Inputs
Here you can pass the geometry to the Node whose polygons you want to untriangulate.
If you want to limit the function of the Node to one selection, select here the type of the active selection you want to evaluate. You can choose from Points, Edges or Polygons. Requires a polygon selection, which means that other selections will automatically be converted. All points or edges of a polygon must be selected for it to be untriangulated.
Alternatively, an iteration of the point, edge, or polygon indices can be passed to the Node using the Selection input. If there is neither an active selection nor the Selection input is used, all polygons of the geometry will be processed automatically.
If you want to limit the function of the Node to only a part of the geometry, but there is no active selection, you can pass the indices of points, edges or polygons to the Node here. Remember to select the Type that matches the indices.
Here you can, for example, use the name of a selection in quotation marks that you want to read out, e.g., "MySelection". Otherwise, the default entry will use an active selection on the geometry.
You can also use special keywords and logical operations here to create a new selection from scratch or a combination of already saved selections. The following keywords and operations can be used:
- Default: This term causes an active selection currently present on the geometry to be used. If no selection is active, all points will be used.
- odd: This term is used to select all elements that have an odd index number.
- even: This term is used to select all elements that have an even index number.
- all: This selects all elements of the selected type.
- hidden: Selects the hidden elements of the geometry.
- Name of a saved selection: If you enter the name of a saved selection in quotation marks, this selection will be read and used. To use a combination of a saved selection and another keyword or selection, use quotation marks with the selection name.
- Index numbers: You can also use index numbers directly, just as you are used to from the Index Array From String Node.
- Mathematical and logical operations: Mathematical or logical operations can be used to combine selections. Using the string odd – "center" for instance selects all odd elements and then subtracts the selection that has been stored by the name "center". You can use +, -, & (logical and), | (logical or) as well as a comma to combine multiple selections or index sequences.
Enable this option if you want to create a common N-gon from the triangles. The value defined under Angle ("Plane angle") is automatically taken into account here.
With increasing values it can happen that the geometry will change its shape until it collapses completely. In general, you should operate here with low values (e.g., up to 5°) to achieve meaningful results.
Here you can define the maximum permissible Normal angle deviation between adjacent triangles up to which quads or N-gons may be created. Or simply put, if there is a kink between two triangles, you have to define higher values so that they can be converted.
Here you can define how large the interior angle of the resulting quad is allowed to deviate from 90° so that a quad can still be created. The higher the values here, the further the resulting quads are allowed to deviate from a perfectly square shape.
If you imagine the edges of a quad extended as a line beyond the bounding points, angles will form between these lines and the adjacent edges (unless the mesh is planar). The value defined here indicates the maximum permissible angular deviations in the resulting quad. If the deviation were greater, no quad would be created.
The following options can be used to further control the Node function:
Activate this option if the edges of UV Islands and the associated polygon edges should remain unchanged/preserved. Note that unwanted changes might be made to the UV coordinates. However, this should not matter in most cases, since UV coordinates usually become important only after modeling.
Phong edges defined using 
Break Phong Shading will not be affected if this option is activated and will remain unchanged.
Currently, this option applies only to vertex colors. Here, points can store multiple values (here: colors). If the algorithm were to remove associated triangles, the stored values would change. Activate this option to prevent this, and corresponding edges will not be changed or removed.