Regular Raster Research Articles

Extraction of Step-Feature Lines in Open-Pit Mines Based on UAV Point-Cloud Data

Step-feature lines are one of the important geometrical elements for drawing the status quo maps of open-pit mines, and the efficient and accurate automatic extraction and updating of step-feature lines is of great significance for open-pit-mine stripping planning and analysis. In this study, an automatic extraction method of step-feature lines in an open-pit mine based on unmanned-aerial-vehicle (UAV) point-cloud data is proposed. The method is mainly used to solve the key problems, such as low accuracy, local-feature-line loss, and the discontinuity of the step-feature-line extraction method. The method first performs the regular raster resampling of the open-pit-mine cloud based on the MLS algorithm, then extracts the step-feature point set by detecting the elevation-gradient change in the resampled point cloud, further traces the step-feature control nodes by the seed-growth tracking algorithm, and finally generates smooth step-feature lines by fitting the space curve to the step-feature control nodes. The results show that the method effectively improves the accuracy of step-feature-line extraction and solves the problems of local-feature-line loss and discontinuity.

Reduction of mid-spatial frequency errors on aspheric and freeform optics by circular-random path polishing.

Pseudo-random paths are a useful tool to reduce mid-spatial frequency errors created in the processing of optical surfaces by sub-aperture polishing tools. Several types of patterns have been proposed, including hexagonal, square and circular, but prior literature has largely focused on flat and gently curved surfaces. Here, an extension of the circular-random path to strongly curved aspheric and freeform surfaces is proposed. The main feature of the algorithm is to cover the entire surface to be polished with a uniformly distributed tool path. Aspheric condenser lenses are then polished with a regular raster and circular-random path. Analysis of the optical performance shows that the random path can reduce the amplitude of mid-spatial frequency errors and relative intensity of satellite images. These features are particularly desirable in short wavelength applications, such as mirrors for EUV and X-ray.

A design of raster plot for illustrating dynamic neuronal activity during deep brain stimulation

Deep brain stimulation (DBS), which usually utilizes high frequency stimulation (HFS) of electrical pulses, is effective for treating many brain disorders in clinic. Studying the dynamic response of downstream neurons to HFS and its time relationship with stimulus pulses can reveal important mechanisms of DBS and advance the development of new stimulation modes (e.g., closed-loop DBS). To exhibit the dynamic neuronal firing and its relationship with stimuli, we designed a two-dimensional raster plot to visualize neuronal activity during HFS (especially in the initial stage of HFS). Additionally, the influence of plot resolution on the visualization effect was investigated. The method was then validated by investigating the neuronal responses to the axonal HFS in the hippocampal CA1 region of rats. Results show that the new design of raster plot is able to illustrate the dynamics of indexes (such as phase-locked relationship and latency) of single unit activity (i.e., spikes) during periodic pulse stimulations. Furthermore, the plots can intuitively show changes of neuronal firing from the baseline before stimulation to the onset dynamics during stimulation, as well as other information including the silent period of spikes immediately following the end of HFS. In addition, by adjusting resolution, the raster plot can be adapted to a large range of firing rates for clear illustration of neuronal activity. The new raster plot can illustrate more information with a clearer image than a regular raster plot, and thereby provides a useful tool for studying neuronal behaviors during high-frequency stimulations in brain.

A method to correct hysteresis of scanning probe microscope images based on a sinusoidal model.

Piezoelectric actuators are widely used in scanning platforms of scanning probe microscopes (SPMs). However, the hysteresis of piezoelectric actuators reduces positioning accuracy and results in distorted SPM images. When regular raster scanning of SPM starts, the piezoelectric actuators move repeatedly at the same scanning range and frequency once the scanning parameters are set. In this study, a practical and simple mathematical model derived from experimental phenomenon, which is the combination of sinusoidal and linear functions, was proposed to describe the hysteresis behavior of piezoelectric actuators with repeated scanning. The model parameter was calculated from the coordinates of matched feature points in the trace and retrace images of ordinary sample obtained with an atomic force microscope (AFM). Experimental results show that the hysteresis of the scanned images is decreased from 107.46 pixels to 2.50 pixels after correction, with a width of 800 pixels. Hysteresis in other scanned images with different scanning frequencies and ranges was also corrected effectively using this model. The proposed model can be used to correct the hysteresis of AFM images without using any expensive displacement sensors or standard samples. The model is suitable and easy to be integrated into the scanning program of AFM without requiring hardware modifications.

