Relief Modelling and Digital Elevation Model (DEM) PDF

RELIEF MODELLING AND DIGITAL ELEVATION 4.​ Requires workers to have considerable training and MODEL (DEM) practice 4.​ LAYER TINTS RELIEF METHODS...

RELIEF MODELLING AND DIGITAL ELEVATION 4.​ Requires workers to have considerable training and MODEL (DEM) practice 4.​ LAYER TINTS RELIEF METHODS a)​ Each elevation zone is indicated by printing a 1.​ SPOT HEIGHTS distinctive color or tone between the bounding a)​ Indicate elevations that apply at particular points contours b)​ Location: physically documented benchmarks, b)​ Use: for small-scale map hilltops, bottoms of depressions, road intersections c)​ Assumption: elevations within a given zone all fall c)​ Use: to supplement contours within the limits established by contours d)​ Advantage: simple, very accurate for the selected d)​ Tints: (gray values) point 1.​ Lighter tones - higher elevations e)​ Disadvantage: do not give the graphic effect of 2.​ Darker tones- lower elevations shape and does not provide any indication of the e)​ Color: elevations that exist at locations between certain 1.​ Cool green - lower elevations points 2.​ Warm oranges, brown, red - higher elevations 2.​ SHADING 3.​ White - highest elevations a)​ An assumed light source from the northwest is f)​ Disadvantage: does not differentiate internal imagined as creating areas of light and shadow in a variations within each layer and has the potential for mountainous area misinterpretation b)​ Use: to show the general features where the relief 5.​ RELIEF MODEL are high and the slopes are steep; to enhance the a)​ Representation of the terrain readability of contours b)​ 3D with suitable horizontal and vertical scales c)​ Advantage: provides 3D effect c)​ A miniature of the terrain it represents d)​ Disadvantage: not quantifiable d)​ Use: for instruction, public exhibit and aid in 3.​ HACHURES special studies of geologists, geographers and a)​ Consists of rows of short, nearly parallel lines engineers whose spacing, weight and direction produce an e)​ Advantage: facilitates visual recognition of effect similar to shading terrain features; most legible of all methods b)​ Use: when relief cannot be sufficiently expressed by representing relief contours (for features like steep slopes, f)​ Disadvantage embankments and low hills in extremely flat areas) 1.​ A large amount of required space c)​ Characteristics: 2.​ Difficulty to transport 1. Thick and short on steep slopes 3.​ High production cost in both time and 2. Thin and long on flat slopes resources 3. Drawn in the direction of the slopes d)​ Advantage: provides 3D effect and represents the VERTICAL EXAGGERATION surface very well especially in areas with considerable undulation 1.​ A scale used in raised-relief maps, plans and e)​ Disadvantage: technical drawings 1.​ Exact elevations or slopes cannot be determined 2.​ To emphasize vertical features, which might be 2.​ Mass of lines conflicts with other details on the too small to identify relative to the horizontal map scale 3.​ Process is difficult and time-consuming 3.​ The ratio of vertical scale to horizontal scale  4.​ Exaggeration of 2:1 means that the mountains c)​ Most easily obtainable are twice as high as they were, if their d)​ Data redundancy in areas of uniform elevations had the same scale as the plane terrain 5.​ Normally, terrain models with a scale smaller e)​ Inability to adapt to areas of differing than 1:50,000 are exaggerated relief complexity without changing the 6.​ The smaller the scale, the more extensive is the grid size exaggeration 2.​ TRIANGULATED IRREGULAR NETWORK DIGITAL ELEVATION MODEL a)​ Vector-based representation of the ​ Digital representation of ground surface physical land surface or sea-bottom, topography or terrain made up of irregularly distributed ​ Any digital representation of the continuous nodes and lines with XYZ that are variation of relief over space arranged in a network of ​ Models containing only elevation data non-overlapping triangles ​ Almost synonymous with the digital terrain b)​ Point density increases as variations in model(DTM) height increases c)​ Flexible and fewer points need to be USES OF DEM stored than in a DEM with regularly 1.​ Extracting terrain parameters distributed points 2.​ Engineering and infrastructure designs d)​ Require visual inspection and manual 3.​ 3D display of landforms control of the network 4.​ Military purposes (weapons guidance systems and pilot training) GRIDDING METHODS 5.​ Landscape design and planning/landscape 1.​ Allows to produce accurate contour, surface, architecture wireframe, vector, image and shaded relief 6.​ Flight simulations maps from XYZ data 7.​ Creation of physical models 2.​ Interpolates the data that is dispersed on the 8.​ Line of sight analysis map area 9.​ Reduction of gravity measurements 3.​ Different gridding methods provide different 10.​ Generation of slope maps, aspect maps and interpretations of data slope profiles - preparation of shaded relief maps for geomorphological studies or DEM PRODUCTS estimation of run-off and erosion a.​ Block diagrams, profiles and horizons i. one of the most familiar forms of DTM ii. Visually appealing method of showing the 1.​ ALTITUDE MATRIX variation of the value of a quantitative variable a)​ Regular rectangular grid that is over an area obtained from quantitative iii. Overlay of several surface maps measurements from stereoscopic aerial b.​ Contour maps photographs made from analytical ​ Can easily be obtained from altitude stereoplotters matrices by reclassifying cells into the b)​ Useful for calculations of contours, appropriate height classes with slope, angles, aspects, hillshading and different colors or grey tones automatic basin delineation  ​ Also generated from TIN models by inspecting horizontal planes with the network c.​ Maps of slope, convexity, concavity and aspect ​ Slope- plane tangent to the surface as modeled in the DEM at any given point ​ Components: 1.​ Gradient - maximum rate of change of altitude 2.​ Aspect - compass direction of this maximum rate of change d.​ Shaded relief maps ​ To portray relief differences of hilly and mountainous areas ​ Requires: 1.​ Estimate of the orientation of any given surface element (slope components) 2.​ Model of how the surface element will reflect light when illuminated by a light source placed 45 degrees northwest ​ Apparent brightness depends on: 1.​ The orientation with respect to the source 2.​ The material 3.​ The slope of the model e.​ Drainage network and drainage basin delineation ​ To locate all convex downward places for streamlines and the reverse to detect ridges, drainage network, and delineate basins ​ Essential for flooding analysis and computation runoffs and landslides