Data and algorithms

Input Data

TIN Creator requires some combination of polygon, polyline and points ESRI shapefiles as input data. In addition some shapes within the input data can be specified as 'holes'. The triangulation process will then go around these areas leaving them blank. Holes are useful to define areas in a model that you want to keep 'dry' when creating a flood water surface from model results.

Input shapefiles can contain many features, e.g. multiple polygons or polylines (though not combinations of the two). Alternatively multiple shapefiles containing only single features are also compatible with TIN Creator.

After input data are loaded you can select a subset of these data for their TIN generation.

Output Data

TIN (interpolated triangular network) surface produced from an ESRI shapefile containing model node labels. TIN files are given the extension '.htn '. They can be saved to a user selected location or automatically loaded back into Flood Modeller.

Description of Algorithms Used

• Constrained Delauney Triangulation Algorithm (CDT) - Similar to the DT method but doesn't produce intersections with loaded polylines or polygons. Triangulates all areas even inside the polygons.

• Constrained Delauney Triangulation Algorithm With Holes (CDTH ) - Does the same as CDT but excludes any holes specified.

• Confirmed Constrained Delauney Triangulation Algorithm (CCDT ) - Similar to the CDT algorithm but generates TINs of better quality, as it produces less thin triangles. This method adds some pseudo-points on the edge of convex hull, polylines or polygons so we can easily interpolate Z values for any point because any pseudo point will lie between two real points.

• Quality Meshing - This method acts in addition to CDT to ensure triangles which have an angle of less than 20 degrees are not produced. This is achieved by adding pseudo-points where necessary. These are points generated by the triangulation operation rather than points from the source shapefiles .

• Convex Hull - Creates an outline that encompasses all loaded shapefiles , known as a convex hull. With this feature deactivated the triangulation method will only produce separate TINs within each individual polygon. When this feature is activated then a single TIN is created that envelops all loaded shapefiles . If input data consists only of collections of points and polylines then without a convex hull activated no TIN will be produced.