Digital Grid Research Articles

Detection-Threshold Calibration and Other Factors Influencing Digital Measurements of Ground Cover

New methods of image acquisition and analysis are advancing rangeland assessment techniques. Most image-analysis programs require users to adjust detection thresholds for color or object classification, a subjective process we postulated would be influenced by human error and variation. We developed a ground-cover–measurement calibration procedure, the digital grid overlay (DGO), which is similar to image point sampling (dot grid) advanced by earlier researchers. We asked 21 rangeland professionals to measure ground cover using 2 subjective visual-estimate methods (threshold adjustment process, or TAP, and external [to the software] visual estimate, or EVE) and the DGO on 5 different nadir-view images of rangeland. We also compared cover measurements made by DGO-calibrated software in automated batch processing against DGO manual-only measurements. We found an unacceptable range of variation among rangeland professionals using TAP. The DGO and EVE values were more closely aligned. We discovered an age-related bias in bare-ground measurements: all users over 50 years of age classified more bare ground than did all users under 50 years of age when using TAP. One explanation for this bias is age-related yellowing of the eye lens. Manual DGO measurements required up to 15 minutes per image compared to about 1 second per image for automated computer analysis after software calibration. The greatest bare-ground difference between the DGO-calibrated software and manual DGO measurements for the data sets analyzed was 5.6% and the correlations imply that reasonably accurate automated measurements can be used for bare-ground measurements from digital-image data sets. The exception is where the software cannot adequately separate litter and bare ground. The digital methods we tested need improvement. However, external calibration (DGO or EVE) of current-generation image-analysis algorithms bring economical, statistically adequate monitoring of extensive land areas within the realm of practical application.

Circum-Antarctic palaeobathymetry: Illustrated examples from Cenozoic to recent times

We use a revised set of seafloor spreading isochrons and updated plate tectonic reconstructions to produce palaeo-age and basement depth grids for the Southern Ocean. The palaeo-depth maps illustrate the evolution of the ocean basins (widening and deepening) and oceanic gateway development surrounding Antarctica. We provide examples of palaeo-basement depth profiles at selected times between 45 Ma and the present across the Tasman Gateway and Drake Passage. The digital grids provide improved boundary conditions for palaeoceanographic circulation models as well as for backtracking sediments from ODP drilling.

ShanghaiGrid in action: the first stage projects towards digital city and city grid

The nearest goal of ShanghaiGrid is going to connect all supercomputers in this metropolis together to form a sharing environment for massive storage and grid computing. The first stage projects of ShanghaiGrid comprise four sub-projects, including: research on environment, protocols and standards of information grid infrastructure; development of system software for information grid and establishment of four major intra-grid nodes; development of peer-to-peer based virtual research platform; research on the application of grid based traffic-jam control and guidance. This paper introduces the background of ShanghaiGrid, provides a glimpse at features and challenges of its sub-projects, and summarises the general goal of them.

Detection-Threshold Calibration and Other Factors Influencing Digital Measurements of Ground Cover

New methods of image acquisition and analysis are advancing rangeland assessment techniques. Most image-analysis programs require users to adjust detection thresholds for color or object classification, a subjective process we postulated would be influenced by human error and variation. We developed a ground-cover-measurement calibration procedure, the digital grid overlay (DGO), which is similar to image point sampling (dot grid) advanced by earlier researchers. We asked 21 rangeland professionals to measure ground cover using 2 subjective visual-estimate methods (threshold adjustment process, or TAP, and external [to the software] visual estimate, or EVE) and the DGO on 5 different nadir-view images of rangeland. We also compared cover measurements made by DGO-calibrated software in automated batch processing against DGO manual-only measurements. We found an unacceptable range of variation among rangeland professionals using TAP. The DGO and EVE values were more closely aligned. We discovered an age-related bias in bare-ground measurements: all users over 50 years of age classified more bare ground than did all users under 50 years of age when using TAP. One explanation for this bias is age-related yellowing of the eye lens. Manual DGO measurements required up to 15 minutes per image compared to about 1 second per image for automated computer analysis after software calibration. The greatest bare-ground difference between the DGO- calibrated software and manual DGO measurements for the data sets analyzed was 5.6% and the correlations imply that reasonably accurate automated measurements can be used for bare-ground measurements from digital-image data sets. The exception is where the software cannot adequately separate litter and bare ground. The digital methods we tested need improvement. However, external calibration (DGO or EVE) of current-generation image-analysis algorithms bring economical, statistically adequate monitoring of extensive land areas within the realm of practical application.

