First section an overview of large-scale topographic mapping
First, large-scale topographic mapping of the concept of
The main day of the Ordnance Survey is to obtain a variety of different scales of topographic maps. Current 1:1 million scale topographic maps -1:5 10000 multi-purpose aerial survey method, less than 1:1:5 10000 scale topographic map is based on a larger scale topographic maps and all kinds of information made downsizing. Thus, commonly referred to as large-scale mapping, multi-fingered 1:500-1:50 m-scale mapping. Human-scale topographic mapping is a control point for the station, using measuring instruments and tools, and mapping out its surrounding surface features, topography feature points, and using an overhead projector is the method, according to the provisions of topographic map style symbols, according to a certain The scale drawings painted in the process. Here surface features, topography of the feature points, collectively referred to as the Ministry of points broken. Therefore, topographic mapping, also known as the Department of Measurement broken.
Large-scale topographic mapping on a full variety of basic measurements and a variety of comprehensive application of basic measuring instruments, is an integrated plane and elevation measurements.
Large-scale mapping of the features are: a small test area, large scale, high accuracy requirements.
Second, large-scale topographic mapping of the basic requirements
Large-scale topographic maps to be issued in accordance with national unity, "Ordnance Survey standard" in testing facilities, topographical map of the surface features and the feature contours of national unity must be established "topographic map-style" spy set notation, landscape use, etc. high-speed wire in conjunction with other landscapes to represent symbols and Notes. The accuracy of large-scale topographic maps must meet certain requirements, which in the "Ordnance Survey norms" There are clearly defined.
Mapping of topographic maps should be clear and easy to read, surface features, landscape representation and symbols used, should be properly consistent; various elements to be surveying and mapping is complete, the contents of a comprehensive trade-offs should be appropriate and to focus on the purpose of display and mapping the corresponding surface features, geomorphological features; map surface finishing to be beautiful, and in accordance with the provisions of schemata.
Third, large-scale topographic maps from the choice of the basic contour
Contour line represents the topography of the accuracy and level of detail and contour mapping from the size and scale are closely related. A certain scale, contour intervals of the smaller, the map-ping between adjacent contour lines is also smaller distance that the landscape out of the more detailed, more real; the contrary, the contour can not be too much detail from the reflected landscape. However, if the contour distance is too small, big, slope, contour lines will appear too dense, resulting in surface is not clear, but affect the landscape representation. Therefore, the choice of contour distance by scale, ground slope and elevation accuracy constraints.



Fourth, large-scale topographic mapping of the basic procedures for
Carrying out large-scale topographic mapping should be carried out in accordance with certain procedures, namely: the collection of information and the preliminary field reconnaissance, based on the control points laid to carry out basic control test area measurements; for mapping a series of pre - preparatory work in order to ensure the smooth progress of the work of surveying and mapping; in test site density is not enough when you want to encrypt the test site;-by-station to complete pieces of work the Department of Surveying and Mapping; to access Edges mapping and field access map; complete inspection apricot, acceptance wild Original finishing such as topographic mapping of the end of the work.
Section II pre-prepared mapping T to
The traditional mapping method before mapping, in addition to good equipment, tools and related data, data preparation work, should be carefully prepared mapping board. It includes the preparation of drawings, drawing and plotting grid coordinates of control points and so on.
First, preparation of drawings
Generally use the thickness of 0.07-0.1mm, after sanding the surface of polyester film. Polyester film has good transparency, scalability is small, not afraid of humidity, strong and durable, etc., can be water washed to keep the surface clean, and may dwell directly on the base map on a blueprint for re-drying. But the polyester film are flammable, easy to fold and aging such shortcomings, it is in the surveying and mapping, use and storage of fire prevention should be the process of folding.
Mapping using the polyester film, just a transparent adhesive tape it can be fixed in the surveying and mapping board mapping.
Second, draw the coordinate grid
By plotting coordinates of control points in the drawings will serve as a basis for measuring the Department of broken, graves show points directly affects the accuracy of mapping quality. To this end, we must first accurately draw power grid coordinates.
Mapping dedicated polyester film, are usually printed with standardized, accurate grid coordinates, without drawing on their own. If the polyester film on the non-coordinate grid, or use ordinary drawing paper for mapping, you can use grid coordinates instrument or coordinate ruler tool to draw special instruments such as grid coordinates. If no such special equipment, you can draw the following diagonal method.
Is to draw the 50cmx 50cm grid coordinates to illustrate grid coordinates of the rendering method.
As shown in Figure 8-2-1, first in the drawings, draw two diagonal, with its intersection of M as the center and take the appropriate length of the radius draw arc, cross-diagonal in A, B, C, D point , with a straight line connecting adjacent points were rectangle ABCD; respectively from A, D along AB and DC played two directions at intervals of 10cm set point, set a total of 5 points; again from A, B are two points along the AD and BC respectively with effect direction at intervals of 10cm set point, the same set 5:00; connected to the edge of the corresponding points, or get 50cmx 50cm of the grid.
Coordinate grid, after a good painting should immediately check with a ruler grid of intersections are in the same - a straight line, shown in Figure 8-2-1 in the ab-line, the deviation should not exceed 0,2 mm, while Fig profile of the Angle line length difference with the theoretical length of not more than 0.3mm. If the difference exceeds allowed value, and should be modified or redraw grid.
Drawing grid network due to the higher accuracy requirements, so the line should be very thin (0.1mm), and used 3H into 4H pencil drawing. Grid rendering is completed, should be wiped auxiliary lines.