Arch Primitive

Tool Plug-in | Updated: 08-Dec-2012


Create semi-circular (Roman), segmental, equilateral and ogive (lancet) type arches.

This plug-in tool functions in a very similar way to modo's built in primitives and allows you to draw arches aligned to the current view facing, to the workplane, to layers with item transforms and where the item reference (local space) is set. In addition, you can rotate the geometry about it's normal and force it to be centred around the world origin or the workplane centre.

The arch geometry created by this tool has equal length segments that is ideally suited to extrusion and for use with sub-division smoothing and has many uses outside of arch-viz work. For example, the ogive arch shape is used in aerodynamic applications e.g. nose cones, bullets. You can quickly create such geometry by using the Arch Primitive tool to make a polyline ogive arch at the origin, which can then be extruded using modo's Radial Sweep tool.

How to useā€¦

  1. Click on the “Arches” button to activate the tool
  2. Click and drag in the 3D view to create an arch. Drag horizontally to set the width and vertically to set the height.
  3. Change values to interactively adjust the shape, style, size and position of the arch geometry.

Sorry, the video for this tool is being updated. Please, see below for a text description of the features of this tool.

User Interface



Select or switch between the available arch types, including: semi-circular, segmental, equilateral and ogive.
Choose between building a single arch-shaped polygon, its inverted shape, or both, a polygon strip or a polyline arch.
Centre to Origin
Centre the arch geometry around the world origin or the centre of the workplace. This will keep the geometry symmetrical around a central point and rotation will occur around this centre.
Spin CW and Spin CCW
Spin the arch geometry by 90 degrees in a clockwise (CW) or counter-clockwise (CCW) direction. The rotation happens around the arch's move handle or around the mid-point of the arch's span when “Centre to Origin” is set.
Number of segments in the arch; some arch types are limited to even numbers of segments.
Height or depth of the arch. That is to say, the height of the crown of the arch above the spring line.
Intra-Extrados Distance
Sets the distance between the inside and outside of the arch. This value is only used when an arch is created using a polygon strip -- see “Geometry” option, above.