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Remote Sensing
Published in Julio Sanchez, Maria P. Canton, William Perrizo, Space Image Processing, 2018
Julio Sanchez, Maria P. Canton
Local factors of an image feature are often termed context operators. Elevation is probably the most commonly used context operator. Topographic maps show lines that link points of the same elevation. A digital elevation model (DEM) is the computerized version of a topographic map. Neighborhood factors are also considered context operators and new layers are derived taking into consideration neighborhood and proximity conditions. For example, Figure 1.11 shows a new boolean layer b which is based on selecting the larger lakes and ponds in image a. In this case, the processing logic uses a neighborhood algorithm to determine if a group of related pixels meets the size requirement specified in the filter. Such digital filters are often available in a GIS and in other raster image processing products.
Chapter 1
Published in Pearson Frederick, Map Projections:, 2018
The terms large scale vs. small scale come from consideration of the fraction dm/de. A scale of 1/10,000 is a large scale, and 1/1,000,000 is a small scale. A plan, or a map showing buildings, cultural features, or boundaries is usually 1/10,000 or larger. A topographic map, which gives roads, railroads, towns, contour lines, and other details, has a scale between 1/10,000 and 1/1,000,000. Maps of a scale smaller than 1/1,000,000 are atlas maps. These maps delineate countries, continents, and oceans. The scale factor, S, or principal scale, is used in the plotting equations of Chapters 4, 5, and 6.
Topographic Map Reading
Published in Peter Hancock, John Flach, Jeff Caird, Kim Vicente, Local Applications of the Ecological Approach to Human-Machine Systems, 2018
H. L. Pick, M. R. Heinrichs, D. R. Montello, K. Smith, C. N. Sullivan, W. B. Thompson
Topographic maps are the relatively familiar form of geographic maps in which elevation is represented by contour lines connecting locations of equal elevation. These can be, and are, used as navigational aids for helping to solve quite sophisticated forms of way-finding problems. The present chapter is concerned with how such maps are used for solving localization problems. However, before addressing specifically how topographic maps are used, it is worthwhile to consider such technological aids in the general context of navigation.
Effects of land use and land cover change on soil erosion potential in Berhe district: a case study of Legedadi watershed, Ethiopia
Published in International Journal of River Basin Management, 2022
Mehari Mariye, Melesse Mariyo, Yang Changming, Zebene Lakew Teffera, Brhane Weldegebrial
These topographic maps had been colour-coded for different land covers which include; reservoir, road, Settlement, streams and forest area. The boundary of the watershed was delineated based on these topographic maps of contour lines (represents a ground elevation or vertical distance above a reference point such as sea levels) and contour interval (the difference in elevation between two adjacent contours). Acquired Multi-temporal (1985, 1997 and 2013) satellite imagery of the study area has been imported to ERDAS 9.2 image processing software. Digital Image processing and classification technique have been done using ERDAS Imagine 9.2. The classified images have been used in the extraction of information on the land cover condition and statistical quantification of changes over the last three decades. The satellite images of each band in each year (1985, 1997 and 2013) have been stacked in ERDAS 9.2 within interpreter main icon utilities with layers stacked function. Then, from the stacked satellite images the study area image has been extracted by clipping the area of interest layer of the study shape file from GIS in Arc GIS 10.2 software. We applied different pre-processing techniques such as geometric correction, radiometric corrections, and Lambertian correction to minimize the depiction of vicissitudes due to misregistration and environmental and sensor dissimilarities between the images and to make the multi-date imagery radio metrically consistent. Image of both dates was geo-referenced with respect to each other by collecting high-quality ground control points, and the total RMSE error of geo-referencing was kept below 0.2 pixels.
Vertical accuracy evaluation of freely available latest high-resolution (30 m) global digital elevation models over Cameroon (Central Africa) with GPS/leveling ground control points.
Published in International Journal of Digital Earth, 2019
Loudi Yap, Ludovic Houetchak Kandé, Robert Nouayou, Joseph Kamguia, Nasser Abdou Ngouh, Marie Brigitte Makuate
Digital Elevation Models (DEMs) contain topographic data that are vital for many scientific, technical, and other applications. Among these applications, there are land researches (geomorphology, monitoring active volcanoes and observing eruptions (Vassilopouloua et al. 2002; Bisson et al. 2016), geological activities in mountainous and flat areas (Azzaro et al. 2012; Rebai et al. 2013), monitoring coastal erosions and sedimentations (Du et al. 2012, 2015; Wadey, Nicholls, and Hutton 2012; de Vente et al. 2013), etc …). There are also sea area and land water area researches (Pekel et al. 2016), analysis of sea surface temperatures of coastal zones, mapping and database creation of coral reef (Hedley et al. 2016; Hamylton 2017, etc …), snow, ice (monitoring of glacier (Kääb 2005; Fujita et al. 2008; Lenzano 2013; Liu et al. 2016)) and atmosphere studies (monitoring of clouds and ice in polar regions (Cook et al. 2012; Brunt et al. 2014; Li et al. 2015), research on types of cloud formation, etc.). Even when they are used indirectly in a study, topographic data are sometimes introduced in preparing visualization tools such as perspective or stereoscopic terrain views. DEMs are a set of heights of points, defined with respect to a specific reference system, and generally presented in the form of a digital raster file, or an ASCII text grid file. In these files, heights of unknown points can be interpolated. DEMs are also used to generate contour lines (representing specific height values) on topographic maps, where they can be easily interpreted in terms of the earth’s topography shape. These heights can also be used for 3D reconstitution of the real earth topography (terrain only), or 3D modeling accounting for the upper surface of the landscape. In the first case, the DEM is a Digital Terrain Model (DTM) and in the second, it is a Digital Surface Model (DSM), accounting for vegetation heights, buildings and other surface features. DTMs and DSMs are therefore identical in areas with no ground cover. However, most data providers and professional users use the term DEM for both DTM and DSM (Varga and Bašić 2015).