Developing a Watershed Characteristics Database to Improve Low Streamflow Prediction

Information regarding topographic, meteorologic, geologic, and geomorphic characteristics is increasingly available in spa- tially explicit digital formats. Of interest is whether enhanced spatial processing of newly available digital grids can lead to new estimators of watershed characteristics which may in turn, improve our ability to predict extreme hydrologic events. Regional hydrologic models of low-flow processes often produce estimators with unacceptably large errors. Using a continuous digital elevation model ~DEM! of the conterminous United States, watershed boundaries were developed for the streamflow gauges of the USGS's Hydro-Climatic Data Network. Using these watershed boundaries, many watershed characteristics were developed from digital grids, including: the original DEM, the USDA's State Soil Geographic grids, and the Spatial Climate Analysis Service's orographically weighted precipitation and temperature grids of varying spatial and temporal resolution. Digital processing of grids leads to improvements in estimation and reproducibility of spatial statistics over traditional manual processing approaches. Low-flow regional regression models were developed for regions across the conterminous United States. Inclusion of the new watershed characteristics led to improvements in regional regression models for all regions. The inclusion of hydrogeologic indices, in particular a new smoothed baseflow recession constant estimator, led to dramatic improvements in low-flow prediction.

The regional magnetic data set of Namibia: Compilation, contributions to crustal studies and support to natural resource management

Research Article| December 01, 2002 The regional magnetic data set of Namibia: Compilation, contributions to crustal studies and support to natural resource management D.G. Eberle; D.G. Eberle Federal Institute for Geosciences and Natural Resources, P.O. Box 510153, 30631 Hannover, Germany, e-mail: detlef.eberle@bgr.de Search for other works by this author on: GSW Google Scholar G. Andritzky; G. Andritzky Federal Institute for Geosciences and Natural Resources, P.O. Box 510153, 30631 Hannover, Germany, e-mail: detlef.eberle@bgr.de Search for other works by this author on: GSW Google Scholar D.G. Hutchins; D.G. Hutchins Geological Survey of Namibia, P.O. Box 2168, Windhoek, Namibia, e-mail: dave@mme.gov.na; rainer@mme.gov.na Search for other works by this author on: GSW Google Scholar R. Wackerle R. Wackerle Geological Survey of Namibia, P.O. Box 2168, Windhoek, Namibia, e-mail: dave@mme.gov.na; rainer@mme.gov.na Search for other works by this author on: GSW Google Scholar Author and Article Information D.G. Eberle Federal Institute for Geosciences and Natural Resources, P.O. Box 510153, 30631 Hannover, Germany, e-mail: detlef.eberle@bgr.de G. Andritzky Federal Institute for Geosciences and Natural Resources, P.O. Box 510153, 30631 Hannover, Germany, e-mail: detlef.eberle@bgr.de D.G. Hutchins Geological Survey of Namibia, P.O. Box 2168, Windhoek, Namibia, e-mail: dave@mme.gov.na; rainer@mme.gov.na R. Wackerle Geological Survey of Namibia, P.O. Box 2168, Windhoek, Namibia, e-mail: dave@mme.gov.na; rainer@mme.gov.na Publisher: Geological Society of South Africa First Online: 07 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2003 Geological Society of South Africa South African Journal of Geology (2002) 105 (4): 361–380. https://doi.org/10.2113/1050361 Article history First Online: 07 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation D.G. Eberle, G. Andritzky, D.G. Hutchins, R. Wackerle; The regional magnetic data set of Namibia: Compilation, contributions to crustal studies and support to natural resource management. South African Journal of Geology 2002;; 105 (4): 361–380. doi: https://doi.org/10.2113/1050361 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract 41 airborne magnetic surveys flown between 1962 and 1992 over different areas of Namibia were compiled as part of a German-Namibian technical cooperation project to produce a refined compatible national (countrywide) magnetic data set. Contour maps are available in two scales (1:1 000 000 and 1:250 000) together with digital grids having cell sizes of 2000m, 500m and 200m. The refined magnetic data serve as a new tool suitable to elucidate the crustal evolution and to contribute to the management of renewable and non-renewable natural resources. Namibia can be subdivided into several magnetic domains amongst which the cratonic areas and the Proterozoic fold belts are the most important. Modelling indicates that the magnetic pattern reflects intra-continental rift and collision processes, most clearly on the periphery of the Archean cratons. The mid-Proterozoic, Sinclair Sequence is supposed to be an accreted terrane. Two examples of magnetic data used in the management of natural resources are discussed: Depth values of the top surface of the magnetic basement in the Otavi Mountainland provided by harmonic analysis of the magnetic field and synthesis of magnetization waves have contributed towards the development of a geohydraulic model of one of the most important aquifers of Namibia. In the southern part of the country, structural analysis of the magnetic field yielded intersections and confluences of magnetic lineaments, which are considered sites with future potential for hydrothermal mineralization. They especially cluster in the Proterozoic Sinclair Sequence and Orange River Group. A number of areas with increased mineral potential could be identified. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Nonorthogonal Halftone Screens

