FILTER will remove unwanted data from the triangulation such as long triangles and/or acute triangles. The engine works as an iterative process that starts by removing filtered triangles one-by-one from the edge of the triangulation.
The syntax for using FILTER from the command line is described below.
Use the syntax, filter -h to display this help:
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FILTERING TRIANGULATED SURFACES -ishl file Input shell file with triangulated surface. -oshl file Output shell file with filtered surface. -dir path Define a directory with input files. -angle val Delete triangles that have angle less than 'val'. -area val Delete triangles that have area more than 'val'. -length val Delete triangles that have side longer than 'val'. ______________________________________________ Filter ver 1.65 (MS3D TL) Copyright (C) 2014 Leica Geosystems. |
Use the syntax, filter -v or filter /h to display this usage information:
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Usage: filter [-ishl filename] [-oshl filename] [-angle val] [-area val] [-length val] [-dir dir] Use option -h for more information. |
The FILTER options behave in a similar way as the "Limit.." triangulation options in the MS3D Triangulate by Dialog, as displayed in the image below [also refer to the MS3D documentation, MS3D.chm.]
From MS3D:
Filter Usage Examples
These examples illustrate the use of the 3 main functions; angle, area and length.
This option is used to restrict the creation of a skinny faces (triangles).
The "angle" option only affects skinny triangles on the edge of the surface. Removing such triangles one by one the algorithm goes deeper and deeper into the surface. Triangles inside of the surface are not checked. So acute triangles will not be deleted unless they get exposed at the edge.
Skinny triangles at the edge of the surface is unwanted data. They can be created by triangulation when a surface is large (geometrically) and boundary polygons are not used [Note: use of boundary polygons would prevent the creation of skinny triangles]. This is typically the case when the data comes from aerial surveys or pit scans.
The image below shows the input surface before using Filter.exe, as displayed in MS3D. Notice there are vertical walls around the edges of the surface.
Using the following syntax, those vertical walls with skinny triangles are removed by filter.exe.
filter.exe -ishl Surface.shl -angle 5 -oshl Angle.shl
The following image shows how filter.exe affects triangles located the edge of the surface. If you use a much larger angle, i.e. 50°, many more triangles will be removed from the edge moving inward, as illustrated below.
This option is used to prevent the creation of very large faces. Filter will remove those triangles that have an area greater than the specified value. Like the "angle" option, the deletion is done from the edges of the surface. Therefore, the smaller number used, more of the surface will be deleted.
Starting with this surface, as shown in MS3D with wireframe in gray and faces in cyan color:
Using the following syntax to delete all faces with an area >25,000 sq ft;
filter.exe -ishl Surface.shl -area 25000 -oshl Area.shl
As displayed in MS3D, the resulting surface is shown below in light orange overlain by the input surface in the wireframe. If a smaller value had been specified, even more triangles would have been deleted.
This option is used to restrict the creation of long faces.
filter.exe -ishl Surface.shl -length 1200 -oshl Length.shl
This option removes the faces from the input shell, "Surface.shl" that have a side >1200, and creates the output shell file, "Length.shl" (as shown in MS3D).
Below is the starting, input surface before using Filter.exe, as displayed in MS3D:
Resulting filtered surface created using Filter.exe with the "length" option. Notice the triangles that existed in the input file's "valley" are removed in the output, as well as skinny vertical triangles on the edge of the surface (lower left side in the image below).
