一种符合视觉规律的,基于地图数据的虚拟地景仿真

本文分析和解决了两个关键性问题，使计算机所生成的虚拟地景符合人的“越近看得越清”视觉规律，并通过实例对该方法的实现过程给予了详细的描述。     

THE CALCULATION OF THE HEIGHT OF KILIMANJARO

Abstract

The observations to height Kilimanjaro were made from two ground stations, Domberg (5,081·6 ft.) and Lelatema (5,323.1 ft.) and from a point called Kibo near Kaiser Wilhelm Spitze which is regarded as the highest point on the crater rim. It was originally intended to include a third ground station, Kifaru, but it was discovered that the ice cap obstructed observations between this point and the top.     

HEIGHTS BY ANEROID BAROMETER

Abstract

Of all methods of surveying, the provision of heights by means of aneroid barometers probably arouses the greatest variety of emotions in the practical surveyor. Some pack a single aneroid rather shamefacedly, look at it only when in difficulties and are thankful if its reading is within 200 feet of what they expect; others with as little care, expect readings correct to the smallest division of the scale; whilst at the other end of the scale are the devotees of the aneroid who will attempt-and often succeed-in raying out gravity pipe lines in flattish country with no other instruments.     

TRIGONOMETRIC HEIGHTS AND REFRACTION

Abstract

In the past there has been considerable discussion on the above subject in this Review. There is a bibliography at the end of this article in which the full titles of previous articles are given. For brevity, reference to them in the following text is made by number only. Recently, Gulatee summarized present knowledge and asked how other Survey Departments dealt with this matter. Consequently, it was considered that it would be helpful to set out in detail the procedure adopted by the Directorate of Colonial Surveys for obtaining trigonometric heights, with particular reference to primary and seoondary chains and nets.     

LOCAL ATTRACTIONS AND THEIR INFLUENCE ON THE DETERMINATION OF HEIGHTS ABOVE MEAN SEA LEVEL

Abstract

The Mythical Spheroid.—The preceding article dealt with the fact that the spheroid of reference is a myth and that, even if it were not, we could not get hold of it at any given place. In order to apply corrections to observed quantities or, more generally, to operate upon them mathematically, we must make some assumption such as that of the spheroidal level surface. Probably a lot of harm has been done by attaching the notion of too concrete a thing to the spheroid. Disputes and misconceptions have arisen. People talk of“putting the spheroid down at a point” and imagine that the obedient thing is still at their feet when they get to another point, perhaps distant, in their system of triangulation or what not. Actually the spheroid may be disobedient not only as regards the direction of the vertical but also because it is above their heads or below their feet. What happens is that at each point afresh the computer treats the observations as if they were made there on the surface of a spheroid. In the same way, but travelling still farther along the road of hypothesis, he may treat observations for astronomical positions as if the compensation for visible elevations were uniformly distributed as a deficiency of density down to a depth of 122·2 kilometres. That was the depth which happened to give the smallest sum of squares of residuals in a certain restricted area, but nobody imagines that it corresponds with a physical reality, especially the ·2! It was a convenient mathematical instrument which, once the theory was to be given a trial, had to be fashioned out of some assumption or another. All this has little to do with geodetic levelling but is meant to try to banish the spheroid out of the reader's mind or at least to the back of his mind. In what follows we shall be compelled to make a certain amount of use of the family of spheroids but always with the above strictures in view.     

LOCAL ATTRACTIONS AND THEIR INFLUENCE ON THE DETERMINATION OF HEIGHTS ABOVE MEAN SEA LEVEL

Abstract

Preliminary Note.—The substance of this article was written in 1921 at the request of Lieut-Col. Wolff, who was then in charge of the Levelling Division of the Ordnance Survey and with whom the author collaborated in writing “The Second Geodetic Levelling of England and Wales, 1912–21” under the direction of Sir Charles Close. It was not intended for publication and was not again considered until 1928, when a discussion by correspondence was started by the Surveyor-General of Ceylon on the subject of hill circuits in levelling. In this discussion the survey authorities in Great Britain, Canada, India, and South Africa took part, but the main theme was the accumulation of error due to the large number of sightings necessary in hilly country and the question whether a common formula for such country and for flat country was justifiable. In his contribution Dr. van der Sterr made a brief allusion to the subject of the present paper and Dr. de Graaff Hunter went into details. His contribution and the following remarks therefore have some arguments in common.     

