Parameters of processing matrix and construction of horizontals

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Dialog of DEM processing and contouring mode contains three groups for specifying parameters:

- parameters of processing of a matrix;

- output map;

- parameters of construction of horizontals.

 

In Matrix processing options group there are:

1. Passport data control. At the established flag the check of passport data of all open matrix data onto really existing values is carried out (the minimal and maximal values, dimensions, SKO, etc.) At discrepancy of passport data they will be replaced onto really received data.

 

2. Column and row smoothing. At the established flag the smoothing of DEM for elimination of mistakes of profiling on photogrammetric devices is carried out. There are some variants to carry out the smoothing:

- first by rows, then by columns

- column first, then row

- only by rows (forward and reverse)

- only by columns (forward and reverse)

- only by rows (forward)

- only by columns (forward)

- only by rows (reverse)

- only by columns (reverse).

 

Choice of a variant of smoothing remains for the operator and is defined by type of photogrammetric device and a technique of DEM creation. Degree of DEM updating is established by means of the corresponding element located in one line with a flag of operation. The more the factor of smoothing, the greater site is exposed to the analysis and processing.

 

3. Formation of analytical structure. At the established flag the updating of a surface of a relief with purpose of receiving the more smooth forms of a relief is carried out. Degree of DEM updating is established by means of the corresponding element located in one line with a flag of operation. Processing is spent by a method of the dispersive analysis. The factor of updating defines the sizes of an elementary area for calculation of local values of a dispersion. The more the factor, the more degree of DEM updating and speed of processing is below.

During formation of analytical structure, the heights values of the matrix are modified, both on level ground and on steep slopes.      

In this case, modifying of values on the slopes leads to an "increase" in the relief, that is, the horizontals are displaced in plan, in comparison with the source matrix.

When processing the matrix, there is often a need to process the plain and mountain terrain in different ways: on plain to smooth, and on the rugged terrain to not smooth.

A complete disabling the process of  prompting of analytical structure leads to the fact that in the mountainous regions the horizontals forms correspond to the real relief, and on the plain they are not sufficiently smooth and besides, a large number of "noise" is created - small closed horizontals that do not reflect the relief forms.

When the flag «In view of local ruggedness» is set, the program automatically determines the degree of terrain ruggedness in local areas, specified by the modification coefficient. If the variance on the local area does not exceed the specified level (for example, 1 section height of relief), then the area is considered as a level ground and the heights of a relief are modified. Otherwise, the area is classified as "mountainous" and heights are not processed. The value of level can be selected for each matrix only during the research. It is better to start from a level value equal to the 1 section height of relief.

In order to force the program to set the area in which you do not need to smooth the matrix, you must first create a binary raster (black and white) and set the flag «In view of not processable zones setting by raster».  The raster name is selected in the corresponding element.

The best way to create a raster is the following method. To construct horizontals by a matrix without processing (without smoothing and prompting of analytical structure). Visually, by the received horizontals, to estimate places in which there is no need to perform smoothing. Digitize such places by areal objects (subobjects are allowed). Disable visualization of all matrices, rasters and maps, except for that one on which the areal objects are located - not processable zones, and set only objects of this type in the map view. Call the procedure for saving the map into a raster (BMP, TIF, PCX). In the procedure dialog, you must set the parameters of the raster: 1 bit per pixel and the resolution corresponding to the resolution of the source matrix. Enable the flag of using the file of binding. Then add the resulting raster to the open matrix using the file of binding. Specify the raster name in parameters of prompting of analytical structure.

 

4. Matching with elevation points is necessary for exact "stacking" of contours in region of a high-altitude point.

For adjustment the program uses all point objects having "absolute height" characteristic, or H coordinate. If point object has and coordinate Н and "absolute height" characteristic then "absolute height" characteristic will be used. Into DEM element corresponding to a point the value of a point height is entered, and surrounding elements smooth out by polynomial methods. Size of the local area, subjected processing is defined by factor of the coordination located in the same line, as a flag of operation.

 

5. DEM matching with 3D objects (XYH) is carried out for specification of values of DEM elements in region of location of three-dimensional objects. For adjustment the program uses all linear objects having three coordinates of the metrics. Check of a correctness of Н coordinate is not carried out, it is considered, that all heights are true.  Into DEM nodes to which objects with coordinate description XYH belong, or value of Н coordinate of a current point, or Н value received by a method of linear interpolation of the next points of the metrics is entered. To enlarge coordination's strip use the factor of the coordination located in the same line as a flag of operation.

 

6. DEM matching with line rivers is carried out for specification of values of DEM elements in location region of linear water-currents. For adjustment the program uses all linear objects specified by the user in dialog "Set structure of processing water-currents". For a call of dialog the Contents button, located in the same line as a flag of operation, is intended. The program forms graph of hydrography and sorts the objects by length. It is done that more lengthy objects have been processed first of all and were the initial information for the coordination of less lengthy water-currents. Heights in points of a source and a mouth are defined for the each water-current, the linear interpolation of heights with the purpose of giving monotony to decrease of H coordinate from a source to a mouth is carried out. On a trace of a water-current the DEM nodes receive values of the interpolated heights. To enlarge coordination's strip use the factor of the coordination located in the same line as a flag of operation.

