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Import points and generate a digital terrain model in a CAD file


Although what interests us at the end of an exercise like this is to generate cross sections along a line axis, calculate cut volumes, embankment, or the profiles themselves, in this section we will see the generation of the digital terrain model from the moment of importing the points, so that it can be replicated by another user. As AutoCAD commands in English are more popular, we will mention them in English.

We will do this exercise using CivilCAD. If you don't have it, at the end we will show you how to download it.

If you want to develop this exercise step by step, you can use the sample file called Sts.txt, Which at the end of the article can indicate how to obtain.

  1. The format of the points

CivilCAD can import coordinates in point format from different nomenclature, in this case we will use data from a survey that has been generated in a txt file, where the points are separated by columns, in the following format: Point number, X coordinate, Y coordinate, Elevation and detail.

  • 1 1718 1655897.899 293.47 XNUMX
  • 2 1458 1655903.146 291.81 XNUMX
  • 3 213 1655908.782 294.19 XNUMX
  • 4 469 1655898.508 295.85 XNUMX FENCE
  • 5 6998 1655900.653 296.2 XNUMX FENCE
  1. Import points

This is done with:  CivilCAD> Points> Terrain> Import

In the panel that is shown, we choose the option NXYZ, Since we are interested in importing the descriptions, we chose the Annotate description option.

Select accept with the button OK  And we choose the file, which in this case is called “Sts.txt“. The process starts importing points and after a few seconds, a message should appear at the bottom indicating how many points have been imported. In this case it should indicate that you imported 778 points.

To be able to see the points, it is necessary to perform an Extent type Zoom. Either with the respective icon or on the keyboard using Z> enter> X> enter.

The size of the points depends on the configuration you have, to change this is done with Format> Point Style, Or by using the command Ddptype.

If you want to see them in the size shown in the image, use the indicated point type and a size of 1.5 absolute units.

As you can see, all the points were imported, and the description was written next to the ones that had it.

Also see that some levels have been created according to the imported data:

  • CVL_PUNTO Contains the points
  • CVL_PUNTO_NUM Contains description
  • CVL_RAD Would contain point data from a radial survey.

The color of the levels can be modified as well as the color of the points by turning them from yellow to ByLayer, so that they acquire the color of the layer and are easier to visualize.

If you have the AutoCAD screen in white, you can change it to black using Tools> Options> Display> Colors… In a dark background color it will be easier to visualize objects in light colors like yellow.

  1. Generate triangulation

Now we need to convert the points we imported into a digital terrain model. For this, we must turn off the layers that we do not need.

This is done using the routine:

CivilCAD> Layers> Leave on.  Then we touch a point and do Enter. With this, only the layer of points should be visible. Also for the next step it is necessary to have all the points visible.

To generate the triangulation we do:

CivilCAD> Altimetry> Triangulation> Terrain.  The lower panel asks us if we want to make them based on existing points or contour lines already drawn on the map. Since what we have are points, we write the letter PThen we do Enter. We select all the objects and at the bottom it should tell us that there are 778 points selected.

We do again Enter, and the system asks us what distance we will use for triangulation at the perimeter points. In this case we will use 20 meters, Considering that the survey was done with a grid of approximately 10 meters.

We wrote 20Then we do Enter.

We indicate as minimum angle 1 Degree we do Enter And this must be the result:

A layer named CVL_TRI has been created that contains the generated 3D faces.

  1. Generate Level Curves

One of the most important aspects of digital model visualization is generating contour lines. This is done with:  CivilCAD> Altimetry> Contour Lines> terrain

Here we indicate that the secondary curves (called in thin CivilCAD) are at each 0.5 meters and the main ones (thick) at each 2.5 meters.

And for the curves to soften at the vertices we will use an 4.4 factor and the result should be the image shown below.


Golgi Alvarez

Writer, researcher, specialist in Land Management Models. He has participated in the conceptualization and implementation of models such as: National Property Administration System SINAP in Honduras, Management Model of Joint Municipalities in Honduras, Integrated Cadastre-Registry Management Model in Nicaragua, Territory Administration System SAT in Colombia . Editor of the Geofumadas knowledge blog since 2007 and creator of the AulaGEO Academy that includes more than 100 courses on GIS - CAD - BIM - Digital Twins topics.

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