Comparison of interpolation methods and image correlation in the collection of data for digital elevation model

Digital Relief Model (DRM) is the name used officially in Croatia, and we distinguish between the original and derived DRM. Referring to the regular raster structure of elevations stored in the derived DRM, the term digital elevation model (DEM) was used for this model. Three geomorphometrically different landscapes have been tested. The elevation points were created using two methods, interpolation from the data obtained in the photogrammetric survey and image correlation, in two resolutions (5x5 and 25x25 meters). The paper presents the differences in the application of two methods of calculating DEM. The causes of differences discussed and the relative estimation of the accuracy of each method elaborated by comparing the height of points on new models with the heights on original DRM. The recommendation for the usage of the acceptable method is given related to the accuracy, the speed of data collection and a higher degree of automation.

PŘESNOST DIGITÁLNÍHO MODELU TERÉNU A JEHO VYUŽITÍ V LESNICTVÍ

Digital terrain model (DTM) is considered as an important geospatial data layer. At the present in the Czech Republic, digital contour data sources are often used for constructing regular raster DTM; the initial process requires interpolation between the points in order to estimate values in a regular grid pattern. The commonly used data sources are: the Primary Geographic Data Base (ZABAGED), the Digital Territory Model (DMÚ25) and eventually the Regional Plans of Forest Development (OPRL). In this paper, some constructions of DTM based on the above mentioned data were tested using several software products. Algorithm parameters can be optimized in several ways; in this sense the most useful operations proved comparing the first and second derivative of DTM and its real appearance in terrain and using cross-validation procedure or terrain data measurements to compute and minimize the root mean square error values (RMSE). The Forest Training Enterprise “Masaryk Forest” was the area for the experimental optimization of DTM.

4-D Statistical Surface Method for Visual Change Detection in Forest Ecosystem Simulation Time Series

Rising uncertainties associated with climate change compel forest management planning to include forest ecosystem simulations. The output of such models is often of high spatio-temporal complexity and difficult to interpret for the user. This contribution describes a novel visualization method called four-dimensional (4-D) statistical surfaces, which aims at improving the visual detection of change in time series. The method visualizes attribute values as surfaces, which are interpolated and animated over time; the interactive attribute surfaces are combined with color-coding and contour lines to support absolute and relative height judgment as well as faster perception and better location of change. A design study and prototypical implementation of the visualization method is described in this contribution. Time-series simulation results of LANDIS-II, a commonly used modeling tool in forest ecology, as well as a temporal vegetation index dataset (NDVI) are visualized using 4-D statistical surfaces. Usability challenges are addressed based on explorative interviews with a small group of users. The method is not limited to ecological model output; it can be used to create three-dimensional (3-D) temporal animations of arbitrary time-series datasets where parameters are supplied in regular raster format.

Optimisation of global grids for high-resolution remote sensing data

Upcoming remote sensing systems onboard satellites will generate unprecedented volumes of spatial data, hence challenging processing facilities in terms of storage and processing capacities. Thus, an efficient handling of remote sensing data is of vital importance, demanding a well-suited definition of spatial grids for the data׳s storage and manipulation. For high-resolution image data, regular grids defined by map projections have been identified as practicable, cognisant of their drawbacks due to geometric distortions. To this end, we defined a new metric named grid oversampling factor (GOF) that estimates local data oversampling appearing during projection of generic satellite images to a regular raster grid. Based on common map projections, we defined sets of spatial grids optimised to minimise data oversampling. Moreover, they ensure that data undersampling cannot occur at any location. From the resulting GOF-values we concluded that equidistant projections are most suitable, with a global mean oversampling of 2% when using a system of seven continental grids (introduced under the name Equi7 Grid). Opposed to previous studies that suggested equal-area projections, we recommend the Plate Carrée, the Equidistant Conic and the Equidistant Azimuthal projection for global, hemispherical and continental grids, respectively.

