Building terrain analysis

This part is previously written some of the content on terrain analysis, but also part of the information collated from the Internet.

Topographic analysis

Topographic analysis is an important part of urban planning, and is one of the basic analyses of urban planning. Topography and geomorphology analysis has been widely used in different periods and depths of urban planning, from the macro-scale urban site selection, urban layout, functional area organization to the micro-scale road network, landscape organization, none of them are not affected by topography and geomorphology, therefore, topography and geomorphology analysis is ubiquitous to the impact of urban planning.

For a long time, the basic data of urban planning is usually the plane topographic map data, on which simple terrain analysis can be carried out. In recent years, with the development of information technology, especially GIS technology, a variety of new methods and application models are constantly integrated into the field of urban planning, the traditional terrain analysis from two-dimensional plane analysis to the development of a new three-dimensional terrain analysis and three-dimensional perspective, thus helping planners to carry out terrain analysis based on terrain characteristics. It helps planners to carry out rational and scientific urban planning according to the terrain characteristics.

The basis of terrain analysis is the establishment of a digital elevation model (DEM), which is mainly used to describe the undulation of the ground, and can be used to extract a variety of terrain parameters, such as slope, slope direction, etc., and to carry out through-view analysis and other applied analysis. At present, DEM is mainly established from: ① contour lines in topographic maps; ② extraction of elevation data through remote sensing images; ③ other ways, such as global positioning system (GPS) and laser scanning altimetry system.

The DEM consists of two expression forms: regular grid (GRID) and triangular grid (TIN). In addition, the contour map based on the two-dimensional planar form can also be understood as another way of expression of the digital messaging. GRID is a set of the same size of the grid to describe the terrain surface, which can fully express the details of the elevation changes, topological relationships are simple, but for the expression of the irregular ground features is slightly incongruous. TIN is composed of a series of non-intersecting triangles formed by dispersed terrain points according to certain rules, which is in harmony with the irregular ground features and can express the slender functional features and superimposed arbitrary shaped area boundaries.GRID commonly used generation algorithms include inverse distance power interpolation, trend surface interpolation, spline interpolation, Kriging interpolation, etc.; TIN generation algorithms mainly include the segmentation 2 subsumption method, the insertion of the method point by point, and the gradual growth method.

The essence of terrain analysis in urban planning is to broaden and extend the application scope of DEM. From the perspective of the complexity of terrain analysis, terrain analysis can be divided into two categories: one is the calculation of basic terrain factors (including slope, slope direction, etc.); the other is the derivation of other terrain analysis, including terrain quantitative calculation, access analysis, terrain feature extraction, etc. These analyses are carried out through the DEM. These analyses are realized through the calculation and analysis of DEM data.

1, basic terrain analysis

The basic terrain analysis often used in urban planning are: elevation analysis, slope analysis, slope direction analysis, which cover the three basic elements of terrain: elevation, slope and slope direction. Among them, slope is defined as the tangent between the horizontal plane and the local ground surface, which contains two components: slope - the ratio of the maximum value of the change in elevation (often referred to as gradient); and slope direction - the direction of the maximum value of the change ratio. The more common measures are: slope is measured as a percentage and slope direction is measured as an angle from due north.

Basic terrain analysis can be used to assist in delineating urban layouts and building patterns. For example, a slope of not less than 0.3° is required on flat land to facilitate the exclusion and convergence of surface water. It can also be used from the perspective of construction engineering to classify urban land into different types according to the degree of appropriateness for urban construction: one type of land, i.e., suitable for construction, with a terrain slope of less than 10°; two types of land, i.e., land that is basically suitable for construction (with terrain slopes of 10-20°); three types of land, i.e., unsuitable for construction; and three types of land, i.e., land that is not suitable for construction (with terrain slopes of less than 10°). Class II sites, i.e., sites that are basically buildable (topographic slope of 10-20°); Class III sites, i.e., sites that are not suitable for construction, with a topographic slope greater than 20°. This is a classification of the suitability of building sites from the perspective of pure slope, but the actual situation is much more complex, taking into account a variety of factors. In addition, the slope of the road is also important for the selection of routes, urban facilities have different requirements for the slope of the land, the slope of the surface affects the use of land and building layout.

