Cross-Hatching in Models

There are situations where you wish to cross-hatch certain areas of a model.  There are several options which use either features or DTM triangles to generate the necessary polygonal boundaries.  The Cross-Hatch option from the DTM Tools menu will generate a pop-up menu as shown below.

When using any of the cross-hatch options, a dialog box will be displayed allowing you to specify the attributes of the cross-hatch.  Within these dialog boxes, there are some general options which are always available regardless of the type of cross-hatch that is being created.

Pen and Layer fields allow you to specify the attributes for the cross-hatch together with a Style field which allows you specify the cross-hatch pattern.  The list of available styles also allows you to specify a solid fill.  There will be a Plot Polygon check box which will allow you to plot the polygons that have been used to generate any given cross-hatch.  These polygons will use the same colour as that of the hatch and will always be solid lines.  If the solid fill has been chosen, this check button will be disabled.

Cross-Hatching Features

When hatching features, a dialog box like that shown below will be displayed.

Depending on the option chosen, one or more of the fields in the Settings group may be removed.  The Auto Close check button is available when the indicate feature is not polygonal and if set, will add the extra segment to close the feature.  If you select an open feature and this button is not checked, you must define an offset cross-hatch.

When cross-hatching features, there are two types of algorithm.  A normal cross-hatch is where the pattern completely fills the polygon calculated by n4ce.  An offset cross-hatch will generate a strip of hatch pattern around the polygons calculated by n4ce.  The Offset Hatch check box enables you to create the offset cross-hatch.  If this option is elected, the Offset field will be enabled which allows you to define the width of the cross-hatch strip.  This offset hatch is always created to the right of the indicated feature so you may need to temporarily reverse the feature to create the desired effect.  Note that the offset value should be defined in millimetres.

Normal Cross-Hatch	Offset Cross-Hatch

The Feature String option allows you to create a cross-hatch within a line feature.  You will be asked to define the hatch parameters, indicate the feature to hatch and then to indicate the origin and alignment for the cross-hatch pattern.  If the feature that has been indicated is not a closed feature, the Auto Close check box will be enabled.  If checked, this will force n4ce to create a polygon by adding a side linking the first and last points of the feature.  If it is not checked and the Offset Hatch button is checked, an offset hatch will be created to the right of the indicated feature.  If neither button is checked, nothing will happen.

The Feature String Side option allows you to create a hatch to one side of a feature.  You are asked to define the parameters in the dialog box, indicate the line feature to hatch and then indicate the origin and alignment of the hatch pattern.  When indicating the feature to hatch, you will also be asked to indicate the side on which the hatch is to be created.  The cross- hatch that is created will be a strip down whichever side is indicated using the value from the Offset field in the dialog.

The Feature Between option allows you to create a cross-hatch between two or more features.  You will be asked to define the hatch parameters, indicate the features and then indicate the origin and alignment of the cross-hatch pattern.  The bounding polygon will be calculated by taking the first line feature and joining its last point to whichever end of the next line feature is closest.  The unused end of the line will then be tested against the ends of the next feature, and so on.  Once the last feature is reached, that polygon will be closed.  You will not be able to indicate closed line features and you cannot create an offset hatch using this option.

The Feature Shape option allows you to hatch the area within a shape feature.  You will be asked to define the hatch parameters, indicate a of shape feature to hatch and then to indicate the origin and alignment for the cross-hatch pattern.

Cross-Hatching DTM Groups

The option DTM Groups allows you to hatch one or all the groups of the current DTM.  When selected, the dialog below will be displayed.  The list of groups in the current DTM is displayed to the right of the dialog.

To cross-hatch a single group, set the normal parameters to the left of the dialog, highlight the group in the list and select OK.  You will then be asked to indicate the origin and alignment for the cross-hatch pattern and the cross-hatch will be created.  In this case, the hatch will assume the colour in the Pen field.

To hatch all the groups at once, set the normal parameters to the left of the dialog, ensure that the Hatch All check box is ticked and select OK.  You will then be asked to indicate the origin and alignment for the cross-hatch patterns and a cross-hatch will be created for each group.  All the cross-hatches will use the same origin.  The colour used for the hatch associated with each group will be the same as that of the foreground colour for the group fill style.

Cross-Hatching DTM Contours

The option DTM Contours allows you to create hatches base on contour values.  The option DTM Isopachytes allows you to create cross-hatches based upon the difference in height between the current DTM and another.  When either option is selected, a dialog like the one below will be displayed.

The Settings group allows you to specify the range of heights or height differences across which a cross-hatch is to be generated.  There are three options for the Range field and these make use of the values in the Maximum and Minimum fields.

Above Maximum - A cross-hatch will be created where the DTM triangles are above the maximum value.

Between - A cross-hatch will be created where the DTM triangles are between the minimum and maximum values.

Below Minimum - A cross-hatch will be created where the DTM triangles are below the minimum value.

When generating a hatch for isopachytes, you will be asked to select the other DTM to which the current model is to be compared using the dialog box shown below.

Select the surface to which the current surface will be compared from the Second Surface list.  Two check buttons allow you to take further information into account.  The Group Depths check button allows you to take account of the depths applied to DTM groups in the current model.  In this case, the isopachyte value will be reduced by the depth assigned to the groups of which a DTM triangle is part.  The Double Depths check box allows you to consider the group depths in both the current model and that to which it is being compared.

Cross-Hatching Cut and Fill

The option DTM Cut & Fill allows you to create a hatch showing where there is cut and fill when the current model is compared to a second.

When defining the parameters for the hatches, you should define two hatch colours, one for the cut hatch and one for the fill.  The same layer and hatch style will be used for both cross-hatches and you will only need to indicate one hatch pattern origin and alignment.

The Swap Cut & Fill check button allows you to swap the cut and fill when doing the surface comparison.  This allows you to work from either the design to the OGL or vice versa.  If you are working on the OGL and comparing to the design surface, you will not need to check the Swap Cut & Fill button.  The buttons to take account of the depths assigned to groups have already been described in the previous section.

After setting the parameters, you will be asked to select the DTM to which the comparison is to take place and then the origin for the hatch patterns.

Deleting Cross-Hatches

The option Edit Delete allows you to delete any cross-hatches that you have created.  You will be asked to indicate a cross-hatch and to do this, you should ensure that you indicate an element within the cross-hatch.  This option will also delete other hatches that have been created using CAD tools in the dedicated CAD backcloth.  Note that this option will only delete the cross-hatch and not any polygon created at the same time as the hatch.