Horizon processing

During processing, some horizontals may be deleted or transformed into horizontals of another type. The types of processed horizontals are contained in the tabs of the dialog: "Thickened", "Main", "Additional", "Auxiliary". When processing horizontals, the height value is requested from the semantics, the code of which is specified by the parameter of the dialog "Code of Absolute Height Semantics".

When deleting short and small area horizontals, parameters specified in the group "Contour Line Deletion Conditions" are used: "Minimum Length", "Minimum Area", "Delete Contour Lines on Sheet Frame". When transforming the type of horizontals, continuity of the horizontal location (on land, glaciers, landslides, etc.) is ensured.

The metric of the obtained horizontals can be smoothed. To do this, when setting parameters, you should specify the "Smoothing Coefficient" (a number greater than 0 and less than 1, recommended value 0.5). When the coefficient value is zero, metric smoothing is not performed. During processing, contour lines that do not belong to any sheet horizontal are removed. Such contour lines remain on the map after horizontal deletion. The types of processed contour lines are contained in the dialog tab "Contour Lines". The parameter of the dialog "Minimum Distance from Contour Line to Contour Line" is used to determine ownership.

During processing, labels of horizontals that do not belong to any sheet horizontal are removed. Such labels remain on the map after horizontal deletion. The types of processed labels are contained in the dialog tab "Contour Labels". The parameter of the dialog "Minimum Distance from Contour Line to Label" is used to determine ownership. If the processing parameters include the mode "Create Additional", then the resulting additional horizontals obtained during processing can be thinned out, meaning a reduction in the density of additional horizontals. To reduce the density of additional horizontals, when setting parameters, you should specify the "Density Reduction Coefficient" (a number greater than 0 and less than 10, recommended value 2). When the coefficient value is zero, density reduction is not performed. During thinning out, the length of an additional horizontal may decrease. If the resulting length is less than the parameter "Minimum Length of Additional Contour Line", then the additional horizontal is deleted. The process of reducing the density of additional horizontals is displayed with a separate progress bar.

If the length of a horizontal is less than the threshold length value (in the field "Minimum Length") or the area of a closed horizontal is less than the threshold area value (in the field "Minimum Area"), then the horizontal is deleted. If the absolute height of a horizontal is not a multiple of half the height of the derivative map section (additional horizontal of the original map), then the horizontal is deleted.

If the absolute height of a horizontal is a multiple of half the height of the derivative map section and the mode "Create Additional Horizontals" is specified in the dialog, then the horizontal is transformed into an additional one. If this mode is not specified, then the horizontal is deleted. When specifying a density reduction coefficient greater than zero, automatic deletion of additional horizontals in mountainous terrain occurs. A special height matrix is used for thinning out additional horizontals. The creation of the matrix is done automatically. Parameters for constructing the height matrix are contained in the IMH file (see Appendix 5). The IMH file is created and filled manually using Notepad (Windows). The file name must correspond to the name of the digital classifier (classifier 100t18g.rsc corresponds to file 100t18g.imh).

Note: In case the IMH file is missing in the directory c:  thinning out of additional horizontals will not be performed.

Thickened horizontal may remain thickened, be transformed into a main one, or be deleted depending on the fulfillment of conditions thick1, thick2.

Condition thick1: If the height of the processed horizontal matches the height of the derivative map's thickened horizontal, the type of the horizontal remains unchanged - it stays thickened. A horizontal is considered thickened if: 1) the height is a multiple of five relief sections of the derivative map - for scales from 1:50,000 to 1:500,000 and for 1:25,000 scale with relief section height greater than 2.5 meters; 2) the height is a multiple of ten relief sections of the derivative map - for 1:25,000 scale with a relief section height of 2.5 meters; 3) the height is either 0 meters, 500 meters, or a multiple of 1000 meters - for 1:1,000,000 scale.

Condition thick2: If the height of the processed horizontal matches the height of the derivative map's main horizontal, the type of the horizontal changes to a new one, and the thickened horizontal transforms into a main one. A horizontal is considered main if it is not thickened and the height is a multiple of the relief section of the derivative map.

The new type is selected by the program from the "Main" dialog tab with the condition of equal values of the "Location" semantics to ensure continuity of the horizontal location (on land, glaciers, landslides, etc.). If conditions thick1 and thick2 are not met, the horizontal is deleted.

The main horizontal can be transformed into an additional or thickened one depending on the fulfillment of conditions main1, main2, main3.

Condition main1: If the height of the processed horizontal matches the height of the derivative map's thickened horizontal (see condition thick1), the type of the horizontal changes to a new one, and the main one transforms into a thickened one. The new type is selected by the program from the "Thickened" dialog tab with the condition of equal values of the "Location" semantics.

Condition main2: If the height of the horizontal is a multiple of the relief section of the derivative map (Contour_Interval_Dest), the type of the horizontal remains unchanged, and it stays as a main one.

Condition main3: If the height of the horizontal is a multiple of half the relief section of the derivative map (Contour_Interval_Dest / 2) and the "Create Additional" dialog mode is set, then the type of the horizontal changes to a new one, and the main one transforms into an additional one. The new type is selected by the program from the "Additional" dialog tab with the condition of equal values of the "Location" semantics. If the "Create Additional" mode is not set, then the horizontal is deleted.

If conditions main1, main2, main3 are not met, the horizontal is deleted.

If the height of the horizontal is a multiple of half the relief section of the derivative map (Contour_Interval_Dest / 2) and the "Create Additional" mode is set, then the type of the horizontal remains unchanged, and it stays as an additional one. If the height of an additional horizontal is not a multiple of (Contour_Interval_Dest / 2), then the horizontal is deleted.

If a horizontal is considered auxiliary and the "Delete Auxiliary" dialog parameter is set, then the horizontal is deleted. If the "Delete Auxiliary" parameter is not set, deletion does not occur, and the type of horizontal remains unchanged - it stays auxiliary. In this case, a message is issued in the log about the presence of this auxiliary horizontal on the map for decision-making - whether to keep or remove it on the derivative map. Deleting auxiliary horizontals may lead to loss of height data in case of flat plain relief.

Thinning out of obtained additional horizontals is performed after processing horizontals with a value greater than zero for the "Density Reduction Coefficient" parameter.

In the first stage of the thinning process, a matrix of overlap labels for horizontals is constructed based on the derivative map. The overlap label matrix is located in the derivative map directory and is named mark_overlap.mtw. The matrix contains elements filled with a value of -19999 in areas where horizontals of the derivative map overlap, meaning where two or more horizontals coincide. The size of each label matrix element is elem = k * h, where k is the density reduction coefficient and h is the height of the derivative map section.

In the second stage of the thinning process, additional horizontals are processed. During processing, segments of additional horizontals are removed if their metric segments are covered by elements in the overlap label matrix. When removing metric segments, the length of the resulting fragment of the additional horizontal is compared with the "Minimum length of additional contour" parameter. If the fragment's length is less than this parameter, the fragment is deleted.

The process of reducing the density of additional horizontals is visualized by a separate progress bar.