This option is used to Null (remove) Triangles by Angle and Length.
Continue down the page to see the Null Triangles by Angle and Length option.
To Null Triangles by Angle and Length, Use: Tins => Null => by Angle/Length
Firstly select the Tin to null the triangles from the drop down list, in this example we have selected ‘survey’.
Type in the Angle and Length values and also the Combined Angle and Length values required. The values shown in the panel below are standard default values that will work most of the time.
Hit the <Null> Button to null the triangles.
Note: The Null by Angle and Length option nulls triangles from the outermost triangles working inwards. As the triangles are nulled, the next triangles are tested and nulled until the process is stopped by breaklines or that there are no triangles that match the values.
The Angle option tests a triangle to see if it has an external side, that is not a breakline with an angle in it less than the specified angle, and if the angle is less, then the triangle is nulled.
The Length option tests a triangle to see if it has an external side, that is not a breakline greater than the specified length, and if the length is larger, then the triangle is nulled.
For the combined case, a triangle is nulled if it has an external side that is not a breakline, and the sum of the 2 angles on it is less than the combined angle and also has a length that is greater than the specified combined length.
The triangles have been nulled to the values from the panel.
The Length value has been lowered to 30m and the <Null> button hit again, the triangles have been nulled – but there are now gaps appearing in the triangulation.
The Length value has been adjusted to 50m and the <Null> button reapplied.
Important Note: The setting values for this option are stored by the triangulation and the option values are automatically re-run when the triangulation. To turn the test off, just set the panel fields to blank (delete).