In color reproduction, the most troublesome moiré pattern is the second-order moiré, or the three-color moiré, usually produced by mixing of cyan, magenta and black halftone outputs. A classical 3-color zero-moiré solution is using three identical cluster halftone screens with different rotations: 15°, 45° and 75°, respectively. However, for most digital printing devices, the size and shape of halftone screens are constrained by the “digital grid”, which defines the locations of printed dots, and therefore, an exact 15° or 75° rotation of a cluster screen is impossible. Although there are many alternative approaches for moiré-free color halftoning, most of them only provide approximate solutions and/or have a tendency to generate additional artifacts associated with halftone outputs. The difficulty to achieve moiré-free color halftoning is greatly relieved by using nonorthogonal halftone screens, i.e., screens in general parallelogram shapes. As a matter of fact, there exist many practical solutions by combining three simple nonorthogonal halftone screens. In this paper, a general condition for 3-color zero-moiré solutions is derived. A procedure using integer equations to search practical solutions for different applications is also described.

傾斜地の標高補間に用いられる３次エルミート関数の性質について

The cubic Hermite function was used as an interpolation method to generate the Digital Map 50m Grid (Elevation) by the Geographical Survey Institute of Japan. A Few studies have been reported concerning the reliability of cubic Hermite function for slope interpolation. However, these studies were mostly based on empirical observations without discussions about the cubic Hermite function's mathematical properties. In this paper, we investigate the applicability of the cubic Hermite function for slope interpolation using the mathematical relations between the trajectories of the cubic Hermite function and its tangent values at the both ends of the interpolation interval. The result shows that a proper slope interpolation can be achieved if and if only the trajectories' values are up to three times of the tangent's value.

Southern hemisphere palaeobathymetry

Abstract Digital grids, with a spatial resolution of 0.5°, were compiled using bathymetry, sediment thickness and oceanic crustal ages for the southern hemisphere to calculate sediment-free palaeobathymetric charts for late Cretaceous (110 Ma) to the present. These reconstructions allow the definition and quantification of the bathymetric evolution of the seaways and gateways within this region. Pre-60 Ma the palaeobathymetry and the interconnection of the deeper ocean basin was dominated by the formation of hotspot-related ridges and plateaux. Between 40 Ma and the present the palaeobathymetry is characterized by the opening of numerous gateways as the Tasman Rise separated from Antarctica, the Mascarene Plateau split from the Chagos—Laccadive Ridge, Broken Ridge rifted from the northern Kerguelen Plateau, the Crozet Plateau separated from the Madagascar Ridge, and the Scotia Sea opened. The validity of these palaeobathymetric reconstructions is demonstrated by comparing the digital gridded data sets, from which they were calculated, with data derived from 39 Deep Sea Drilling Project and Ocean Drilling Program drill sites. Comparison of drill site data with the gridded data revealed positive correlations between crustal ages and bathymetry, whereas the sediment thickness data showed no correlation. The lack of any correlation for the sediment thickness data, however, did not preclude a positive correlation between sediment-free bathymetries. The difference between expected ‘true’ palaeobathymetry, that is with sediments older than the time of reconstruction decompacted and reloaded back onto oceanic crust, and the sediment-free palaeobathymetry was shown to be less than 600 m for 87.5% of the data. The greatest differences occur where sediment thicknesses are greatest, i.e. within the deep ocean basins which are in close proximity to the continental margin.

