Scripting Export Mesh - Revision history

WikiSysop: /* Getting started */

2008-05-14T11:36:23Z

Getting started

WikiSysop: /* Getting started */

2008-05-14T11:26:14Z

Getting started

WikiSysop: /* Export a mesh */

2008-04-15T11:35:16Z

Export a mesh

WikiSysop: /* Verification */

2008-04-15T11:28:34Z

Verification

WikiSysop at 11:25, 15 April 2008

2008-04-15T11:25:20Z

WikiSysop at 11:14, 15 April 2008

2008-04-15T11:14:58Z

WikiSysop: /* Writing the data to file */

2008-04-15T11:13:20Z

Writing the data to file

WikiSysop: /* Standalone scripts */

2008-04-15T11:09:12Z

Standalone scripts

WikiSysop: /* Writing the data to file */

2008-04-15T11:07:23Z

Writing the data to file

WikiSysop: /* Writing the data to file */

2008-04-15T11:05:46Z

Writing the data to file

@@ Line 44: / Line 44: @@
 </pre>
-This was a bit of a divergence from the tutorial, don't put this in your script unless you specifically wanted a mesh of the matrix as well. Please be aware that if you use this code, it will generate a tetrahedral mesh and so the code below will need to be extended to accommodate that.
+This was a bit of a divergence from the tutorial, don't put this in your script unless you specifically wanted a mesh of the matrix as well. If you do use this, please be aware that it will generate a tetrahedral mesh and the code below will need to be extended to accommodate these elements.
 The problem we are now faced with is how do we transfer this mesh from memory to the hard disk in the file format that we want so that it can be understood by our software of choice? Read on to find out.

@@ Line 33: / Line 33: @@
 </pre>
-We declare <code>mesh</code> to be an instance of [http://texgen.sourceforge.net/api/class_tex_gen_1_1_c_mesh.html CMesh] and then use it to store a volume mesh of the textile. So with just a few lines of code we now have a volume mesh of the textile stored in memory. The problem we are now faced with is how do we transfer this mesh from memory to the hard disk in the file format that we want so that it can be understood by our software of choice? Read on to find out.
+We declare <code>mesh</code> to be an instance of [http://texgen.sourceforge.net/api/class_tex_gen_1_1_c_mesh.html CMesh] and then use it to store a volume mesh of the textile. So with just a few lines of code we now have a volume mesh of the textile stored in memory. Note that this is just a mesh of the yarns, the volume between the yarns (i.e. the matrix volume) is not meshed. If you wanted to get a mesh of the yarns and matrix together you need to use the <code>CMesher</code> class instead, like this:
 ==Defining the file format==

@@ Line 1: / Line 1: @@
 ==Export a mesh==
-In the [[Scripting Guide]] section you learnt how to create TexGen models from Python scripts. In this tutorial I will explain how to get a volume mesh of the textile and save it to an arbitrary file format. This is a fairly common task but unfortunately one that must often be repeated due to the fact that there is very little standardisation on the file format for meshes. Each software package uses its own mesh file format and so we must learn to read and write to these different formats. Fortunately the Python language is ideal for performing these tasks with relative ease.
+In the [[Scripting Create Models]] section you learnt how to create TexGen models from Python scripts. In this tutorial I will explain how to get a volume mesh of the textile and save it to an arbitrary file format. This is a fairly common task but unfortunately one that must often be repeated due to the fact that there is very little standardisation on the file format for meshes. Each software package uses its own mesh file format and so we must learn to read and write to these different formats. Fortunately the Python language is ideal for performing these tasks with relative ease.
 ==Standalone scripts==

@@ Line 146: / Line 146: @@
   python myscript.py
-replacing <code>myscript.py</code> with the name of the script your created and ensuring you have a textile model named <code>textile.tg3</code> in the some folder as the script. If it ran successfully you should see a file named <code>mesh.vtk</code> being created. Load this up into [http://www.paraview.org/ ParaView] and you should a mesh of your textile.
+replacing <code>myscript.py</code> with the name of the script your created and ensuring you have a textile model named <code>textile.tg3</code> in the some folder as the script. If it ran successfully you should see a file named <code>mesh.vtk</code> being created. Load this up into [http://www.paraview.org/ ParaView] and you should see a mesh of your textile.
-When writing your own scripts it is likely that it will not work straight away, so it is a good idea to check the output of your script at each step with a text editor to ensure that it is writing exactly what you want. This will enable you to isolate bugs early on and one at a time rather than having to fix a long script contain numerous bugs. The [http://docs.python.org/tut/node5.html#SECTION005200000000000000000 print statement] is your friend when it comes to debugging, it can be used to print out values and verify that they are what you expect.
+When writing your own scripts it is unlikely that they will work straight away (even for professional programmers), so it is a good idea to check the output of your script at each step with a text editor to ensure that it is writing exactly what you want. This will enable you to isolate bugs early on and one at a time rather than having to fix a long script containing numerous bugs. The [http://docs.python.org/tut/node5.html#SECTION005200000000000000000 print statement] is your friend when it comes to debugging, it can be used to print out values and verify that they are what you expect.