Basic terrain analysis can be used in the study of natural ecological landscape and other fields to assist the special planning. For example, agricultural planning in mountainous areas, etc., need to focus on the influence of topographic factors, the three elements of basic terrain elevation, slope and slope direction through the redistribution of the three basic environmental elements of light, water and heat to affect the conditions of agricultural production. In particular, elevation determines the amount of solar radiation received by the area and the corresponding energy lost to thermal radiation, causing a gradual change in local temperature and moisture conditions, and creating local microclimatic conditions. Precipitation conditions in a region are closely related to the direction of the slope. Differences in slope conditions control the intensity of soil erosion. If the slope is gentle, the land has a high water-holding capacity and is less prone to erosion, making it suitable for farming activities, while on the other hand, it is only suitable for forestry. Therefore, different topographic features influence the conditions of agricultural production and the choice of land use. Another example, such as according to the national policy of returning farmland to forests, active management of existing sloping arable land, more than 25 degrees of sloping arable land in the implementation of the planned return of farmland to forests and grasses, not only is conducive to environmental protection of the central and western, but also the adjustment of the agricultural structure, improve the income of the farmers have a positive significance, which also needs to carry out the basic terrain analysis.

The following are the criteria for categorizing the suitability of urban land based on topography and other elements:

The evaluation of the suitability of urban land can generally be divided into three categories (sometimes also divided into four or five categories):

( 1) A category of land. That is, suitable for the construction of the land, topographic slope of 10% or less; soil foundation bearing capacity of more than 15 tons / square meter; groundwater level is lower than the foundation of the building, the general depth of 1.5 ~ 2 meters; has not been inundated by floods; no swamps; no gullies, landslides, landslides, karst, and so on.

( 2) the second category of land. That is, the basic can be built on the land, between a class and three types of land; foundation bearing capacity of 10 to 15 tons / square meter, topographic slope of 10% to 25%, the depth of the groundwater table is 1 to 1.5 meters.

( 3) Three types of land. That is, the land is not suitable for construction, the foundation bearing capacity is less than 10 tons / square meter, the peat layer or quicksand layer is more than 2 meters; terrain slope is more than 25%; flood inundation is often more than 1 ~ 1.5 meters; there is a ditch, landslides; occupying productive land; the depth of the groundwater table is less than 1 meter.

The following table shows the effects of different sea waves on vegetation and climate:

2. Extended terrain analysis

At present, most of the practical applications of terrain analysis still remain at the level of data, most of which are limited to simple visualization and demonstration, with little in-depth quantitative analysis, and basically ignoring the mining of the data itself or information extraction, thus making it difficult to achieve high data application benefits. Therefore, it is difficult to realize higher benefits of data application and value-addedness of spatial data. Therefore, in order to realize more effective utilization of spatial data and thus promote its depth and breadth, value-added application of spatial data is the key. From the application level, spatial topographic data are no longer just some abstract points, lines, surfaces, etc., nor are they just maps with different expressions and scales, but geographic phenomena and parameters with spatial coordinates and spatial relationships, and the interpretation and expression of these phenomena and parameters are precisely the most urgently needed information in most practical applications. Therefore, the future trend of terrain analysis is to extract the terrain parameters and terrain feature information that are urgently needed in practical applications from pure digital elevation data, and apply them to various fields, which is the extended terrain analysis.

Extended terrain analysis mainly includes terrain calculation, earthwork analysis, terrain profile analysis, through view analysis, light analysis, watershed network and terrain characteristics, tidal inundation analysis, sea and land change analysis, etc., which can produce different thematic maps and serve as the reference basis for background analysis and decision-making in urban planning.

