Kursus Matlab di Jakarta Selatan KURSUS MATLAB ONLINE Skripsi, Tesis, DISERTASI 081219449060: KAMI MEMBERIKAN KURSUS MATLAB - KURSUS MATLAB ONLINE Skripsi, Tesis, DISERTASI 081219449060

Synthesizing Geometries for 21st Century Electromagnetics

Interfacing MATLAB with CAD

Lecture 19 1

Lecture Outline

• Text files in MATLAB

• String manipulation in MATLAB

• STL files

• STL files in MATLAB

• Visualizing surface meshes in MATLAB

• Generating faces and vertices using MATLAB

• Converting surfaces meshes from objects on a 3D grid

• Point clouds

• Importing custom polygons into SolidWorks

Lecture 19 Slide 2

Reading and

Writing Text Files

in MATLAB

Opening and Closing Files

A file is opened in MATLAB as read‐only with the following command.

% OPEN ASCII STL FILE

fid = fopen(‘pyramid.STL’,'r'); %’r’ is read-only for safety

if fid==-1

error('Error opening file.');

end

Use ‘w’ to write files.

A file is closed in MATLAB with the following command.

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% CLOSE FILE

fclose(fid);

Open and closing the file is always the first and last thing you do. WARNING! Always close open files!

Lecture 19 4

Reading a Line from the Text File

A line of text is read from the text file using the following command.

% READ A LINE OF TEXT

L = fgetl(fid);

You can read and display an entire text file with the following code.

% READ AND DISPLAY AN ENTIRE TEXT FILE

while feof(fid)==0

% Get Next Line from File

L = fgetl(fid);

% Display the Line of Text

disp(L);

end

Lecture 19 5

Writing a Line to the Text File

A line of text is written to the text file using fprintf().

% WRITE A LINE OF TEXT

fprintf(fid,’solid pyramid\r\n’);

This writes “solid pyramid” to the file followed by carriage line return.

Numbers can also be written to the file.

% Write Facet Normal to File

N = [ 1.234567 68.76543 1.592745 ];

L = ' facet normal %8.6f %8.6f %8.6f\r\n'; fprintf(fid,L,N);

This writes “ facet normal 1.234567e0 6.876543e1 1.592745e0” to the file followed by carriage line return.

Lecture 19 6

ANSI Formatting -- Summary

ESCAPE CHARACTERS

For most cases, \n is sufficient for a single line break. However, if you are creating a file for use with Microsoft Notepad, specify a combination of

\r\n to move to a new line.

CONVERSION CHARACTERS

Lecture 19 7

ANSI Formatting – Conversion Characters

Lecture 19 8

ANSI Formatting – Flags

Action Flag Example

Left‐justify. '–' %-5.2f

Print sign character (+ or –). '+' %+5.2f

Insert a space before the value. ' ' % 5.2f

Pad with zeros. '0' %05.2f

Modify selected numeric conversions:

• For %o, %x, or %X, print 0, 0x, or

0X prefix.

point even when precision is 0.

• For %g or %G, do not remove

trailing zeros or decimal point. '#' %#5.0f

Lecture 19 9

String

Manipulation in

MATLAB

Parsing Strings

A line of text can be parsed into separate words using sscanf().

S = 'Hello Class';

T = sscanf(S,'%s %s');

T =

HelloClass

S = 'Hello Class';

T = sscanf(S,'%*s %s');

T =

Class

skip string

You can also extract numbers from a string using sscanf().

S = 'I am 25 years old and 6 feet tall.'; N =

N = sscanf(S,'%*s %*s %f %*s %*s %*s %f %*s %*s'); 25

Lecture 19 11

Checking for Specific Words in Strings (1 of 3)

You can perform an exact comparison between two strings using strcmp().

s1 = 'cat';

s2 = 'dog'; c =

c = strcmp(s1,s2); 0

s1 = 'cat';

s2 = 'Cat'; c =

c = strcmp(s1,s2); 0

s1 = 'cat';

s2 = 'cat'; c =

c = strcmp(s1,s2); 1

Lecture 19 12

Checking for Specific Words in Strings (2 of 3)

You can do the same camparison, but case insensitive using strcmpi().

s1 = 'cat';

s2 = 'dog'; c =

c = strcmpi(s1,s2); 0

s1 = 'cat';

s2 = 'Cat'; c =

c = strcmpi(s1,s2); 1

s1 = 'cat';

s2 = 'cat'; c =

c = strcmpi(s1,s2); 1

Lecture 19 13

Checking for Specific Words in Strings (3 of 3)

You can find the occurrence of one string inside another using strfind().

s1 = 'University of Texas at El Paso'; s2 = 'Hawaii';

ind = strfind(s1,s2);

ind = []

s1 = 'University of Texas at El Paso'; s2 = 'Texas';

ind = strfind(s1,s2);

ind = 15

Lecture 19 14

Converting Between Strings and Numbers

You can convert a string to a number using str2num().

S = '534';

N = str2num(S);

N = 534

S = '2.74E-10';

N = str2num(S);

N = 2.74E-10

Similarly, you can convert numbers to strings using num2str().

