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READ_stl.m
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function [coordVERTICES,varargout] = READ_stl(stlFILENAME,varargin)
% READ_stlascii Read mesh data in the form of an <*.stl> file
%==========================================================================
% FILENAME: READ_stl.m
% AUTHOR: Adam H. Aitkenhead
% INSTITUTION: The Christie NHS Foundation Trust
% CONTACT: [email protected]
% DATE: 29th March 2010
% PURPOSE: Read mesh data in the form of an <*.stl> file.
%
% USAGE:
%
% [coordVERTICES,coordNORMALS,stlNAME] = READ_stl(stlFILENAME,stlFORMAT)
%
% INPUT PARAMETERS:
%
% stlFILENAME - String - Mandatory - The filename of the STL file.
%
% stlFORMAT - String - Optional - The format of the STL file:
% 'ascii' or 'binary'
%
% OUTPUT PARAMETERS:
%
% coordVERTICES - Nx3x3 array - Mandatory
% - An array defining the vertex positions
% for each of the N facets, with:
% 1 row for each facet
% 3 cols for the x,y,z coordinates
% 3 pages for the three vertices
%
% coordNORMALS - Nx3 array - Optional
% - An array defining the normal vector for
% each of the N facets, with:
% 1 row for each facet
% 3 cols for the x,y,z components of the vector
%
% stlNAME - String - Optional - The name of the STL object.
%
%==========================================================================
%==========================================================================
% VERSION USER CHANGES
% ------- ---- -------
% 100329 AHA Original version
% 100513 AHA Totally reworked the code. Now use textscan to read the
% file all at once, rather than one line at a time with
% fgetl. Major speed improvment.
% 100623 AHA Combined code which reads ascii STLS and code which reads
% binary STLs into a single function.
% 101126 AHA Small change to binary read code: Now use fread instead
% of fseek. Gives large speed increase.
%==========================================================================
%==========================================================================
% STL ascii file format
%======================
% ASCII STL files have the following structure. Technically each facet
% could be any 2D shape, but in practice only triangular facets tend to be
% used. The present code ONLY works for meshes composed of triangular
% facets.
%
% solid object_name
% facet normal x y z
% outer loop
% vertex x y z
% vertex x y z
% vertex x y z
% endloop
% endfacet
%
% <Repeat for all facets...>
%
% endsolid object_name
%==========================================================================
%==========================================================================
% STL binary file format
%=======================
% Binary STL files have an 84 byte header followed by 50-byte records, each
% describing a single facet of the mesh. Technically each facet could be
% any 2D shape, but that would screw up the 50-byte-per-facet structure, so
% in practice only triangular facets are used. The present code ONLY works
% for meshes composed of triangular facets.
%
% HEADER:
% 80 bytes: Header text
% 4 bytes: (int) The number of facets in the STL mesh
%
% DATA:
% 4 bytes: (float) normal x
% 4 bytes: (float) normal y
% 4 bytes: (float) normal z
% 4 bytes: (float) vertex1 x
% 4 bytes: (float) vertex1 y
% 4 bytes: (float) vertex1 z
% 4 bytes: (float) vertex2 x
% 4 bytes: (float) vertex2 y
% 4 bytes: (float) vertex2 z
% 4 bytes: (float) vertex3 x
% 4 bytes: (float) vertex3 y
% 4 bytes: (float) vertex3 z
% 2 bytes: Padding to make the data for each facet 50-bytes in length
% ...and repeat for next facet...
%==========================================================================
if nargin==2
stlFORMAT = lower(varargin{1});
else
stlFORMAT = 'auto';
end
%If necessary, identify whether the STL is ascii or binary:
if strcmp(stlFORMAT,'ascii')==0 && strcmp(stlFORMAT,'binary')==0
stlFORMAT = IDENTIFY_stl_format(stlFILENAME);
end
%Load the STL file:
if strcmp(stlFORMAT,'ascii')
[coordVERTICES,coordNORMALS,stlNAME] = READ_stlascii(stlFILENAME);
elseif strcmp(stlFORMAT,'binary')
[coordVERTICES,coordNORMALS] = READ_stlbinary(stlFILENAME);
stlNAME = 'unnamed_object';
end %if
%Prepare the output arguments
if nargout == 2
varargout(1) = {coordNORMALS};
elseif nargout == 3
varargout(1) = {coordNORMALS};
varargout(2) = {stlNAME};
end
end %function
%==========================================================================
function [stlFORMAT] = IDENTIFY_stl_format(stlFILENAME)
% IDENTIFY_stl_format Test whether an stl file is ascii or binary
% Open the file:
fidIN = fopen(stlFILENAME);
% Check the file size first, since binary files MUST have a size of 84+(50*n)
fseek(fidIN,0,1); % Go to the end of the file
fidSIZE = ftell(fidIN); % Check the size of the file
if rem(fidSIZE-84,50) > 0
stlFORMAT = 'ascii';
else
% Files with a size of 84+(50*n), might be either ascii or binary...