 

7. DEM matching with area hydrography with a constant water level is carried out for specification of values of DEM elements in region of location of water surface with identical height (ponds, lakes, seas). For adjustment the program uses all polygon objects specified by the user in Set contents dialog.  For a call of dialog the Contents button, located in the same line as a flag of operation, is intended. For execution of operation the height is taken from "absolute height" characteristic. If it is absent, value of H coordinate of the first point of the metrics is selected. If there is no H coordinate the height is calculated by DEM.

Program calculates the centre of gravity of area object, reads out from DEM the value of height and uses it for the further coordination. To enlarge coordination's strip use the factor of the coordination located in the same line as a flag of operation.

 

In Output map parameters group there are:

1. Name of output map defines a name of a map on which created horizontals will be placed.

2. Name and code of objects. In corresponding elements the user can choose the codes of the basic, thick and additional horizontals necessary to him.

3. Output area is intended to set the sizes of a site of district on which horizontals will be created. In any case the site should be provided by matrix data. If the user has chosen a site on which DEM is not present, the program will not continue work. By default dimensions of all region of works are used for formation of horizontals, but they can be changed, using buttons: All region, Inside of frame, Inside of contour and Inside of object. At a choice of area of construction inside of a framework it is necessary to specify rectangular area of construction. At a choice of area of construction inside of a contour it is necessary to specify the any closed area, and at construction inside of object - the polygon or closed linear object.

 

In Contouring options group there are:

 

1. Flag of construction of horizontals, which is used for indication to the program of the necessity to form horizontals. This possibility allows to carry out procedures of smoothing and the coordination separately from procedures of construction of horizontals if the sizes of matrix data are great and time for processing is required significant. In this case it is possible to carry out stage by stage separate operations of smoothing and coordination, not carrying out thus formations of horizontals.

 

2. The flag of construction of additional horizontals is used in the event that it is necessary to generate also additional horizontals besides the basic and thick horizontals.

 

3. Flag for construction of bergshtrichs is used to create vector objects indicating the directions of the slopes for closed horizontals. Strokes are formed only for those closed horizontals, within which there are no other contours. In other words, only for the most "upper" or "bottom" horizontals, describing the hills and holes respectively.

 

4. Height of cross-section of relief in meters, defines a step of forming the horizontals by height in meters.

 

5. Minimum horizontal height defines the admission of a filtration for "small" horizontals. All contours which length is less than the specified value, are rejected and are not entered into an output file. However, the small contours located in region of high-altitude points are not deleted and are entered into an output file. Thus, the rule of generalization of the  contours which are not reflecting forms of a relief is realized.

 

6. Minimum and maximum height of horizontal show the real values in DEM and allow the user to be oriented in a condition of process of construction of horizontals. Except for that the parameter the minimal height can be used for the indication of the starting height for construction of contours. The height should not be less minimal and more maximal heights DEM. The program in any case will correct erroneous value during construction.

The resulting horizontal is a complex broken line, thus, some of points express the shape of the relief, but most of the points give the contour a jingle (serration). This original jingle (bounce) to the left to the right from a true axial line must be eliminated. To delete such points, methods of filtration are used.

 

7. Metric filtration factor k is a value that affects the degree of straightening of the metric sections of the obtained relief isolines.

Default value: k = 0.02; Straightening metric sections - deleting points located to the left or right of the center line at a distance greater than (k * elem), where elem is the element size (matrix step) in meters.

 

8. Delete jagging mode is used to give smooth forms to isolines of a relief by filtration methods, but taking into account the location of points on a local area.

If, within a certain local area, the metric of horizontal turns in one direction or the other one, then an image is obtained in the form of saw jagging. Tracking and straightening such areas is performed while eliminating jagging.

By combining the value of the filtration factor and the parameter of elimination of jagging, it is possible to obtain contours that have smooth shapes, while reducing the number of metric points.

In general, the procedure for filtering the contours metric is as follows. At first the double vertices in the metrics are eliminated. Then, if the flag «Filtration factor» is set the linear filtration of the vertices metric (decreasing the number of the metric's   vertices) is made. Further, taking into account a flag «Delete jagging», the «thinning out» of metrics in two passes is performed. In the first pass, vertices are filtered within the metric segments less than or equal to 2 matrix steps. On the second pass, metric segments less than or equal to 4 matrix steps are processed.

 

9. Smoothing is used for giving smooth forms to broken isolines of a relief, by addition of the metrics points by a method of interpolation of their planned position. Smoothing may be performed by various methods:

- smoothing spline (50 %) - maximum "cutting" of corners;

- smoothing spline (30 %) - average "cutting" of corners;

- smoothing spline (15 %) - minimum "cutting" of corners;

- curve Bese;

- describing spline.

 

Use different variants of smoothing for different types of terrain. For a mountainous terrain the filtration procedures are enough. For hilly terrain you can use the describing spline or a smoothing spline with minimum "cutting" of corners. For flat terrain - the curve Bese (Bézier curve) and smoothing splines.