Introduction - MDT25

2.1 Introduction

A Digital Terrain Model is made from a job done with 3D and 2D drawing elements having elevation (contour lines, 3D lines, etc.), or alternatively with field data represented by points. These points, conveniently "joined together", make up what is called a scatter plot. The points are represented by their X, Y, Z coordinates and usually by an ordinal number and an associated code. These data organized in lines and columns with defined separators form a point data file. This application also allows one to modify the scatter plot by means of a set of tools that are described in this section.

Estimation of Uncertainties

MDT version 25 enables us to store the uncertainty of the X, Y, Z coordinates of each point. These values can be assigned using the following methods:

• If the points have been surveyed using a GNSS receiver, depending on the format of the files, they may be included in the estimated horizontal and vertical positions. For example, if the data has been taken using the TcpGPS application, the uncertainties will be assigned automatically on importing the points.

• If the points have been surveyed using a Total Station and calculated using the MDT Surveying model, the uncertainties of each point are calculated based on the characteristics of the tool, which should be defined within the properties of the survey.

• Finally, the values of the uncertainties can be assigned by means of a manual entry using the Change Uncertainties command.

It should be considered that the confidence level for the estimation of uncertainties (95% by default) is established in the Surveying settings. See the Customization Manual for more details.

Point Objects

MDT has two ways of representing points: either as blocks having attributes or as special objects (MDT points). The former has the advantage that they can be handled on a computer that does not have MDT installed. Their disadvantage lies in the fact that processing such points is much slower. Independently of the object type, each point stores a name or number, a code and a level, in addition to its coordinates. When the entity is an MDT point, additional attributes can also be included with the observation data for the point (GPS or total stations), hyperlinks, and data defined by the user. To change between one or another representation use the command Tools > Configuration > Points and select at the top the type of representation to be used.

Point coordinates can be modified either with the application's own utilities or directly using the CAD commands, including DELETE, MOVE, ROTATE, UNDO, etc. The difference between both command categories is that the program's commands offer greater possibilities and easier selection possibilities.

Depending on the type of object used to represent points, the attributes appear in separate layers (block type objects) or in the same layer (MDT point objects).

Classification by Levels

The possibility exists of classifying points by levels in accordance with the following initial table:

Level Description Use in Surface

0 Default YES

1 Fillings YES

2 Break lines YES

3 Information NO

4 Stake Out NO

Points belonging to levels 0, 1 and 2 are the only points used to create the digital model with the default configuration. Points belonging to levels 3 and 4, on the contrary, are respectively considered as informative or setting out points.

The configuration can be changed using the Utilities > Configuration > Points > Levels button.

Separation into Groups

Apart from the possible classification by point levels, these can be grouped together in different ways to create point groups with a name. Groups can be created that correspond to different work phases, successive modifications, etc. A point may belong to several groups.