% Read first 80 characters of the file.
% For an ASCII file, the data should begin immediately (give or take a few
% blank lines or spaces) and the first word must be 'solid'.
% For a binary file, the first 80 characters contains the header.
% It is bad practice to begin the header of a binary file with the word
% 'solid', so it can be used to identify whether the file is ASCII or
% binary.
fseek(fidIN,0,-1); % Go to the start of the file
firsteighty = char(fread(fidIN,80,'uchar')');
% Trim leading and trailing spaces:
firsteighty = strtrim(firsteighty);
% Take the first five remaining characters, and check if these are 'solid':
firstfive = firsteighty(1:min(5,length(firsteighty)));
% Double check by reading the last 80 characters of the file.
% For an ASCII file, the data should end (give or take a few
% blank lines or spaces) with 'endsolid <object_name>'.
% If the last 80 characters contains the word 'endsolid' then this
% confirms that the file is indeed ASCII.
if strcmp(firstfive,'solid')
fseek(fidIN,-80,1); % Go to the end of the file minus 80 characters
lasteighty = char(fread(fidIN,80,'uchar')');
if findstr(lasteighty,'endsolid')
stlFORMAT = 'ascii';
else
stlFORMAT = 'binary';
end
else
stlFORMAT = 'binary';
end
end
% Close the file
fclose(fidIN);
end %function
%==========================================================================
%==========================================================================
function [coordVERTICES,coordNORMALS,stlNAME] = READ_stlascii(stlFILENAME)
% READ_stlascii Read mesh data in the form of an ascii <*.stl> file
% Read the ascii STL file
fidIN = fopen(stlFILENAME);
fidCONTENTcell = textscan(fidIN,'%s','delimiter','\n'); %Read all the file
fidCONTENT = fidCONTENTcell{:}(logical(~strcmp(fidCONTENTcell{:},''))); %Remove all blank lines
fclose(fidIN);
% Read the STL name
if nargout == 3
line1 = char(fidCONTENT(1));
if (size(line1,2) >= 7)
stlNAME = line1(7:end);
else
stlNAME = 'unnamed_object';
end
end
% Read the vector normals
if nargout >= 2
stringNORMALS = char(fidCONTENT(logical(strncmp(fidCONTENT,'facet normal',12))));
coordNORMALS = str2num(stringNORMALS(:,13:end));
end
% Read the vertex coordinates
facetTOTAL = sum(strcmp(fidCONTENT,'endfacet'));
stringVERTICES = char(fidCONTENT(logical(strncmp(fidCONTENT,'vertex',6))));
coordVERTICESall = str2num(stringVERTICES(:,7:end));
cotemp = zeros(3,facetTOTAL,3);
cotemp(:) = coordVERTICESall;
coordVERTICES = shiftdim(cotemp,1);
end %function
%==========================================================================
%==========================================================================
function [coordVERTICES,coordNORMALS] = READ_stlbinary(stlFILENAME)
% READ_stlbinary Read mesh data in the form of an binary <*.stl> file
% Open the binary STL file
fidIN = fopen(stlFILENAME);
% Read the header
fseek(fidIN,80,-1); % Move to the last 4 bytes of the header
facetcount = fread(fidIN,1,'int32'); % Read the number of facets in the stl file
% Initialise arrays into which the STL data will be loaded:
coordNORMALS = zeros(facetcount,3);
coordVERTICES = zeros(facetcount,3,3);
% Read the data for each facet:
for loopF = 1:facetcount
tempIN = fread(fidIN,3*4,'float');
coordNORMALS(loopF,1:3) = tempIN(1:3); % x,y,z components of the facet's normal vector
coordVERTICES(loopF,1:3,1) = tempIN(4:6); % x,y,z coordinates of vertex 1
coordVERTICES(loopF,1:3,2) = tempIN(7:9); % x,y,z coordinates of vertex 2
coordVERTICES(loopF,1:3,3) = tempIN(10:12); % x,y,z coordinates of vertex 3
fread(fidIN,1,'int16'); % Move to the start of the next facet. Using fread is much quicker than using fseek(fidIN,2,0);
end %for
% Close the binary STL file
fclose(fidIN);
end %function
%==========================================================================