1997 Vol. 22, No. 2
Geographic information systems are very important vehicles running on Information Superhighawy and serve many different users with geo-spatial data. The two characters of GIS are technology-driven and application-oriented. With the rapid development of computer technique, communication technique, space positioning technique, remote sensing and visualization technique GIS hardware and software environment and the methods of spatial data acquisition, storage, access, analysis, representation and visualization will be improved continually and rapidly. Facing this situation the author try to think about geographic information theory. Main discussion in this paper includes:optimal representation of spatial data with attribute data in computer, automatic acquisition and updating of spatial data, spatial data quality and uncertainty, spatial query and analysis of GIS data, visualization symbolization and multi-scaling representation of spatial data etc. On the discussion we pay more attentions to compare and to distinguish the differences between computer based GIS and paper map based "analogue GIS" and to consider the developing tendency of tomorrow's computer technique and information science.
According to definition of geo-data model, it has been analyzed that time is a basic property of geographic entity and how to study geographic time in GIS. In the case of reality geographical environment changing fastly and application focusing on analysis of local change, current geo-data model have many flaws such as redundant storage of unchanged data、difficult extraction of temporal information、implicit representation of temporal property of geographic entity. Based on the law of existing many synchronous changing small units, a temporal geo-data model with timestamp on the group of synchronous changing data items and the segmented topological arc is presented, which reduces redundant storage and shows us apparent temporal property of geographic entity.
Octree is one of the most studied and used raster structures in 3-D GIS. In this paper, linear octree encoding method is introduced firstly, three-dimensional run-encoding is then developed to compress octree data. Finally some tests are made to confirm the results.
Query languages are the most sensitive functions to users. Spatial database query languages should completely supply users with needed data which describe some spatial phenomena. This papaer will give a brief description of the current situation on the spatial database query languages and their main forms. Through analysis of the requirements for spatial database query languages, we boil down, based on characteristics of spatial data and general requirements of query languages, that the query languages must be equipped with the three features:understanding "spatial concepts", descriptive representation of queried results and declarative query process. In the final part of this paper, we outline the main features of three main aspects in spatial database query languages and the key research topics on the query languages in the future.
The translational free oscillations of the Earth's innen core, which are often called Slichter modes, are studied. The periods of them are computed by solving the governing ordinary differential equations singular at the Earth center using the Chebyshev collocation method. The results are in accordance with that of many other authors[7,8].The main difficulties of the problem are risen by the singularity of the equations at the Earth center. If some usual numarical methods are used, the equations must be treatedspecially at the Earth center. As this problem contains an infinite number of equations which are coupled one another, truncation must be made in practical solution. The necessity of special treatment at the Earth center hinders to truncate at higher order and hence limits the accuracy of the result. The Chebyshev Collocation method proposed in this paper is able to overcome the difficuties of the singularity without further special development. Hence one can truncate at as higher order as one want as far as his computing device permits. In this paper, the author has chosen to solve a system of 16 ordinary differential equation. This corresponds to a truncation of order 4 in the inner core and mantle and of order 8 in the outer core. Within the knowledge of the author, this level of truncation has never been achieved before.
In this paper, the range of the redundant observation component for correlated and uncorrelated observations is discussed, and the difference between the redundant observation component and the internal reliability is proved. Then, the further study on using the problem of reliability indicators is taken, and when one multiple correlation coefficient is different from another for correlated observations. Their internal and external reliability indicators should be simultaneously considered. Finally, an actual example of GPS stop and go positioning is analyzed.
In geodesy many models are nonlinear models. The classical method dealing with these nonlinear models is linear approximation using the approximate value of parameter. Due to the difference of nonlinearity between different nonliear models, some nonlinear models can be linear approximation and the others can be not. How to measure nonlinearity of nonlinear models? This paper introduces a method to measure nonlinearity of nonlinear mdoel and presents a numerical standard for linear approximation-acceptable curvature.
The crustal deformation induced by groundwater drainage is a sort of important atectonic deformation, by which there is significance in studying dynamic geodetic surveying in high precision, tectonic deformation and variation of station coordinates in the Coventional Terrestrial Reference System with millimeter precision. It is very hard, however, to calculate accurately the deformation due to groundwater drainage. Based on Segall's work the authors have derived the integral analytic expressions with groundwater drawdown, for surface vertical and horizontal displacement due to a well withdrawal of groundwater permeable flow in radial direction. And the authors make use of these expressions to compute quantitative displacement caused by a single well drainage in steady and non-steady groundwater flow in several canonical strata. According to the researches mentioned above, drainage wells are all complete penetrating ones, and incomplete wells are not discusssed. As we all know, permeable features of confined unfull penetrating wells are different from those of confined full wells. The confined unfull well is about three-dimensional flow, but the latter is about two dimensional flow. It is the three-dimensional flow that makes us meet more complex problems when computing crustal deformation caused by the drainage of groundwater for an unfull well. With some hypothese, the authors have made quantitative calculation of crustal deformation induced by the drainage of an incomplete penetrating well in confined aquifers without complement of leakage water. The corresponding formula has been given and the concrete schemes have been also discussed. At last the numerical integration programs have been made in line with Hermite integral formula with 20 nodal points. The examples, of course, in this paper show that the way explained here is effective.
