Starting data

The starting data is the file topo_nlc.dat, that is a text file with xyz of a grid (5800 points)

-9400 -2884100 1557.5228971414
-9201.7543859649 -2884100 1558.9433292625
...
1900 -2864400 1564.971922013

Files->Import->XZY points...

It is a flat topography, for tutorial purposes will scale z by 50 with Utilities->Move... tool

Note: the move tool could be used also to scale a model if it is represented in unwanted units (e.g. from inches to meters), and to translate the model near the (0,0,0) coordinates origin. 

A common graphical problems is that topographic models are mapped from the curved earth to a planar representation with UTM projection and this could become in too big x,y 2D coordinates (model box far from the origin). This is a graphic problem drawing with OpenGL that uses float real numbers for coordinates (about 7-8 significant digits). Staircase graphical artifacts, and the selection in screen could become a little displaced of the entity drawn. An easy solution is to translate the model in XY near the origin.

How to create a surface model?

The model has only points, not surfaces. There are different ways to create surfaces

• Connect with '2D Delaunay triangulation'

It could be done selecting a checkbox when importing or after with process commands (Mescape Meshing ConnectPoints CreateSurfaces)

Delaunay triangulated surfaces

• Create a single smooth NURBS surface approximating the cloud of points

Geometry->Create->NURBS surface->By points

Single NURBS surface approximated

• Re-construct surfaces from triangle mesh

First Import xyz as nodes (not points!), connecting with triangles

Files->Import->XZY nodes...

and then 

Geometry->Create->Geometry from mesh->NURBS patches

This tool is not recommended in general, because it is not robust enough. It try to create smooth curves joining sharp edges, find closed regions and create smooth NURBS surfaces bounded by the curves and approximating the inner shape based on the shape of the mesh.

Reconstructed NURBS surfaces

• Reconstruct surf-meshes from mesh

Geometry->Create->Surface mesh

The 'surface-mesh' is a kind of GiD's pseudo-surface, that standard curves as boundary, but its inner shape is defined by a triangulation.

The next image show several surface-mesh entities, one of them is showing the inner edges of its underlying mesh.

Reconstructed surface-mesh

This entity is not a CAD standard surface, and can't be exported in exchange formats. Also most geometrical edit GiD tools can not be used with this kind of entity, for example intersection surface-surface, surface-curve, split, etc. are not available. Basically the only available tool is that can be re-meshed.