Editing the Terrain – Contour Edits

Workspaces let you change the terrain model and observe the effects on the analyses. This section discusses the powerful contour-based editing tools. For an overview of the process please consult the introduction page.

Contours are curves with a given elevation. They can be closed curves (for instance when modeling a basin or a hill), open curves (when modifying only part of a hillside), or even points (to specify the elevation at a single location only). SCALGO Live automatically interpolates the terrain elevation based on your contours.

Unlike the features created with the traditional tools, contours work in combination. A group of contours that together modifies your terrain is called a contour group in SCALGO Live. While creating or editing a contour, the contour group that it belongs to is indicated with a dashed yellow outline.

By their very nature, contours do not touch or intersect each other. SCALGO Live enforces this condition for contours in the same contour group.

You can create contours using the five contour tools in the Contours section of the workspace edit panel. The first four tools allow you to create or import contours, while the last tool enables you to extract contours directly from the terrain model.

Closed contour at a fixed elevation. Use this tool to model a basin or a hill that lies entirely inside your workspace. In "automatic mode", the elevation of the contour is taken from the terrain at the first point you click during drawing. Alternatively, you can specify the desired elevation before drawing the curve. (In either case you can later modify the elevation using the select tool.)

Note that when automatically picking the elevation, it is taken from the current terrain, that is, including all the terrain edits you have already made. A good strategy to use the automatic elevation assignment is therefore to create contour groups inside-out, that is, starting with the innermost contours.

A point contour simply specifies an elevation in a single location. They are typically used to mark extrema inside the innermost closed contours, but can also help to make sure your design meets certain given elevation constraints.

You can also create point contours outside any existing contour group. In this case, SCALGO Live automatically creates a new contour group that interpolates the elevation between the existing terrain and the new point constraint. You can edit the boundary of this contour group to meet your design.

Once you add more than one point contour to a contour group, the interpolation is entirely based on your points (the terrain elevation is no longer used). You can quickly sketch a design by adding points at the extrema and refining with additional points until you are satisfied with the result.

An open contour specifies a fixed constant elevation along a path. They are used much like point contours. If you draw an open contour outside your existing contour groups, SCALGO Live automatically creates a boundary and interpolates between the terrain and the path elevation. Once there is more than one contour inside the contour group, interpolation is only based on the contour elevations.

When you want to model a hill side without having to model the entire hill, you want to draw only those parts of the hill's contours that are of interest to you. SCALGO Live makes this possible through dividing contours. These are open contours that start and end on the boundary of the contour group, and therefore divide the area of the contour group into individual regions. Within each region SCALGO Live interpolates between the neighboring dividing contours.

The fifth contour tool is meant for extracting contours from the workspace terrain model. After you draw a polygonal boundary for your new contour group, SCALGO Live extracts lines at the chosen elevation interval from the current terrain (that is, with all your other modifications applied). You can then add, delete, and modify contours to modify the terrain.

Instead of drawing a boundary, you can also drag a vector file (GeoJSON, GeoPackage, Shapefile, Tab) with a single polygon into this tool.

You can import contours from a vector file, please consult the section on importing workspace edits for details..

To avoid a sharp edge (vertical wall) at the outer boundary of your contour group, you can add a blending area to the contour group. Inside the blending area, SCALGO Live interpolates between the elevation of the existing terrain and the contour group, leading to a smooth transition.

To create a blending area, select any contour line of the contour group in the Select tool. Then right-click on the yellow dashed outline of the contour group and select a distance for creating the blending area. Once it has been created, you can edit the outline of the blending area like any other feature.

Often you may want to operate on all the contours that form some object in your design at once. A few such operations are provided by the yellow dashed outline that is shown around your selected contour group.

You can move (translate) the entire contour group by holding the Shift-key and then dragging the yellow dashed line.

You can delete an entire contour group from the right-click menu of the yellow dashed line.

Finally, you can export all the contours of a contour group from the same right-click menu.

It is often helpful to be able to see contour lines of the current terrain. While in any of the contour drawing tools (the first four contour tools), you can right-click anywhere in your workspace and ask for a contour line at this and nearby elevations.

SCALGO Live will show the resulting contour line as a thin blue line, an auxiliary contour. You can create arbitrarily many such auxiliary contours, clear them individually (by right-clicking on it) or all at once (right-click anywhere).

When you draw a contour in SCALGO Live, you will be drawing a smooth curve, because in natural terrains contour lines do not normally have sharp turns. When importing polygonal features from external software, on the other hand, SCALGO Live honors the imported geometry and creates polygonal contours. You can convert between the two representations using the right-click menu on the contour line (Convert to polygon and Convert to smooth curve). The conversion will fail if it would create a curve that intersects other contours of the contour group - in this case you may have to modify the curve first, delete some of its points, etc.

It could sometimes be useful to work with contour groups that overlap each other. For instance, you might first have modeled a basin using contours, then modified the basin using simple edit features, and then traced the resulting terrain model to obtain new contours that you can edit again.

SCALGO Live permits contour groups to overlap (while the contours inside a single contour group must never touch or intersect). To draw a new contour group on top of an existing one, you cannot use the contour tools normally - SCALGO Live would automatically add the new contour to the existing contour group. Instead, use the right-click menu while inside the contour drawing tool, and select Start new contour group. Drawing will then start and you can draw the new contour normally, creating a new contour group for it.

You can also take a contour line from an existing contour group and select "Convert to new contour group" from its right-click context menu (in the Select tool). This will remove the contour from its current contour group and create a new contour group for it.