By combining with map digitization for GIS spatial data capture and LSA (Least Square Adjustment), the authors established the collation models and accuracy eveluation criteria for line rectangle features. The analysis results were also presented in the paper. The technical procedure adopted can also be used to realize efficient quality control of captured data in GIS spatial database.
The formulas of error propagation for nonliner model are given and improved in order to be simplified and be really used in practice, and its application in error analysis and procession of spatical data of GIS are discussed. This paper studies its importance and use fulness for spatial data of GIS and draws a conclusion that nonlinear error propagation really describles accuracy.
On the basis of the mathematical expressions of the cartographic contents and mode, the mathematical definitions of maps are studied. By conducting the implicit map and transformation condition in the map definition all sorts of the cartographic information belong to map category, and thus the map definition gets a more general and precise expression.
Labels are an important ingredient in map. Whether labels are in place or not it plays an important role on the readability and usefulness of a map. However, in computer cartography, it is common knowledge that the labeling effect and speed are not ideal yet. Today, even though some other areas of computer cartography have been greatly improved, the automatic label placement is still a great problem. So more researches should be put into label placement. But recent mathematical analysis of cartographic label placement task has shown that finding optimal labeling is prohibitive due to the inherent computational complexity of the problem. This result implies that seeking an efficient algorithm for optimal label placement is a hopeless task. What we can do is to find near-optimal labelings in a reasonable time. This paper provides an optimal labeling algorithm based on backtracking,the algorithm has been put into practice and gotten better effect than some other optimal labeling algorithms.
Nowadays the rise of Desk Top Publishing system and electronic map is an important representation of modern cartography technology.The electronic environment provides cartographers with powerful tools,such as color adjustment,graph layer intergration,sheet layout,dynamic symbol generlization and statistic chart automation.The paper illustrates the DTP mapping system component and its characteristics,also discusses the change in map design compared with traditional manual design techniques.In the latter,the paper investigates the properties of new kind of map——electronic map or atlas,which involves dynamic,interaction and hypermedia structure.Some special principles for electronic map design are presented in the end of paper:extending visual variable of map symbol,multiple sheet single tack map replacing single sheet multiple task map and leading map users participating in map design during the process of implementing map.
For zooming in or out the map in a real time GIS application,and for quick transportation of the vector map in a network,this paper proposes the on-line map generalization concept.It discusses the on-line simplification to the line object in detail.Two algorithms are proposed.Their Complex are all from θ (1) to θ(n).It is a great progress comparing the normal DP algorithm whose complex is from θ(n) to θ(n2).The discussion about the reducing the spatial complex is also involved in the paper.
Determination of the color display gamuts is the presupposition to convert color space in color management system.The triangular region produced by plotting the CIE1931 chromaticity coordinates of the red,green and blue display primaries and connecting them with straight line is often referred to as the color display gamut,which is not enough to describe generally the color display gamuts at all luminace.Because,the shape and size of color gamuts will change if the color luminance change.In this paper,the authors provide instruction on determining color display gamuts at all luminance.
In this paper,the quality of cycle error and error for unshapely phase with photo-electric ranger are discussed.The impacts of aforesaid errors on measurement are analyzed.The experimental results are also given.Then the suggestion about the improving the testing of error is given.
Automatic synthesize is an important work in design of complicated combinational logic circuits.Based on improving Q-M method,a new method is proposed in this paper by using strategy of advance probe.The efficiency of computation is improved.
Based on having analyzed the working principle of the laser-typersetter,this paper describes a design of the control interface between a computer and a laser-typersetter.Some problems,such as the speed matches,the storage of graphical data, are discussed in detail.In the control process,the graphical data are stored in the high memory.To solve the speed difference between a computer and a laser-typersetter,the multi-buffering technique is used in the design.By using these methods,the whole graphical data can be delivered continuously.The basic ideal and implementing methods for data buffering,data delivering,data separating and data transforming are also discussed in this paper.
This paper introduces a depth position system for oil-well logging based on industrial computer and details the principle of hoop-joining survey,hoop-joining survey sensor,the system's composition,and its specific hardware circuit and work principle.
Elabo rated a principle of automatic measurement on noncontact thickness using laser and image sensor. Experimental results show that this method is better in following the track of time and in repeating pricision measurement.
In this paper, the shear behaviour of steel fibre reinforced concrete (SFRC) composite beams subjected to uniformly distributed load is analyzed, and the form ulas for calculating the shear capacity of SFRC composite beams is proposed by testing 11 members. The test results show that adding steel fibre improves the shear behaviour of composite beams.
Based on the relationship between the wind pressure spectrum and the wind speed spectrum,the pulsating wind load in random of the aqueduct across the Yellow River was simulated with a series of cosine functions by the decomposition of cross-spectral density matrix.
In this paper,the basic theory of precision estimation about lateral piercing errors in the GPS network of railway tunnel has been discussed. According to the theory, the software for computation has been made and tested with data.Combined with the piercing errors for different lengths of tunnel GPS network has been analysed.In the end,a few basic rules about the consfraction of the GPS network in the railway tunnel and some methods for rough estimation in lateral piercing errors is GPS network of railway tunnel have been proposed.