Topographic calculation mainly includes the calculation of elevation of any point on the surface of the terrain, the calculation of regional average elevation, the calculation of horizontal distance, the calculation of surface distance, the calculation of regional area, the calculation of regional excavation and filling volume, etc., which is an important content of topographic analysis, and its application is very wide, and it is necessary to carry out the calculation of topography for the application of details of the terrain involved in each special planning. Soil volume analysis in engineering (such as in the highway, railroad, pipeline, etc. design process) is widely used, often need to calculate the amount of fill and excavation of the project and the production of profiles, which is based on the terrain model, measuring the difference in volume between the two surfaces, that is, the volume calculation. In practical application, in order to achieve the best construction efficiency, in the engineering design, minimize the distance of the excavation and filling of the earth transport is an important indicator of efficiency, in each given local area, using the difference between the design elevation and the actual ground elevation, calculating the amount of excavation and filling of the earth volume required by the project, and then using the spatial combination of the optimization to derive the best construction program, in order to achieve the balance of excavation and filling of the earth with the least amount of handling. Earthwork cut and fill analysis and program optimization is one of the earliest application areas of digital terrain analysis, and its application scope includes various special planning such as estimating the amount of earthwork for roads, ditches, pipelines, transmission and distribution lines, etc., and planning and designing of land remediation projects and land reclamation projects.

Passage analysis, as one of the important elements of terrain analysis, has a wide range of application background. A typical example is the setting of a landscape element, which should be located so that it can see an area of interest and the line of sight cannot be blocked by the terrain. This is a typical point-to-area view problem in view-through analysis. Similar problems are also used in special planning, such as the setting of wireless transmission towers in communications. The visualization problem can be divided into point visualization, line visualization and surface visualization. The point of access refers to the visibility problem between the calculated viewpoint and the point to be determined; the line of access refers to the known viewpoint, the calculated viewpoint of the field of view; the regional access refers to the known viewpoint, the calculated viewpoint can be visualized on the surface of the terrain surface of the collection of problems. In landscape planning, the application of through-view analysis is more extensive, in landscape planning, through-view analysis is often called visual field analysis, in the landscape, tourism planning and design, can be used in the selection and arrangement of attractions, residential and tourism development zones, the location of the site, the evaluation of attractions along the highway or river, and so on. For example, in the coastal area through the visual field analysis to evaluate the seascape effect of each area, to find the seascape area with the widest visual field, that is, the area with the best seascape.

Light analysis is an extension of terrain analysis, which has more applications in urban planning. Setting parameters such as the sun's altitude angle, sunshine analysis. It is widely used in real estate.

The extraction of geomorphological features of the watershed and the automatic segmentation of the watershed topography, which is the basic technology for spatial simulation of the watershed. Based on the grid DEM automatic extraction of basin features and automatic terrain segmentation technology mainly includes two aspects: 1) basin geomorphology structure definition, definition of features that can reflect the structure of the basin, the establishment of grid DEM corresponding to the micro-geomorphic features. 2) automatic extraction of features and automatic terrain segmentation algorithms. The grid DEM data are some discrete elevation point data, and each data itself cannot reflect the complexity of the actual surface. In order to get the morphologic structure of watershed landforms from the grid DEM data, it is necessary to adopt a clear structural model of watershed landforms, and then design the automatic extraction algorithm for this structural model. Definition and extraction of characteristic landforms: According to the relationship between the elevation of grid points and the surrounding elevation values, the grid points are divided into several categories such as slopes, depressions, watersheds, valleys, terraces and saddles. The elevation difference between the center point and the eight neighboring points is calculated first, and then the elevation difference is sorted, and then a feature code is assigned to the center point grid according to the characteristics of the elevation difference sequence. Then the grid points are classified into known characteristic geomorphic categories by combining features of a series of feature codes using pattern recognition. Ridgeline and valley line extraction: Automatic detection of ridgelines and valley lines is actually an automatic search for concave and convex points. The simpler operator is the 2*2 local operator. The operator is slid over the DEM data, comparing the elevation of each grid point with the elevations of neighboring grid points in the rows and columns, and marking the grid point with the smallest elevation (for valley line detection) or the largest elevation (for ridge line detection). After calculating the entire DEM data, the remaining unlabeled grid points are those on the ridgelines or valley lines.

In addition, terrain analysis is also the basis for three-dimensional terrain simulation, three-dimensional digital terrain model and remote sensing images and other graphic image information, can fully reflect the spatial structure of the project and the environment and the nature of the characteristics of the city planning to improve the efficiency of the quality of urban planning and the expression of an important role in the display of the terrain and animation output of the main method.

In short, terrain analysis is an important part of urban planning.