基于北京一号卫星影像的建筑阴影测量建筑高度的应用研究

在分析遥感影像建筑物阴影与实际高度关系的基础上,阐述了依据影像阴影估算城市建筑物高度的原理和方法,设计了一种基于影像建筑物阴影特征快速提取高程信息的技术方法。在使用北京一号影像数据的试验中,70%的有阴影楼房测量误差在4米以内。     

THE HEIGHT DETERMINATION OF MOUNT KILIMANJARO TANGANYIKA,EAST AFRICA

Abstract

The following account of the expedition which succeeded in fixing a new height for Mount Kilimanjaro is taken in the main from the diary of the party that made the necessary observations, but, for the sake of clarity, it is as well to set out here a very brief statement of the position.     

WAVE HEIGHTS IN THE SURF ZONE

The advantages and disadvantages of measuring ocean wave heights in the surf zone by using terrestrial photogrammetry are outlined. Difficulties arising from a lack of control points can be overcome by using the apparent horizon to provide camera orientations about two axes, provided that the apparent horizon is the sea surface and that an unconventional orientation of the camera axis system is adopted. Following practical tests and error simulation studies, height differences were determined for 12 points in the breaking wave zone off a Newcastle (New South Wales) beach. It is hoped that the method can be developed as a convenient means of collecting wave data.     

HEIGHTS FROM PARALLAX BAR AND COMPUTER

The results are given of a series of tests where a stereoscope, parallax bar, and digital computer were used to derive accurate heights of a large number of points in several models. After suitable modifications of the standard formula, the conclusion is reached that results approaching those obtained with plotting machines are possible, provided that the observer has sufficient experience of stereoscopic measurement.     

SOME FACTORS IN DETERMINING HEIGHTS FROM AIR PHOTOGRAPHS

Abstract

The graphical methods developed at the War Officeof mapping from strips of vertical photographs are generally widely known. It may be fairly said that they frequently present a reasonably economical method of mapping the planimetry of a country on medium topographical scales when there is a normal third-ordertrigonometrical control, but that so far it has not been possible to provide economically for the accurate depiction of the ground relief. The reason, for this failure is due to the fact that the control required fot contouring is about one fixed height per square inch of map, and the cost of providing this control will normally be of the same order as the cost of mapping by ground methods.     

TRIGONOMETRICAL HEIGHTS AND THE COEFFICIENT OF TERRESTRIAL REFRACTION

Abstract

Mr. A. J. Morley has contributed a series of articles in the Review (E.S.R., iv, 23, 16; iv, 25, 136 and vi, 40, 76) on the adjustment of trigonometrical levels and the evaluation of the coefficient of terrestrial refraction with a view to ascertaining how other Colonies and Dominions deal with these problems. This object is very commendable as several problems concerning both the observational and theoretical sides arise in height determinations, regarding which there is not much guidance in the usual treatises on the subject.     

CORRECTION OF PLANE-TABLE HEIGHTS FOR CURVATURE OF THE EARTH AND ATMOSPHERIC REFRACTION

Abstract

Most text-books on surveying limit their discussion of the correction of vertical angles for curvature of the earth and atmospheric refraction to the correction of angles taken with a theodolite during triangulation and omit any reference to those taken with a clinometer. This is rather illogical, as in well-observed triangulation, with all vertical angles measured in both directions, no correction for these effects is necessary, whilst in plane-tabling on small scales where sketching at considerable distances is frequently employed the application of corrections for these effects is essential.     

GPS在小区域内测定点位高程应用中的垂线偏差方法

本文讨论了在局部ＧＰＳ网中通过少量重合点，考虑区域的垂线偏差，求定其它点的正常高。     

A SEMI-GRAPHIC METHOD OF ADJUSTMENT OF HEIGHTS IN A STRIP OF AERIAL TRIANGULATION

Some methods of adjusting the vertical height errors produced in a strip of aerial triangulation are discussed and a semi-graphic method of adjustment suggested.     

AN ALGORITHM TO DETERMINE THE VOLUME OF A BODY FROM IRREGULARLY PLACED SPOT HEIGHTS

The paper describes how a computer can be programmed to form triangles from points, having x, y and z co-ordinates and selected in an arbitrary manner, to calculate the area of each triangle and to determine the volume of the prism above or below the triangle. The sum of these volumes gives the total volume of a body.