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Ensure the default values of 'Automatic collapse' and 'automatic tolerance values' are set in the 'Import and Export' branch of preferences window, and import the file named 'level_curves.dxf' using
Files ->Import->DXF-> Import --> DXF...
The result is a model with a collection of straight lines like this:
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To facilitate the work the 'near tangent' lines (with a tolerance) could be joined to reduce the number of curves of the model. To do so, use
Geometry ->Edit->Join->Lines--> Edit --> Join --> Lines,
and select all of them. The result should look like the following figure.
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To create surfaces it is needed to have a set of closed contour lines. It is possible to create extra curves to enclose regions of topologically four curves, to create surfaces defined 'from its boundary'.
Use
Geometry ->Create→Line --> Create --> Line
and pick two existing points, for example create these two new lines:
In some parts, there may be needed some extra point to create the desired line, it is possible to force the division of a curve 'close to a coordinate' using
Geometry ->Edit->Divide->Lines->near --> Edit --> Divide --> Lines --> near point
Select the existing point A, press <ESC> and then the line/s to be divided
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Now we can create a new surface interpolating its boundary curves:
Geometry --> Create ->Create->NURBS > NURBS surface -->By > By contour
And select the boundary curves.
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We are going to smooth a little bit the shape of the courves. Prior curves must be converted to NURBS expression.
Geometry --> Edit ->Edit->Convert to NURBS→Line> Convert to NURBS --> Line
And then modify a little its shape forcing the tangency at joining points.
Geometry --> Edit ->Edit->Lines > Lines operations -->Force > Force to be tangent
And set a very big tolerance angle (between tangents), like 90 degrees
Then lines can be joined using
Geometry ->Edit->Join->Lines--> Edit --> Join --> Lines
At this point we already have the family of 'parallel' smooth curves to be used for the creation of the interpolating surface:
Geometry -->Create->NURBS surface->Parallel > Create --> NURBS surface --> Parallel lines
As can be seen this may be a manual and tedious procedure to re-build a surfaces model depending on the complexity of it, but in some cases this procedure may be very useful to simplify large models.
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An interesting option is to create a single NURBS surface approximating (not interpolating) a cloud of points. It creates a rectangular shape projecting in a direction (in this case, z direction). To do so, use
Geometry --> Create ->Create->NURBS > NURBS surface -->By > By points
and select all the points of the model
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We can create a rectangle
Geometry ->Create->Object->Rectangle--> Create --> Object --> Rectangle
156,1352,0
1178,128,0
Then extrude it to create lateral surface that intersect with the terrain
Utilities -->Copy> Copy... (Lines, Translation, increment z=300, Do extrude: Surfaces)
Now, for intersecting the surfaces use
Geometry ->Edit->Intersection->Surfaces--> Edit --> Intersection --> Surfaces
And select the surfaces
Then you can delete unwanted parts
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A simple way to sample points is creating a mesh, and exporting the coordinates of the nodes as a simple text file. Create a new GiD project using
Files -->New> New
and import another time the DXF 'level_curves.dxf' file.
Generate a mesh (Mesh -->Generate> Generate), and write the coordinates of its nodes using
Files --> Export ->Export->Using > Using template .bas (only mesh) -->XYZ> XYZ
Create again a new model (Files -->New> New) and import the XYZ file as geometric points
Files --> Import ->Import->XYZ > XYZ points...
Ensure the 'Triangulate' extra option is selected in the import options parameters, as shown in the following figure.
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Create again a new model (Files -->New> New) and import the XYZ file but now as mesh nodes, and without connect them with triangles
Files --> Import ->Import->XYZ > XYZ nodes...
We can build a regular square grid using
Geometry ->Create->Geometry -> Create --> Geometry from mesh ->Nodes→grid --> Nodes --> grid surfaces
Enter a grid cell size of 20 units and select all nodes.
A regular grid of surfaces will be created, with z of points approximated from the selected nodes
Using Nodes→grid Nodes --> grid surfaces the z's are approximated with an averaged value based on inverse of distance to a power of close nodes.
Using Triangles→grid Triangles --> grid surfaces (in case the input data are triangles, not just nodes) the z's would interpolated projecting the node over the selected triangles. This option could be more expensive.
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Instead of create surfaces of geometry it is possible to create mesh entities, or export the grid data in a file (ARC/Info grid ASCII format, supported by most 'Geographic Information System' GIS programs). If you export a raster file using
Files ->Export->Nodes→Raster--> Export --> Nodes --> Raster...
then, the raster can be re-imported with
Files --> Import ->Import->Raster > Raster GDAL...
This import option supports several common raster formats like geotiff, ARC/Info ASCII or binary, png, jpg, among others (based on the GDAL library), and allows to create geometry, mesh, write as ARC/Info ASCII, and also sub-sample data for big files.
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GiD 14 incorporates the possibility to obtain a grid from the place of the world we want using:
Files ->Import→Topography-> Import --> Topography...
We must enter the latitude and longitude geographical coordinates of the location we are interested in. In case we do not know its coordinates is possible to try to find them based on the name of the place,
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Note: georeferenced UTM topography usually require too big numbers for the coordinates, especially for the 'y' (e.g. x=427378 y=4579121), this could become a numerical problem for the graphical representation (OpenGL uses float numbers to draw, that mean about 7 significative digits), and for the calibrated tolerances of some algorithms. In case of problems a solution could be use the 'Move' tool to displace the whole model close to the 0,0 origin. It is recommendable to store somewhere (like Ulitities ->Tools->Notes-> Tools --> Notes) the offset used to recover the true coordinates if necessary.