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1.
Investigating the propagation mechanism of unmodelled systematic errors on coordinate time series estimated using least squares 总被引：6，自引：8，他引：6
The propagation of unmodelled systematic errors into coordinate time series computed using least squares is investigated,
to improve the understanding of unexplained signals and apparent noise in geodetic (especially GPS) coordinate time series.
Such coordinate time series are invariably based on a functional model linearised using only zero and first-order terms of
a (Taylor) series expansion about the approximate coordinates of the unknown point. The effect of such truncation errors is
investigated through the derivation of a generalised systematic error model for the simple case of range observations from
a single known reference point to a point which is assumed to be at rest by the least squares model but is in fact in motion.
The systematic error function for a one pseudo-satellite two-dimensional case, designed to be as simple but as analogous to
GPS positioning as possible, is quantified. It is shown that the combination of a moving reference point and unmodelled periodic
displacement at the unknown point of interest, due to ocean tide loading, for example, results in an output coordinate time
series containing many periodic terms when only zero and first-order expansion terms are used in the linearisation of the
functional model. The amplitude, phase and period of these terms is dependent on the input amplitude, the locations of the
unknown point and reference point, and the period of the reference point's motion. The dominant output signals that arise
due to truncation errors match those found in coordinate time series obtained from both simulated data and real three-dimensional
GPS data. 相似文献
2.
A method is presented for filtering and classification of terrestrial laser scanner point clouds. The algorithm exploits the four-channel (blue, green, red and near infrared) multispectral imaging capability of some terrestrial scanners using supervised, parametric classification to assign thematic class labels to all scan cloud points. Its principal advantage is that it is a completely data-driven algorithm and is independent of spatial sampling resolution since the processing is performed in four-dimensional spectral feature space. Its application to two data-sets of different spatial extent and spatial and spectral complexity is reported, for which respective overall classification accuracies of 87·0% and 82·0% were achieved. Analysis of the input data with emphasis on the characteristics pertinent to the anticipated outcomes precedes detailed analysis of the classification results and error sources and their causes. Erroneously classified points are attributed to radiometric errors stemming from both detector hardware and physical effects. 相似文献
3.
Angular resolution of terrestrial laser scanners 总被引：5，自引：0，他引：5
Knowledge of a laser scanner's spatial resolution is necessary in order to prevent aliasing and estimate the level of detail that can be resolved from a scanned point cloud. Spatial resolution can be decoupled into range and angular components. The latter is the focus of this paper and is governed primarily by sampling interval and laser beamwidth. However, emphasis is often placed on one of these—typically sampling interval—as an indicator of resolution. Since both affect the resolution of a scanned point cloud, consideration of only one factor independent of the other can lead to a misunderstanding of a system's capabilities. This will be demonstrated to be inappropriate except under very specific conditions. A new, more appropriate resolution measure for laser scanners, the effective instantaneous field of view (EIFOV), is proposed. It is derived by modelling the shift variance of the equal angular increment sampling process, laser beamwidth-induced positional uncertainty and observed angle quantisation with ensemble average modulation transfer functions (AMTFs). Several commercially available terrestrial laser scanner systems are modelled and analysed in terms of their angular resolution capabilities using the EIFOV. 相似文献
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6.
Derek D. Lichti 《GPS Solutions》2000,4(2):54-62
Kinematic differential Global Positioning System (DGPS) positioning is routinely used in industry for directly observing an
aircraft's position at each instant of photographic exposure during a photogammetric survey. A critical aspect of the subsequent
data processing is estimation of the aircraft position at the exact time of exposure. GPS measurements are acquired at a uniform
sampling rate, typically 1 Hz. The exposure times, however, do not generally coincide with these times. As a result, the exposure
station positions must be interpolated from the adjacent GPS positions. This is typically done using a low-order polynomial,
expressed as a function of time, for each coordinate dimension. However, trajectory perturbations induced by atmospheric turbulence
can render such interpolation methods ineffective.
This article will convey the results of an investigation into the use of several different interpolation models with airborne
GPS data during straight, level flight. The fundamental task of time series reconstruction will first be addressed, in which
several possible interpolation models are described. Two 10-Hz, airborne GPS data sets were collected to test the accuracy
of each model. The error properties resulting from the application of each model to these data will be presented and analyzed
in terms of time-domain statistics and frequency-domain characteristids. It will be demonstrated that interpolation error
can be significantly reduced, especially in the height dimension, through judicious choice of an interpolator. ? 2000 John
Wiley & Sons, Inc. 相似文献
7.
Derek D. Lichti Jacky Chow Herv Lahamy 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(3):317-326
One of the important systematic error parameters identified in terrestrial laser scanners is the collimation axis error, which models the non-orthogonality between two instrumental axes. The quality of this parameter determined by self-calibration, as measured by its estimated precision and its correlation with the tertiary rotation angle κ of the scanner exterior orientation, is strongly dependent on instrument architecture. While the quality is generally very high for panoramic-type scanners, it is comparably poor for hybrid-style instruments. Two methods for improving the quality of the collimation axis error in hybrid instrument self-calibration are proposed herein: (1) the inclusion of independent observations of the tertiary rotation angle κ; and (2) the use of a new collimation axis error model. Five real datasets were captured with two different hybrid-style scanners to test each method’s efficacy. While the first method achieves the desired outcome of complete decoupling of the collimation axis error from κ, it is shown that the high correlation is simply transferred to other model variables. The second method achieves partial parameter de-correlation to acceptable levels. Importantly, it does so without any adverse, secondary correlations and is therefore the method recommended for future use. Finally, systematic error model identification has been greatly aided in previous studies by graphical analyses of self-calibration residuals. This paper presents results showing the architecture dependence of this technique, revealing its limitations for hybrid scanners. 相似文献
8.
Derek Lichti 《The Photogrammetric Record》2002,17(99):481-492
This paper gives the results of an investigation into the use of different sampling rates and models for the interpolation of perspective-centre coordinates in GPS-assisted aerial triangulation. Industry-standard models and rigorous signal reconstruction filtering have been implemented for two largescale photogrammetric blocks. GPS sampling rate was found to have the most impact on bundle adjustment results in terms of the perspective-centre residuals. However, the accuracy of object-space point coordinates was found to be invariant to both GPS sampling rate and interpolation method 相似文献
9.
Derek D. Lichti 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(1):93-102
Instrument calibration is recognised as an important process to assure the quality of data captured with a terrestrial laser scanner. While the self-calibration approach can provide optimal estimates of systematic error parameters without the need for specialised equipment or facilities, its success is somewhat hindered by high correlations between model variables. This paper presents the findings of a detailed study into the sources of correlation in terrestrial laser scanner self-calibration for a basic additional parameter set. Several pertinent outcomes, resulting from experiments conducted with simulated data, and 12 real calibration datasets captured with a Faro 880 terrestrial laser scanner, are presented. First, it is demonstrated that panoramic-type scanner self-calibration from only two instrument locations is possible so long as the scans have orthogonal orientation in the horizontal plane. Second, the importance of including scanner tilt angle observations in the adjustment for parameter de-correlation is demonstrated. Third, a new network measure featuring an asymmetric distribution of object points that does not rely upon a priori observation of the instrument position is proposed. It is shown to be an effective means to reduce the correlation between the rangefinder offset and the scanner position parameters. Fourth, the roles of several other influencing variables on parameter correlation are revealed. The paper concludes with a set of recommended design measures to reduce parameter correlation in terrestrial laser scanner self-calibration. 相似文献
10.
The contribution of normal spiral galaxies to the high galactic latitude gamma-ray background >100 MeV is examined in the light of the estimates of its flux from the SAS-II measurements. The gamma-ray luminosity of each object is inferred from the known Milky Way value normalized to the corresponding optical quantity. Several possibilities are considered for the responsible physical production mechanism both diffuse and localized; they are then set to evolve with the galactic age according to three well-known evolutionary models. A final space-time integration leads to results which are expressed in the same unit as the measured background. It is seen that the model presented here can play an important role in the region > 100 MeV where the information on the spectral shape of the radiation is still very poor. Experimental tests for future gamma-ray observations are presented. 相似文献