Digital isochrons of the world's ocean floor

We have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self‐consistent set of global isochrons and associated plate reconstruction poles. The age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading. Ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models. We have constructed an age grid with error estimates for each grid cell as a function of (1) the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid, (2) the distance of a given grid cell to the nearest magnetic anomaly identification, and (3) the gradient of the age grid: i.e., larger errors are associated with high age gradients at fracture zones or other age discontinuities. Future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere, the heat loss of the Earth, ridge‐push forces through time, asymmetry of spreading, and providing constraints for seismic tomography and mantle convection models.

Comment on “Digital Elevation Model Grid Size, Landscape Representation, and Hydrologic Simulations’ by Weihua Zhang and David R. Montgomery

Comment on “Digital Elevation Model Grid Size, Landscape Representation, and Hydrologic Simulations’ by Weihua Zhang and David R. Montgomery

Reply [to “Comment on ‘Digital Elevation Model Grid Size, Landscape Representation, and Hydrologic Simulations’ by Weihua Zhang and David R. Montgomery”

Reply [to “Comment on ‘Digital Elevation Model Grid Size, Landscape Representation, and Hydrologic Simulations’ by Weihua Zhang and David R. Montgomery”

Compilation of the Namibian airborne magnetic surveys: procedures, problems and results

Forty one airborne magnetic surveys flown between 1962 and 1992 over different areas of Namibia, with a total of about 700,000 km, have been compiled as part of a German-Namibian co-operation project to produce a refined compatible countrywide magnetic data set. It was required to compile the data as if the whole country was flown by a single survey at 100 m terrain clearance at the same magnetic epoch. Emphasis was therefore given to the selection of the magnetic reference field model. The creation of a digital terrain model (DTM) was compulsory. Levelling of the survey blocks was impeded since adjacent blocks were only rarely overlapping. The magnetic data set is available as both coloured contour maps (scales 1:250 000 and 1:1 000 000) and digital grids with varying cell sizes (2000 m, 500 m and 200 m). Shield areas, fold belts and anorogenic intrusions dominate the magnetic anomaly pattern of Namibia. The fold belts are characterized by parallel running, narrow (<100 km) magnetic and virtually non-magnetic zones. Shield areas, covered by a thick sequence of mostly non-magnetic sediments, are distinguished by broad, mid-amplitude anomalies with low gradients. The analysis of magnetic linear features reveals the existence of two directional sets of magnetic lineations running across both fold belts and shield areas.

Simulating the grassfire transform using an active contour model

A method for shape description of planar objects that integrates both region and boundary features is presented. The method is an implementation of a 2D dynamic grassfire that relies on a distance surface on which elastic contours minimize an energy function. The method is based on an active contour model. Numerous implementation aspects of the shape description method were optimized. A Euclidean metric was used for optimal accuracy, and the active contour model permits bypassing some of the discretization limitations inherent in using a digital grid. Noise filtering was performed on the basis of both contour feature measures and region measures, that is, curvature extremum significance and ridge support, respectively, to obtain robust shape descriptors. Other improvements and variations of the algorithmic implementation are proposed. >