N = 1234;

S = num2str(N);

S = 1234

N = 1.23456789;

S = num2str(N);

S = 1.2346

N = 1.23456789;

S = num2str(N,'%1.6f');

S = 1.234568

Lecture 19 15

STL Files

What is an STL File?

STL – Standard Tessellation Language

This file format is widely used in rapid prototyping. It contains only a triangular mesh of an objects surface. Color, texture, materials, and other attributes are not represented.

They can be text files or binary. Binary is more common because they are more compact. We will look at text files because that is more easily interfaced with MATLAB.

Lecture 19 Slide 17

Surface Mesh

Despite this sphere really being a solid object, it is represented in an STL file by just its surface.

Solid Object

STL Representation

Lecture 19 18

STL File Format

solid name

facet normal nx ny nz

outer loop

vertex vx,1 vy,1 vz,1

vertex vx,2 vy,2 vz,2

This set of text is repeated for every triangle on the surface of the object.



    v1

v2 v1 v3 v1

vertex vx,3 vy,3 vz,3

nˆ 

v

v v v 

endloop

endfacet

endsolid name

   

2 1 3 1



Bold face indicates a keyword; these must appear in lower case. Note that there is a space in “facet normal” and in “outer loop,” while there is no space in any of the keywords beginning with “end.” Indentation must be with spaces; tabs are not allowed. The notation, “{…}+,” means that the contents of the brace brackets can be repeated one or more times. Symbols in italics are variables which are to be replaced with user-specified values. The numerical data in the facet normal and vertex lines are single precision floats, for example, 1.23456E+789. A facet normal coordinate may have a leading minus sign; a vertex coordinate may not.

Lecture 19 19

Example STL File

solid pyramid

facet normal -8.281842e-001 2.923717e-001 -4.781524e-001

outer loop

vertex 4.323172e-018 1.632799e-017 6.495190e-001 vertex 3.750000e-001 7.081604e-001 4.330127e-001 vertex 3.750000e-001 0.000000e+000 0.000000e+000

endloop endfacet

facet normal 0.000000e+000 2.923717e-001 9.563048e-001

outer loop

vertex 7.500000e-001 0.000000e+000 6.495190e-001 vertex 3.750000e-001 7.081604e-001 4.330127e-001 vertex 0.000000e+000 0.000000e+000 6.495190e-001

endloop endfacet

facet normal 8.281842e-001 2.923717e-001 -4.781524e-001

outer loop

vertex 3.750000e-001 -1.632799e-017 0.000000e+000 vertex 3.750000e-001 7.081604e-001 4.330127e-001 vertex 7.500000e-001 0.000000e+000 6.495190e-001

endloop endfacet

facet normal 0.000000e+000 -1.000000e+000 0.000000e+000

outer loop

vertex 3.750000e-001 0.000000e+000 0.000000e+000 vertex 7.500000e-001 0.000000e+000 6.495190e-001 vertex 0.000000e+000 0.000000e+000 6.495190e-001

endloop endfacet

endsolid pyramid

An STL file is essentially just a list of all the triangles on the surface of an object.

Each triangle is defined with a surface normal and the position of the three vertices.

Lecture 19 Slide 20

A Single Triangle

facet normal -8.281842e-001 2.923717e-001 -4.781524e-001

outer loop

vertex 4.323172e-018 1.632799e-017 6.495190e-001 vertex 3.750000e-001 7.081604e-001 4.330127e-001 vertex 3.750000e-001 0.000000e+000 0.000000e+000

endloop endfacet

Vertex 3

1. Facet normal must follow right‐hand rule and point outward from object.

b) Don’t depend on it!

2. Adjacent triangles must have two

common vertices.

3. STL files appear to be setup to handle

arbitrary polygons. Don’t do this.

Facet Normal

Vertex 1

Vertex 2

Lecture 19 Slide 21

Warnings About Facet Normals

• Since the facet normal can be calculated from the vertices using the right-hand rule, sometimes the facet normal in the STL file contains other information like shading, color, etc.

• Don’t depend on the right-hand rule being followed.

• Basically, don’t depend on anything!

Lecture 19 22

Reading/Writing

STL Files in

MATLAB

How to Store the Data

We have N facets and ≤ 3N vertices to store in arrays.

F(N,3) Array of triangle facets

V(?,3) Array of triangle vertices

Many times, the number of vertices is 3N. Observing that many of the triangle facets share vertices, there will be redundant vertices

Lecture 19 24

Lazy Array of Vertices (1 of 2)

vx,1

vy ,1

vz,1 

 

V vx,2



vy ,2



vz,2  8



 

vx,M

V is an array

vy ,M

vz,M 

containing the 6

position of all the

vertices in Cartesian 9

coordinates.

M is the total number of

vertices. 1

Lecture 19

3 11

10 25

Lazy Array of Vertices (2 of 2)

There is redundancy here. Twelve vertices are stored, but the device is really only composed of four.

While an inefficient representation,

this is probably not worth your time fixing.

SolidWorks exports a lazy array of vertices.

Kursus Matlab di Jakarta Selatan KURSUS MATLAB ONLINE Skripsi, Tesis, DISERTASI 081219449060

Selasa, 13 Januari 2015

KAMI MEMBERIKAN KURSUS MATLAB - KURSUS MATLAB ONLINE Skripsi, Tesis, DISERTASI 081219449060

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