Contours are lines of a constant height and are generated automatically when a DTM is created in n4ce.  There are two types of contours in n4ce.  

Here's a video to help:

• Quick Draw:  These appear as soon as a DTM is added to the model. They change in real-time as the DTM is manipulated or otherwise changed. If a point has its height changed, or a triangle is deleted. The contours will update to reflect the change.  Where a height is altered, more or less contours will be added as needed.  If a triangle is deleted, then the contours that went with it will also be removed. Quick draw contours can be turned on or off via the Contours tick box in the Layer Override dialog (ALT+F9). If a Model is exported with quick draw contours turned on, then each triangle's contours are output as single short straight lines.  
  
  
• Threaded: These are final presentation quality contours that can be curved and broken to have level text inserted into them.  They are generally created once the DTM has been fully edited as they do not update if the DTM is changed.  Threaded contours are continuous polylines that thread through all of the triangles so that when exported they are no longer a series of broken line segments.  Whereas quick draw contours are enabled under the Contours option in the layer override dialog.  Threaded contours are plotted in the CAD backcloth of a Model.  They are therefore tuned on or off by ticking or un-ticking the CAD option in the Layer Override dialog. They can also be edited by entering the CAD backcloth of a model.

Settings

To configure the display of contours quick or threaded, select the Settings option from the Contours Menu.

There are 6 primary sections to the contours dialog.

Intervals

By default, there are two contour intervals added to the model.  These could be thought of as Major/Highlight and Minor/Normal. There must be at least one contour interval, so the Normal interval can not be removed.  However, once any changes are Saved, these will become the permanent settings so the contours do not have to be reconfigured each time.

Maximum Loop: When creating thread contours, you now have the option to ignore loop contours less than a user-defined length.

Lines

This section starts by defining the layer, pen, and linestyle used for the currently selected interval. Note that each interval can, and does have its own settings.

Curve Threads

This applies when creating Threaded Contours.  With this option enabled the CAD contours that are generated are curve fitted rather than just being straight. When this is enabled the curve chord length field becomes active.  This defines a value, with which smooth curves will be generated. Larger values will result in angular style curves which draw fast. However, smaller values give much smoother curves but can take longer to generate as a result.

The Filter Offset value is used to help stop really small curves from being formed.  If its value is above 0, then the curve will only be drawn if that curve's offset to the straight line that it's replacing, is larger than that value.

Straight Contours

Curved Contours

Break On Lines

With this option enabled, curved threaded contours are broken and started again if they cross a feature that is also a breakline in the DTM. This creates more accurate contours that correctly follow sharp changes in level.

Override Quick

This option will automatically turn off the quick draw contours once Threaded Contours are generated.  This saves the user from having to do it afterwards via the Layer Override dialog.

Shading Colours

Enabling this option uses the height shading colours to render the contours rather than the colours specified in the settings dialog. Height shading is controlled via the DTM Settings option under the Settings menu in a Model. Triangle Shading can also be made visible by activating it in the Layer Override dialog.

Group Depths

If a model has been grouped up, and those groups have been assigned a depth.  With this option enabled the contours will take any group's depth into account. This is usually used to show formation level contours rather than a finished surface.

Filter Along

This option combined with the filter offset value, runs a Douglas-Peucker line simplification routine along the resulting threaded contours.  This is to try and minimise the number of nodes along the contour lines, while still keeping their overall shape.  The default value of 0.1m will keep any nodes that deviate by that value or more from a line drawn between the node before and after.  Over large models, this can help reduce the complexity of the polyline nodes on complex earthworks models.

Interval

Each contour is assigned a height interval to draw at. The Normal interval must be the smallest value for the contours to be drawn correctly and not double up where multiple intervals of different contours overlap.

where applicable contours can also be drawn within predefined minimum and maximum values.  This allows cut and fill contours for instance on an isopachyte model to be drawn in different colours.

Annotation

Style

This defines the text style used to annotate threaded contours.

Text Offset

Defines the distance from the contour line in mm, that the height annotation is placed.  If this value is set to zero the text will appear in the middle of the line.  However, if the annotation is being applied to threaded contours, then the CAD polyline representing the contour line is gaped to allow the text to fit neatly within it.

Decimal Places

Sets the number of decimal places to be used to annotate the current contour interval.

Always Readable

Applies a function to the CAD text, so that no matter whichever way it is facing, n4ce will render the text so that it can be read.  If the text were to be rotated by 180 degrees, n4ce will automatically flip it so that it can be read clearly.

Above contour

Places annotation that has a text offset greater than zero, above the contour in the uphill direction.

Quick Annotate

This option labels the current quick draw contours by striking a pick line through them.  Note that quick draw contours can not be gaped to insert level annotation.  Only Threaded contours can be annotated in this way.

Threads

Create

This option displays the same settings dialog as discussed at the start of this article.  However, when OK is pressed, the threaded CAD contours will be added to the model.

Single

Use this function to generate a single threaded CAD contour at a given level.  This is sometimes used to plot a flood level at a precise datum.

Smooth

This post processes the threaded contours via the Douglas-Peucker algorithm to try and remove redundant polyline nodes.  See the help on the Filter Along option above for more information.

Delete

Clears the model of all threaded contours and any associated annotation.

Annotate

Indicate

Annotates an indicated threaded contour at a specified location.

Strike Like

Annotates all threaded contours that are crossed by a given strike line.  Having selected this option, click and release the mouse cursor.  A rubber band line will be drawn and attached to the initial position.  Click again when this line crosses the threaded contours in a location suitable to be annotated.

Distance

Annotates all Threaded contours at regular intervals.  Whilst this annotates all contours, the annotation will not necessarily line up because all the contours have a different start position and length.

Ends

Annotates all threaded contours that are NOT closed, at their ends.

Delete

Delete

Removes a single item of contour annotation.

All

Deletes all contour annotation and heals the gaps if there are any.

Reset

Sets all the contour annotations to use the current text defaults in the contour settings dialog.

Flip

Mirrors a selected item of annotation to the opposite side of its contour line.