Processing of isolines

The objects are processed which types are contained in dialog pages: Thick, Principal, Additional, Auxiliary. If the object does not contain semantics with a code specified in the dialog field Semantic code Absolute elevation the object is not processed.

During processing, the removal of isolines of small length is performed. If the removal condition (small length) is fulfilled for the isoline, then the isoline is deleted. A removal condition: The isoline length is less than dialog parameter the Minimum length. For the isolines of small length going onto a sheet border, the dialog parameter Remove isolines crossing sheet border is checked. If this parameter is not set, then the proximity of the first and last isoline points to the sheet border is checked. If the distance from the first or last point to the sheet border is less than 0.2 mm of the map, then the isoline of small length is not removed.

In case of a multisheet map, the removal of isolines of the small length extending onto a border of sheet can cause loss of isoline fragments during the subsequent uniting.

If the area of the closed isoline is less than the parameter of the dialog Minimum square, then such adjacent isoline lines of the same type are united together. The threshold for uniting the isolines of a small area is 0.4 mm of a map. If the area of result of a uniting is less than dialog parameter the Minimum square, then the isoline is removed.

Processing of thick isolines

The thick isoline can remain thickened, can be reformed to the principal one, and also can be removed depending on execution of conditions thick 1, thick 2.

Condition thick 1:

If the elevation of a processed isoline corresponds to elevation of a thick isoline of an output map the isoline type does not change - the isoline remains thick.

The isoline is thickened, if:

1)  the elevation is multiple to five Relief cross-sectional height of the output map - for scales from 1:50 000 to 1:500 000 and for scale 1:25 000 with Relief cross-sectional height of more than 2.5 meters;

2)  the elevation is multiple to ten Relief cross-sectional height of the output map - for scale 1:25 000 with the Relief cross-sectional height equal to 2.5 meters;

3)  Relief cross-sectional height is equal to 0 m either is equal to 500 m or is multiple to 1000 meters - for scale 1:1 000 000.

Condition thick 2:

If the elevation of the processed isoline corresponds to the elevation of the principal isoline of output map, then the type of the isoline changes to a new one and the thick one is converted to the principal one.

The isoline is the principal one if it is not thickened and the height is a multiple to the Relief cross-sectional height of the output map.

A new type is selected by the program from the list of the Principal dialog page, with the condition of equality of "Location" semantics values to ensure the continuity of the isoline location (on land, on glaciers, on landslides, etc.).

If the conditions thick 1 and thick 2 are not satisfied, then the isoline is removed.

Processing of principal isolines

The principal isoline can be reformed into additional one or into thickened one depending on fulfillment of conditions main 1, main 2, main 3.

Condition main 1:

If the height of a processed isoline corresponds to height of a thickened isoline of output map (see the condition thick 1), then the type of isoline changes to a new one and the principal isoline will be reformed to the thickened one. The new type is selected by the program from the list of the Thick dialog page, with the condition of equality of "Location" semantics values to ensure the continuity of the isoline location (on land, on glaciers, on landslides, etc.).

Condition main 2:

If the isoline height is multiple to the Relief cross-sectional height of the output map (Contour_Interval_Dest), then the isoline type does not change and the isoline remains the principal one.

Condition main 3:

If the isoline height is multiple to half of the Relief cross-sectional height of the output map (Contour_Interval_Dest / 2) and the Create additional dialog mode is set, then the isoline type changes to a new one and the principal isoline will be reformed to the additional one. The new type is selected by the program from the list of the Additional dialog page with a condition of equality of semantics values "Location".

If the Create additional mode is not set, the isoline is removed.

If conditions main 1, main 2, main 3 are not fulfilled, the isoline is removed.

Processing of additional isolines

If the isoline height is multiple to half of the Relief cross-sectional height of the output map (Contour_Interval_Dest / 2) and the Create additional mode is set, then the isoline type does not change and the isoline remains additional one.

If the height of an additional isoline is not multiple (Contour_Interval_Dest / 2), then the isoline is removed.

Processing of auxiliary isolines

If the isoline is auxiliary one and the Remove auxiliary dialog parameter is set, then the contour is removed.

If the Remove auxiliary parameter is not set, removal is not carried out, the isoline type does not change - the isoline remains the auxiliary one. Thus, into the protocol the message is given about presence on a map of the given auxiliary isoline for decision-making - to leave or not to leave the auxiliary isoline on the output map. Removal of auxiliary isolines can result in loss of data about heights in case of a flat plain relief.

Rarefying of obtained additional isolines

It is executed after processing of isolines at parameter value the Coefficient of density reduction, greater zero.

At the first stage of process of rarefying, a constructing the matrix of marks of the isolines superposition by output map is carried out. The matrix of marks is located in the catalog of the output map, the name of the matrix is mark_overlap.mtw. The matrix contains elements filled with a value of -19999 in those places where there is a superposition of isolines of output map, that is, two or more isolines enter the matrix element. The element size of a matrix of marks elem=k * h, where k is the coefficient of density reduction, h is the contour interval of output map.

At the second stage of the rarefaction process, the metric of additional isolines is processed. During processing, fragments of additional isolines are deleted, the segments of the metric of which are covered by the elements of the marks matrix.

The processing parameter "Save control matrix" allows you to save the matrix of overlap's marks mark_overlap.mtw in the catalog of the resulting map. Adding a matrix of marks into the resulting map allows to evaluate the correctness of the result of rarefying additional contour lines.

At removal of metrics segments the length of the resulting fragment of the additional isoline is compared with parameter the Minimum length of additional isoline. If the length of a fragment is less than the value of this parameter the fragment is removed.

The process of  density reduction of additional isolines is displayed by a separate line of progress.