TIN stands for triangulated irregular network. This kind of surface is made up of non-overlapping triangles. Each of the triangles represents a face on the surface.
Triangulated irregular network example (source)
A TIN surface can be created from many different types of elevation data, such as points (e.g. a topographic survey), or contours (e.g. polylines). In general, every point, vertex, or node that represents an elevation will be used to create the TIN surface.
- Efficient storage of data
- Variable level of detail based on surface needs
One of the biggest advantages of TIN surfaces is their efficiency in storing data. In a TIN surface, triangles are only created where elevation points exist. In areas where there is limited data, the TIN surface will also have limited triangles. The same is true in the reverse, where there is lots of elevation information, the surface will reflect that detail accordingly.
Imagine, you are surveying a new project site. You need to collect a lot of detail around the road, bridge, and sidewalk to inform your design. In these areas, you collect 1 point every 1m. You also need to collect some data in the surrounding field to understand drainage patterns, but in these areas, you do not require as much detail. Here you collect 1 point every 10 m.
When you turn your surface data into a TIN surface, the resolution of your surface is directly related to the coverage of your survey points. In the field, your TIN surface will be lower resolution with fewer triangles, while on the roadway your surface will be higher resolution with more triangles.
As you can imagine, this approach means that the data storage size is not directly proportional to the physical size of the site.
- Manual work required to “clean-up” a TIN surface
The main disadvantage of a TIN surface is the level of effort that is required to control the quality of the end product. There is typically a lot of manual work that goes into creating a TIN surface for civil engineering design projects.
Since triangles are generated based on closest elevation nodes only, this can cause problems when the source elevation data includes many different features. For example, if a survey point representing the top of a hydrant is right next to a road point, the TIN surface will connect the two and show a bump in the road.
The job of the civil designer is to ensure that the TIN surface reflects the actual conditions or intended design. This is achieved by creating break lines, adding more points or using other editing techniques. As an example, a break line might be drawn to connect all of the edge of pavement points on a roadway, thus controlling surface behavior, smoothness and continuity.