Ground Modelling

Introduction

The triangular ground modelling module works entirely within CAD to calculate a series of triangles to accurately represent the existing ground, design or other surface. This module is designed to be very simple to use and extremely flexible. In addition to mainstream uses for site development and road design it is suitable for a wide range of applications including :-

Landfill

Landform design

Quarries

Earthworks

Sports pitches

Visual Impact analysis

Beach modelling and coastal erosion studies

Hydrographic surveys

Airfield approach studies

KTF's Ground Models are Triangulated Irregular Networks, saved in a separate .kgm file. There are two main ways to create them: Triangulation and Gridding. The Triangulating function builds models typically from 3D entities in the drawing such as Land Survey spot levels and 3D Polylines representing existing linear features (breaklines) or from design 3D Polylines and proposed spot levels. Gridding is usually used with larger models where the level data is read in from DTM files like OS Land-Form PROFILE or LIDAR survey files.

All KTF ground models are stored in ".kgm" files. There is no direct link between the CAD drawing and the ground model file. Every function that uses a ground model reads the model data from the .kgm file i.e. the model is the .kgm file.

With Triangulating there are two main types of source data in the drawing that models are created from :-

1	Points such as spot levels or grid of levels over a site.
2	Joined (or connected) e.g. channels, tops and bottoms of banks represented as 3D Polylines.

Note that the line elements within 3D Polylines will normally be breaklines (or fold lines) that are used to define triangle sides and improve accuracy.

KTF is not able to model vertical surfaces and for example kerbs should be surveyed with around a 20 mm. offset and a 1 metre high retaining wall should "lean" by 40 to 45 mm. To help avoid very narrow triangles channel lines and kerbs etc. should have vertices every 5 to 10 metres – these may be surveyed points or created with menu item Polyline utilities, Additional vertices.

There is no absolute maximum number of points that a model is created from or triangles that are in the model but data should be managed with the same considerations given to large CAD drawings. Models may contain one or over 1 million triangles. Time taken to work on very large survey data drawings will depend, to great extent, on hardware specification.

No limitations exist regarding the number of models (.kgm files) used for a particular project or created from any CAD drawing. Ground models may represent existing or proposed landform and strata etc. and should be given a logical file name. When creating a model there is an option to assign a model type such as a Design model or Strata model in addition to the default general "Ground Model". Models may also be of a nominal or temporary nature and used as part of a design sequence or construction such as representing a horizontal surface for the base of a pond.

In addition to all the menu items in this module that either create a model, produce an output from a model (or models) or provide management and information tools there are some menu items in Design that use a model in 3D road design functions plus the following menu items in the Base module :-

3D utilities, Enquire and define Slope Report gradient between two locations on a model.

3D Polylines, Extend Extend a 3D Polyline to where it "hits" a model.

Annotate and Enhance, Blocks and Text, Random block locating Plant trees in 3D for example.

Remember - the model will only be as good as the data you create it from. Subsequent outputs can only be as good as the model or models being used.

Methodology

It is important when using the KTF ground modelling functions to be aware that :-

1	The model is to be created from suitable 3D drawing entities or DTM file.
2	The model is a series of triangles stored as a .kgm file.

When a model has been created there are a range of outputs including 3D Faces, Contours, Interpolating levels, Sections, Draping (converting 2D entities into 3D), 3D Grid (for viewing in 3D and rendering), Slope arrows (to show downhill slope directions) and Colour mapping (to present cut and fill and ZTV results etc.). When selecting models for outputs use the Preview option to view the triangles to help confirm that you have the correct model in complex projects.