← Older revision		Revision as of 11:25, 15 April 2008
Line 139:		Line 139:
	file.write("12\n")		file.write("12\n")
	</pre>		</pre>
		+
		+	==Verification==
		+
		+	The first thing to do now is to run the script from the command line like so:
		+
		+	python myscript.py
		+
		+	replacing <code>myscript.py</code> with the name of the script your created and ensuring you have a textile model named <code>textile.tg3</code> in the some folder as the script. If it ran successfully you should see a file named <code>mesh.vtk</code> being created. Load this up into [http://www.paraview.org/ ParaView] and you should a mesh of your textile.
		+
		+	When writing your own scripts it is likely that it will not work straight away, so it is a good idea to check the output of your script at each step with a text editor to ensure that it is writing exactly what you want. This will enable you to isolate bugs early on and one at a time rather than having to fix a long script contain numerous bugs. The [http://docs.python.org/tut/node5.html#SECTION005200000000000000000 print statement] is your friend when it comes to debugging, it can be used to print out values and verify that they are what you expect.

← Older revision		Revision as of 11:14, 15 April 2008
Line 91:		Line 91:
	The VTK file format defines wedges to be of element type 13 and hexes to be of element type 12.		The VTK file format defines wedges to be of element type 13 and hexes to be of element type 12.

−	That's it, you should now have a script which reads a TexGen tg3 file, extracts a mesh from it and writes the contents to a file in the VTK legacy file format.	+	That's it, you should now have a script which reads a TexGen tg3 file, extracts a mesh from it and writes the contents to a file in the VTK legacy file format. Your Python script should look like this:
		+
		+	<pre>
		+	from TexGen.Core import *
		+
		+	# Read in the textile
		+	ReadFromXML('textile.tg3')
		+
		+	# Get a hold of the textile we just loaded in
		+	textile = GetTextile()
		+
		+	# Create a mesh instance
		+	mesh = CMesh()
		+	# Add the volume of the textile to the mesh
		+	textile.AddVolumeToMesh(mesh, True)
		+
		+	file = open("mesh.vtk", "w")
		+
		+	# Write the header
		+	file.write("# vtk DataFile Version 2.0\n")
		+	file.write("Textile mesh data\n")
		+	file.write("ASCII\n")
		+	file.write("DATASET UNSTRUCTURED_GRID\n")
		+
		+	# Write the points
		+	file.write("POINTS %d float\n" % mesh.GetNumNodes())
		+	for node in mesh.GetNodes():
		+	file.write("%g %g %g\n" % (node.x, node.y, node.z))
		+
		+	# Get element information from the mesh
		+	wedgeIndices = list(mesh.GetIndices(CMesh.WEDGE))
		+	hexIndices = list(mesh.GetIndices(CMesh.HEX))
		+	numWedges = len(wedgeIndices)/6
		+	numHexes = len(hexIndices)/8
		+
		+	# Write the element information
		+	file.write("CELLS %d %d\n" % (numWedges+numHexes, numWedges7+numHexes9))
		+	for i in range(numWedges):
		+	file.write("6 %d %d %d %d %d %d\n" % tuple(wedgeIndices[i6:(i+1)6]))
		+	for i in range(numHexes):
		+	file.write("8 %d %d %d %d %d %d %d %d\n" % tuple(hexIndices[i8:(i+1)8]))
		+
		+	file.write("CELL_TYPES %d\n" % (numWedges+numHexes))
		+	for i in range(numWedges):
		+	file.write("13\n")
		+	for i in range(numHexes):
		+	file.write("12\n")
		+	</pre>