A global exposure model for disaster risk assessment

The Global Exposure database is being produced for the Global Risk Assessment 2013, part of the Global Assessment Report 2013 (GAR 2013). It aims to map at a granular geographical level the world׳s capital stock in urban areas. It is designed primarily to assess the risk of economic losses as consequence of natural hazards at a global scale.The Global Exposure database for GAR 2013 (GEG-2013) is an open exposure global dataset at 5km spatial resolution which integrates population and country-specific building typology, use and value. It is currently suitable mainly for earthquakes and cyclones probabilistic risk modeling using the CAPRA platform (http://www.ecapra.org).This paper describes the development of the GEG-2013. The database is based on a top-down or “downscaling” approach of national/regional socio-economic and building type information. These information are transposed onto a regular raster dataset (grid format) using a geographic population distribution model as a proxy.

Дослідження ефективності застосування адаптивного метода растрування у флексографському способі друку

The work is devoted to investigation of problem of decline in the quality of tone reproduction on reprint at the expense of extension of printing elements length on a flexo plate in the direction of printing, arising from the deformation of elastic photopolymer form when it is fastening at the plate cylinders of printing machine.In the work the geometrical model to calculate the elongation of halftone dot proposed, to verify it’s adequacy in the experimental research parameters of the original and distorted dot of a regular raster was studied. For the experiment, established the dependence of magnitude of distortion of the dot from the screen frequency and angle of the raster of image on reprint, printed with flexographic form.Based on an analysis of the results developed a method of compensation for distortion of the printing elements that minimizes it’s influence on the quality of imaging.

Reducing scale dependence in TOPMODEL using a dimensionless topographic index

Abstract. This paper stems from the fact that the topographic index used in TOPMODEL is not dimensionless. In each pixel i in a catchment, it is defined as xi=ln(ai/Si), where ai is the specific contributing area per unit contour length and Si is the topographic slope. In the SI unit system, ai/Si is in meters, and the unit of xi is problematic. We propose a simple solution in the widespread cases where the topographic index is computed from a regular raster digital elevation model (DEM). The pixel length C being constant, we can define a dimensionless topographic index yi=xi-lnC. Reformulating TOPMODEL equations to use yi instead of xi helps giving the units of all their terms and emphasizes the scale dependence of these equations via the explicit use of C outside from the topographic index, in what can be defined as the transmissivity at saturation per unit contour length T0/C. The term lnC defines the numerical effect of DEM resolution, which contributes to shift the spatial mean x of the classical topographic index when the DEM cell size C varies. A key result is that both the spatial mean y of the dimensionless index and T0/C are much more stable with respect to DEM resolution than their counterparts x and T0 in the classical framework. This shows the importance of the numerical effect in the dependence of the classical topographic index to DEM resolution, and reduces the need to recalibrate TOPMODEL when changing DEM resolution.

In-Flight Spectral Characterization and Calibration Stability Estimates for the Clouds and the Earth’s Radiant Energy System (CERES)