Magnetic imprints of continental accretion in the U.S.S.R

The evidence for these events has been studied extensively by Soviet investigators, who in recent years have applied the concepts of plate tectonics to the geological framework and evolution of the continental U.S.S.R. and summarized their findings in a series of tectonic reconstructions. The results of these studies have been synthesized, and their English publication “e.g., Khain, 1987; Zonenshain et al, 1990a,b” has provided Western investigators with a modern and comprehensive overview of the geological structure and history of the Soviet Union.Complementing these recent publications is a new digital grid of about 16 million points describing the magnetic anomaly field of the U.S.S.R. This data set was produced from a series of 18 maps, scale 1:2,500,000, published by the U.S.S.R. Ministry of Geology “Makarova, 1974” and digitized recently by the U.S. Naval Oceanographic Office in Bay St. Louis, Miss.

Watersheds in digital spaces: an efficient algorithm based on immersion simulations

A fast and flexible algorithm for computing watersheds in digital gray-scale images is introduced. A review of watersheds and related motion is first presented, and the major methods to determine watersheds are discussed. The algorithm is based on an immersion process analogy, in which the flooding of the water in the picture is efficiently simulated using of queue of pixel. It is described in detail provided in a pseudo C language. The accuracy of this algorithm is proven to be superior to that of the existing implementations, and it is shown that its adaptation to any kind of digital grid and its generalization to n-dimensional images (and even to graphs) are straightforward. The algorithm is reported to be faster than any other watershed algorithm. Applications of this algorithm with regard to picture segmentation are presented for magnetic resonance (MR) imagery and for digital elevation models. An example of 3-D watershed is also provided. >

A new parameterization of digital straight lines

A 1:1 correspondence is established between digital straight lines which start at a fixed point and a simple set of quadruples of integer parameters. Such a representation by parameters is useful for enumeration, First, the authors show a 1:1 correspondence between point pairs in a planar set of points and the linear dichotomies of this set. Then, from the equivalence between digital lines and linear dichotomies of points on the digitization grid, they prove a 1:1 and 'onto' correspondence between digital straight lines starting at a fixed point and a well-defined set of pairs of grid points. It follows that four parameters uniquely represent any given digital line with a fixed starting point. An O(N) algorithm is given for determining the parameters from the digital line, as well as O(log N) algorithms for transforming between these parameters and the parameters suggested by L. Dorst and A.W.M. Smeulders (1984).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Drug and alcohol attitudes and usage among elementary and secondary students

Overflights, especially low-level flights, have a measurable impact on the acoustic environment of the areas they traverse. This is of particular concern to protected areas with a mission of protecting natural resources, cultural resources, and the visitor experience. Yet, understanding overflight travel patterns at parks and protected areas has proven difficult to determine. Recent technology makes it possible to collect accurate overflight data allowing researchers to quantify travel patterns across a protected area. Location data, including x, y, and z data, can be used to quantitatively assess effects of overflights and to inform solutions to protect resources and the visitor experience. Therefore, the purpose of this study was to spatiotemporally quantify overflight travel patterns at Hawai'i Volcanoes National Park using data derived from Automatic Dependent Surveillance-Broadcast (ADS-B) technology. Location data, a digital grid, and hot spot clustering were used to identify spaces with a statistically-significant high volume of overflights. Some of these spaces overlap with terrestrial visitor attraction locations, suggesting potential for degraded visitor experience. Specifically, results indicate a spatial trend of low-flying overflights along the eastside of the park, a high volume of overflights near Nāpau Trailhead and Nāpau Crater, and spatial clustering of overflights varies across hour of the day. The described methods provide a foundation for future research and the results are useful for informing the designation of lateral and minimum altitude parameters for low-level overflights such as air tours.

Digital plane and grid point segments

Digital plane and grid point segments are studied in parameter space. Concepts and results on digital straight line segments are extended to two dimensions. Properties of the domain in parameter space of the digital objects are derived. An algorithm, linear in the number of points, to obtain the domain of a given digital object is given. The connection with Diophantine approximations from the theory of numbers is established, number theoretical results are used and approximation algorithms are reviewed for our purpose. Application of the concept of digital grid point segments to processing of halftone pictures is outlined.

Digital plane and grid point segments

Digital plane and grid point segments