@@ Line 43: / Line 43: @@
 ==Writing the data to file==
-Now that we have decide what format the data will be written in, let's get down to actually writing it. First we will open a file for writing:
+Now that we have decided what format the data will be written in, let's get down to actually writing it. First we will open a file for writing:
   file = open("mesh.vtk", "w")
 See the [http://docs.python.org/tut/node9.html#SECTION009200000000000000000 Python tutorial section 7.2] for more details on writing to files in Python. Next we need to write the header:
@@ Line 62: / Line 62: @@
 The % operator is known as the string formatting or interpolation operator. It is important to understand how this works when writing data to files in ASCII format. Read the [http://docs.python.org/tut/node9.html#SECTION009100000000000000000 Python tutorial section 7.1] and [http://docs.python.org/lib/typesseq-strings.html Python library reference 3.6.2] for more information on this.
-It this point, if you run the script it should create a valid VTK file that you can load into the free [http://www.paraview.org/ ParaView] visualisation software. You may want to try this now to check that what you have done so far works correctly. Initially you will not see anything when loaded into ParaView because we have just defined points and nothing else. In order to visualise these points you must apply the Glyph filter. Assuming this works, let's continue and write the elements.
+At this point, if you run the script it should create a valid VTK file that you can load into the free [http://www.paraview.org/ ParaView] visualisation software. You may want to try this now to check that what you have done so far works correctly. Initially you will not see anything when loaded into ParaView because we have just defined points and nothing else. In order to visualise these points you must apply the Glyph filter. Assuming this works, let's continue and write the elements.
 Defining the elements is a little more tricky because there are different types of elements. When meshing the yarns TexGen will use a mix of wedge and hexahedral elements, so we only need to deal with these element types. The [http://texgen.sourceforge.net/api/class_tex_gen_1_1_c_mesh.html CMesh] class stores a long list of indices for each element type. For example, a mesh containing 2 wedge elements and 3 hex elements would contain a list of 12 indices for the wedges and a list of 24 for the hex elements. The first thing to do is to define some variables to contain this data:
@@ Line 71: / Line 71: @@
 numHexes = len(hexIndices)/8
 </pre>
-Next we actually write the data to the file similarly to the way the points where written:
+Next we actually write the data to the file similarly to the way the points were written:
 <pre>
 file.write("CELLS %d %d\n" % (numWedges+numHexes, numWedges*7+numHexes*9))
@@ Line 90: / Line 90: @@
 </pre>
 The VTK file format defines wedges to be of element type 13 and hexes to be of element type 12.

@@ Line 11: / Line 11: @@
   from TexGen.Core import *
-You don't need to do this if you go through the GUI because this step is done automatically for you. Note that by adding this line does not prevent you from running your scripts through the GUI.
+Note that by adding this line does not prevent you from running your scripts through the GUI as well.
 ==Getting started==

@@ Line 45: / Line 45: @@
 Now that we have decide what format the data will be written in, let's get down to actually writing it. First we will open a file for writing:
   file = open("mesh.vtk", "w")
-See the [http://docs.python.org/tut/node9.html#SECTION009200000000000000000 Python tutorial] for more details on writing to files in Python. Next we need to write the header:
+See the [http://docs.python.org/tut/node9.html#SECTION009200000000000000000 Python tutorial section 7.2] for more details on writing to files in Python. Next we need to write the header:
 <pre>
 # Write the header
@@ Line 60: / Line 60: @@
 	file.write("%g %g %g\n" % (node.x, node.y, node.z))
 </pre>
-The % operator is known as the string formatting or interpolation operator. It is important to understand how this works when writing data to files in ASCII format. Read the [http://docs.python.org/tut/node9.html#SECTION009100000000000000000 Python tutorial] and [http://docs.python.org/lib/typesseq-strings.html Python library reference] for more information on this.
+The % operator is known as the string formatting or interpolation operator. It is important to understand how this works when writing data to files in ASCII format. Read the [http://docs.python.org/tut/node9.html#SECTION009100000000000000000 Python tutorial section 7.1] and [http://docs.python.org/lib/typesseq-strings.html Python library reference 3.6.2] for more information on this.
 It this point, if you run the script it should create a valid VTK file that you can load into the free [http://www.paraview.org/ ParaView] visualisation software. You may want to try this now to check that what you have done so far works correctly. Initially you will not see anything when loaded into ParaView because we have just defined points and nothing else. In order to visualise these points you must apply the Glyph filter. Assuming this works, let's continue and write the elements.

← Older revision		Revision as of 11:05, 15 April 2008
Line 79:		Line 79:
	file.write("8 %d %d %d %d %d %d %d %d\n" % tuple(hexIndices[i8:(i+1)8]))		file.write("8 %d %d %d %d %d %d %d %d\n" % tuple(hexIndices[i8:(i+1)8]))
	</pre>		</pre>
		+	Here I have made use of slicing (wedgeIndices'''['''i6''':'''(i+1)6''']''') to reduce the amount of code necessary to output the data. See the [http://docs.python.org/tut/node5.html#SECTION005140000000000000000 Python tutorial section 3.1.4] for information about how slicing works.
		+
		+	And finally we need to output the type of each of these elements:
		+	<pre>
		+	file.write("CELL_TYPES %d\n" % (numWedges+numHexes))
		+	for i in range(numWedges):
		+	file.write("13\n")
		+	for i in range(numHexes):
		+	file.write("12\n")
		+	</pre>
		+	The VTK file format defines wedges to be of element type 13 and hexes to be of element type 12.