, which is computationally expensive. We propose an alternative, computationally cheaper way based on preprocessing vector fields from the trajectories. Algorithms are formalized for generating vector kernel density to estimate a travel-model-free vector field-based representation of travel momentum in an urban space. The algorithms are shared online as an open source GIS 3D extension called VectorKD. Using 17 million daily taxi GPS points within Beijing over a 4-day period, we demonstrate how to generate in real time a series of projections from a continuously updated vector field of taxi travel momentum to query a point of interest anywhere in a city, such as the CBD or the airport. This method allows a policy-maker to automatically identify temporal net influxes of travel demand to a location. The proposed methodology is shown to be over twenty times faster than a conventional selection query of trajectories. We also demonstrate, using taxi data entering the Beijing Capital International Airport and the CBD, how we can quantify in nearly real time the occurrence and magnitude of inbound or outbound queueing and congestion periods due to taxis cruising or waiting for passengers, all without having to fit any mathematical queueing model to the data.     

Subjectively Weighted Development Scenarios for Urban Allocation: A Case Study of South East Queensland

This article presents a GIS‐based methodology to integrate a measure of geographic attractiveness of localities in the process of allocating potential dwellings in the context of a large urban region. The methodology was developed for a study area in Brisbane‐South East Queensland (SEQ), known as the Sunbelt Region, a rapidly growing region and a popular tourist destination in Australia. In this article, we have used a multivariate technique to develop a set of parameterised linear equations to define underlying dimensions that drive residential location decision choices. Aesthetic and accessibility factors were identified in the factor analysis from data collected via a survey of Quality of Life. Spatial measures were based on a combination of network distance and kernel density estimation to calculate ‘aesthetic’ and ‘accessibility’ scenarios, which were then overlaid and multiplied by their subjective weights to create an ‘overall attractiveness scenario’. These development scenarios were integrated as a set of criteria to control the allocation of potential dwelling capacity over the next 25 years at a grid cell level.     

Measuring tree stem diameters using intensity profiles from ground-based scanning lidar from a fixed viewpoint

This paper presents a method for using the intensity of returns from a scanning light detection and ranging (lidar) system from a single viewing point to identify the location and measure the diameter of tree stems within a forest. Such instruments are being used for rapid forest inventory and to provide consistent supporting information for airborne lidars. The intensity transect across a tree stem is found to be consistent with a simple model parameterised by the range and diameter of the trunk. The stem diameter is calculated by fitting the model to transect data. The angular span of the stem can also be estimated by using a simple threshold where intensity values are tested against the expected intensity for a stem of given diameter. This is useful when data are insufficient to fit the model or the stem is partially obscured. The process of identifying tree positions and trunk diameters is fully automated and is shown to be successful in identifying a high proportion of trees, including some that are partially obscured from view. The range and bearing to trees are in excellent agreement with field data. Trunk angular span and diameter estimations are well correlated with field measurements at the plot scale. The accuracy of diameter estimation is found to decrease with range from the scanning position and is also reduced for stems subtending small angles (less than twice the scanning resolution) to the instrument. A method for adjusting survey results to compensate for trees missed due to obscuration from the scanning point and the use of angle count methods is found to improve basal area estimates and achieve agreement within 4% of field measurements.     

The truth about Ground Truth

This paper presents a critical appreciation of the book edited by Pickles called Ground Truth . It offers a response in defence of GIS, written from the perspective of a quantitative geographer's unavoidably academic view of the strengths and weaknesses of GIS and Ground Truth. In essence, there is a growing need for a multi-partisan approach to improving rather than rubbishing a geoinformation technology that is an expanding global industry of considerable relevance both to the present and to the future.     

ROAD-SURVEYING IN THE EAST

Abstract

The title of this article is wide and generous, covering the art of road-surveying under every condition of climate from snow to tropical heat and in all types of country from moist forest to arid desert, from wooded mountains to barren rocks. But there is one feature that is common to all these conditions. Skilled supervision is at a minimum, and semi-skilled subordinates do the work. This has naturally had an influence on the quality and extent of the surveying carried out as a preliminary to the making of new roads. Some junior official, frequently from a subordinate service, is detailed for a survey, and he is expected to locate the final centre-line of the road on the ground and to produce plans, sections and a complete construction estimate. How then does he set about it? He probably has a small-scale map—in India, if he is lucky, a good, contoured, one-inch-to-the-mile map; and there are almost certain to be village tracks, either cart-tracks or man-tracks. Further, there will be certain obligatory points on the route, a pass to be crossed, a river to be bridged in a particular neighbourhood where it has well-defined banks, a town or village to be served, and so on.