afe/osse_MkII/README.piv


The frame grabber saves the images to 640x482 pixel jpeg
files with the name ``frame.<timestamp>.<level><a_or_b>.jpg''.

<timestamp> is an integer that inicates the number of milliseconds
since the operation system clock of the PC running the framegrabber,
and is used to mark the time between frames.  

<level> is an integer indicating the vertical level of the tank at 
which the frame was grabbed. 

<a_or_b> marks wether the frame in the file is the first or second
frame of the pair grabbed at a particular level.


OBTAINING VELOCITY VECTOR FIELDS WITH PIV

Once you have a collection of pairs of images, you can extract
velocity fields from them.  The current setup uses MatPIV 1.6.1
(see <http://www.math.uio.no/~jks/matpiv/>.  You should look at the
Online Tutorial, particularly "An example session".  Yes, you have to
do it the not so easy way.  This entails establishing a coordinate
system and masking out regions outside of the fluid flow you are
trying to examine.

In order to use MatPIV, you will need to be able to manually examine
at least one of the images created by the frame grabber.  In their raw
state they may be too dark and have too little contrast to be useful,
so you will have to use The Gimp or Image Magick to add contrast to
one of them.  Save it as the file ``masker.jpg''.

To establish a coordinate system, you will have to use one of the MatPIV
utilities to mark tagged points in the image field.  To create these points,
run the Perl script ``addcross.pl''.  This uses Image Magick to add crosses to
the image in ``masker.jpg'', saves the resulting image as ``worldco1.jpg'', and
displays the same.  You may have to manipulate the first couple of lines of
``addcross.pl'' that determine the horizontal and vertical positioning of the
crosses to get the desired result -- the goal is to have at least four crosses
in the field of the particles you wish to include in the velocity field -- the
parts that you later leave unmasked. 

In Matlab, enter the command definewoco(filename,'+'); , where filename is the
image saved with the crosses, and follow the directions in the MatPIV
documentation.  You should enter the coordinates given in the addcross.pl
script.  The Matlab command mask('masker.jpg','worldco.mat'); will then let you mask out regions where no PIV is to be performed.  These areas should include the outside of the tank, the center of the annulus, and the shadow of the laser.
1	afe	1.1
2			The frame grabber saves the images to 640x482 pixel jpeg
3			files with the name ``frame.<timestamp>.<level><a_or_b>.jpg''.
4
5			<timestamp> is an integer that inicates the number of milliseconds
6			since the operation system clock of the PC running the framegrabber,
7			and is used to mark the time between frames.
8
9			<level> is an integer indicating the vertical level of the tank at
10			which the frame was grabbed.
11
12			<a_or_b> marks wether the frame in the file is the first or second
13			frame of the pair grabbed at a particular level.
14
15
16			OBTAINING VELOCITY VECTOR FIELDS WITH PIV
17
18			Once you have a collection of pairs of images, you can extract
19			velocity fields from them. The current setup uses MatPIV 1.6.1
20			(see <http://www.math.uio.no/~jks/matpiv/>. You should look at the
21			Online Tutorial, particularly "An example session". Yes, you have to
22			do it the not so easy way. This entails establishing a coordinate
23			system and masking out regions outside of the fluid flow you are
24			trying to examine.
25
26			In order to use MatPIV, you will need to be able to manually examine
27			at least one of the images created by the frame grabber. In their raw
28			state they may be too dark and have too little contrast to be useful,
29			so you will have to use The Gimp or Image Magick to add contrast to
30			one of them. Save it as the file ``masker.jpg''.
31
32			To establish a coordinate system, you will have to use one of the MatPIV
33			utilities to mark tagged points in the image field. To create these points,
34			run the Perl script ``addcross.pl''. This uses Image Magick to add crosses to
35			the image in ``masker.jpg'', saves the resulting image as ``worldco1.jpg'', and
36			displays the same. You may have to manipulate the first couple of lines of
37			``addcross.pl'' that determine the horizontal and vertical positioning of the
38			crosses to get the desired result -- the goal is to have at least four crosses
39			in the field of the particles you wish to include in the velocity field -- the
40			parts that you later leave unmasked.
41
42			In Matlab, enter the command definewoco(filename,'+'); , where filename is the
43			image saved with the crosses, and follow the directions in the MatPIV
44			documentation. You should enter the coordinates given in the addcross.pl
45			script. The Matlab command mask('masker.jpg','worldco.mat'); will then let you mask out regions where no PIV is to be performed. These areas should include the outside of the tank, the center of the annulus, and the shadow of the laser.