Abstract It is essential to maintain global measurements of the earth radiation budget (ERB) from space, the scattered solar and emitted thermal radiative fluxes leaving the planet. These are required for the purpose of validating current climate model predictions of the planet’s future response to anthropogenic greenhouse gas forcing. The measurement accuracy and calibration stability required to resolve the magnitude of model-suggested cloud–climate feedbacks on the ERB have recently been estimated. The suggestion is for ERB data to strive for a calibration stability of ±0.3% decade−1 for scattered solar, ±0.5% decade−1 for emitted thermal, and an overall absolute accuracy of 1 W m−2. The Clouds and the Earth’s Radiant Energy System (CERES) is currently the only satellite program to make global ERB measurements, beginning in January 1998. However, the new climate calibration standards are beyond those originally specified by the NASA CERES program for its edition 2 data release. Furthermore, the CERES instrument optics have been discovered to undergo substantial in-flight degradation because of contaminant issues. This is not directly detectable by using established calibration methods. Hence, user-applied revisions for edition 2 shortwave (SW) data were derived to compensate for this effect, which is described as “spectral darkening.” Also, an entirely new in-flight calibration protocol has been developed for CERES that uses deep convective cloud albedo as a primary solar wavelength stability metric. This is then combined with a sophisticated contamination mobilization/polymerization model. The intention is to assign spectral coloration to any optical degradation occurring to the different CERES Earth observing telescopes. This paper quantifies the stability of revised edition 2 data. It also calculates stability, which the new protocols could give CERES measurements if used. The conclusion is that the edition 2 revisions restore the originally specified stability of CERES SW data. It is also determined that the climate calibration stability goals are reachable by using the new in-flight methodologies presented in this paper. However, this will require datasets of longer than approximately 10 yr. It will also require obtaining regular raster scans of the Moon by all operational CERES instruments.

Perceptually Transparent Polyline Watermarking Based on Normal Multi-Resolution Representation

Digital watermarking techniques were developed for regular raster data such as images or video, but little research addressed irregular vector data, such as the shapes of cartoons or elevation contours. Vector graphic images, such as those in SVG format, are popular on the WWW, and provide the advantage of permitting affine transformations without aliasing. The creation of cartoon images or the acquisition of GIS geometry data involves much work, so the copyright and ownership of vector data must be protected. Common components in vector graphic images are polygonal lines or polylines. This work develops a normal multi-resolution representation of a polygonal line, and embeds a copyright notice or serial number in this representation. Previous studies on polyline watermarking have the non-transparent problems, including self-intersection of line segments. The experimental results demonstrate that the proposed watermarking approach is perceptually transparent, and solves the self-intersection problem. It is also resistant to similarity transformation, traversal reordering, point insertion/deletion and random noise attacks.

Optimization of digital terrain model for its application in forestry

Digital terrain model (DTM) represents a very important geospatial data type. In the CzechRepublic, the most common digital contour data sources are the Primary Geographic Data Base (ZABAGED), the Digital Ground Model (DMÚ25) and eventually the Regional Plans of Forest Development (OPRL). In constructing regular raster DTM, the initial process requires interpolation between the points in order to estimate values in a regular grid pattern. In this study, constructions of DTM from the above-mentioned data were tested using several software products: ArcEditor 9.0, Atlas 3.8, GRASS 6.1, Idrisi 14.02 and TopoL 2001. Algorithm parameters can be optimized in several ways. In this sense a comparison of the first and second derivative of DTM and its real appearance in the terrain and a cross-validation procedure or terrain data measurements to compute and minimize the root mean square error values (RMSE) proved to be the most useful operations. The ZABAGED contour data provided the best results, with software specific algorithms for interpolations of contour data (ArcGIS Desktop Topo to Raster, Idrisi Kilimanjaro TIN).

A GIS-based simulation model for terrain tractability

The paper describes a concept for a GIS-based terrain tractability model and an optimal off-road routing. The general structure of the model is based on an object model which uses the cost surface technique to describe actual conditions in the terrain. The cost surface is a kind of mobility index and it is based, e.g., on vehicle, wheel, terrain, tree coverage, road and weather objects. Different cost surface alternatives can be generated according to changing information in objects. A regular raster analysis is used to determine alternative routes in different conditions. It has been shown that the adequate number of useful parameters can be found from national level digital maps to support off-road analyses.

Terrain modeling in forward gravimetric problems: a case study on local terrain effects

The computation of the gravitational effect of a known density distribution at an arbitrary point in space is a common task in forward modeling and enters many routine applications in geophysical prospecting and exploration geophysics. The availability of data banks with gravity, terrain and, lately, density data, covering with a rather high resolution large areas mainly of the continental part of the planet, permits the evaluation of gravity field-related quantities not only at individual, but also at normally distributed target points laid on a regular raster. The role of the different geometric approximations used for the representation of the topographic relief is investigated in the frame of several methodologies for the computation of the same quantity: the vertical component of the gravitational attraction resulting from the given masses of a digital elevation model (DEM) assuming a constant density value. The considered methods include the right rectangular prism, the general polyhedron, the mass line and the mass prism FFT methods. Between these purely numerical, purely analytical and hybrid solutions, discrepancies of up to several milligal were detected, using the data of a fairly dense DEM of a part of the Bavarian Alps. The numerical investigations which were carried out using all the above techniques established the polyhedral modeling as the most accurate, flexible and, under circumstances, efficient method for the computation of local gravimetric terrain effects.

Phenomenon‐based Specification of the Digital Representation of Terrain Surfaces

The phenomenon known as ‘terrain’ is a continuous surface. However, when a digital terrain representation is based on a regular raster (i.e. a DEM) the digital surface is commonly not continuous. This is the case for the derivation of variables such as slope, aspect, and curvature values as performed in today's Geographic Information Systems (GIS). Often, there is no surface specified at all, as, for instance, when flow lines or watersheds are constructed. The discrepancy between the phenomenon to be modelled and its digital representation causes the terrain analysis results to be less accurate than they could be. Furthermore, if more than one type of terrain information is derived the results are likely to be based on different specifications of the seemingly same terrain surface. The combined application of the derivation results will likely introduce inconsistencies. This paper suggests founding the specification of digital terrain representations on a careful analysis of the properties of the phenomenon. The paper details the reasons for, and advantages of, continuous surface representations and emphasises the importance of a comprehensive documentation of the conceptual models underlying digital terrain representations. A review of suitable interpolation approaches for the specification of terrain surfaces is given. The paper discusses how the resulting digital surfaces are analysed and how measurement uncertainty may be accounted for.

Topology in Raster and Vector Representation

Egenhofer’s nine-intersection, well-known for vector representations, is defined here on a raster, using a hybrid raster model, and then systematically transformed to yield functions which can be used in a convolution operation applied to a regular raster representation. Applying functions, the hybrid raster elements need not be stored. It becomes thus possible to determine the topological relation of two regions, given in raster representation, with the same reasoning as in vector representations. This contributes to the merging of raster and vector operations. It demonstrates how the same conceptual operations can be used for both representations, thus hiding in one more instance the difference between them.

Model-based matching and hinting of fonts

In today's digital computers, phototypesetters and printers, typographic fonts are mainly given by their outline descriptions. Outline descriptions alone do not provide any information about character parts like stems serifs, shoulders, and bowls. But, in order to produce the best looking characters at a given size on a specific printer, non-linear operations must be applied to parts of the character shape. At low-resolution, grid-fitting of character outlines is required for generating nice and regular raster characters. For this reason, grid-fitting rules called hints are added to the character description. Grid-fitting rules require as parameters certain characteristic points within the shape outlines. In order to be able to detect these characteristic points in any given input font, a topological model representing the essence of the shapes found in typographic latin typefaces is proposed. This model includes sufficient information for matching existing non-fancy outline fonts to the model description. For automatic hint generation, a table of applicable hints is added into the topological model description. After matching a given input shape to the model, hints which can be applied to the shape of the given font are taken and added to its outline description. Furthermore, a structural description of individual letter shape parts using characteristic model points can be added to the model. Such a description provides knowledge about typographic structure elements like stems, serifs and bowls.

Two-oscillator scan stability

MANY are familiar with raster patterns, particularly the example seen on the face of television receivers. In order to present the most picture information with least bandwidth, such regular raster patterns are stabilized by synchronizing signals, derived by subdividing the frequency produced by a piezoelectric crystal stabilized oscillator. However, the simplicity of using an independent, stable oscillator for each of the vertical and horizontal deflection waves has been appealing. This was especially so for the extensive circuitry and subdivision needed to furnish the high-speed scans and quadruple interlace required when Avion-Alexandri carried out a U.S. Air Force RADC contract to pursue the experiments in electronic image processing done at the National Bureau of Standards. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup>