/usr/share/elmerpost/help/dspl.html

<html>
<body>

<img src=figs/elmer.gif><p>

<p>
<h5> Contents: </h5>
<ul>
  <li> <a href=#MeshLines> Mesh Lines </a>
  <li> <a href=#ColorMesh> Color Mesh </a>
  <li> <a href=#ContourLines> Countour Lines </a>
  <li> <a href=#ContourSurfaces> Contour Surfaces and Model Cuts </a>
  <li> <a href=#Vectors> Vector Display </a>
  <li> <a href=#Particles> Particle Dispaly </a>
  <li> <a href=#Spheres> Shepre Display </a>
  <li> <a href=#ColorScale> Color Scale Display </a>
</ul>

<p>
<h4> <a name=MeshLines> Mesh Lines </a> </h4>
<p>
This is currently a on/off switch for displaying mesh lines, for more
versatile version see <a href=#ColorMesh> Color Mesh display.
<p>
<h4> <a name=ColorMesh> Color Mesh Display </a></h4>
<p>
<img src=figs/mesh.gif>
<p>
The Color Mesh display entry lets you define mesh display settings.
You can also select this entry by pressing the button labeled 
'Color Mesh' in the main command window of Elmerpost. Selecting either
the menu entry or pressing the button again will switch the display
of mesh on or off depending on the previous state (the button in the
main window is down if the display mode is on). 
<p>
At the bottom of the display window there is a button labeled: 'Color Variable'.
Pressing this button gives you a list of variables present in Elmerpost which
match current model size. You can select  a variable by double clicking its name
in the. This variable will be used to colorize the element border if the 'Mesh Style'
setting is 'Line' or the surface elements if the 'Mesh Style' is 'Surface'.
The setting 'Surface' doesn't apply to volume elements.
<p>
The 'Edge Style' setting only affects the line display mode. If you select the
value 'Free' for this setting, only the element sides which are connected to
one and only one element are drawn.

<p>
<h4> <a name=ContourLines> Contour Line Display </a></h4>
<p>
<img src=figs/cont.gif>
<p>
Select the field variable for contours by pressing the button labeled 'Color Variable'.
Double click the name to select a variable. The values where the contours are
searched are generated automatically to cover the range of the variable.
The minumum and maximum values of the variable are shown in the 'Min' and 'Max'
entries. You can also set these values yourself. If you also click the keep
button the minumum and maximum values are not changed when selecting a new variable.
<p>
It's also possible to directly change the contour values shown left of the color boxes.
<p>

<h4> <a name=ContourSurfaces> Contour Surfaces and Model Cuts </a> </h4>
<p>
<img src=figs/iso.gif>
<p>
This selection activates the display of isosurfaces or model cuts and gives a panel to edit the
parameters. First the variable from which the isosurfaces are to be extracted must be selected
pressing the button labeled 'Contour Variable'. You can color code the extracted surface by
another variable (which of course might be the same...) by selecting it from the button
'Color Variable'. The threshold values are selected from the top of the window in the
same manner as in the Contour Line Display settings.
<p>
You can select the contour variable to be one of the node coordinate arrays which gives
the capability to have cuts from the model aligned with the model coordinates planes.
Advanced users can also create their own variables, which can be any
functions of the coordinates, using the Math Module of Elmerpost.
<p>
If you want to have lighting effects on the extracted surfaces you must set the
'Surface Normal Variable' to be a normal vector of the 'Contour Variable' at node
points of the element model. Usually this variable can be created by the Math Module
command <em>norm=grad(var)</em>.
<p>
<h4> <a name=Vectors> Vector Display </h4>
<p>
<img src=figs/vector.gif>
<p>
There are three primary variables controlling the display of vector fields.
First is the 'Color Variable' which is used to color code the vectors.
The second variable is the 'Length Variable' which is used to scale the vector
lengths. Both of these are usually set to the length of the vector,
but may be any other variable defined for the element model.
When a vector field variable, say 'Velocity', is read in to Elmerpost there will also
automatically be a scalar variable called 'Velocity_abs' containing the
length of the vector. If you modify a vector field or generate a new
vector inside Elmerpost, you can allways compute the length of the
vector field by the Math Module command
<em> Velocity_abs=sqrt(vdot(Velocity,Velocity))</em>.
The third variable controlling the display of vectors is the 'Arrow Variable' which
is the actual vector field.
<p>
You can also threshold the display of vectors by setting the 'Threshold Variable' to some
field variable and changing the 'Min' and 'Max' values. This way you could display
only vectors that are longer than some threshold value, or display velocity vectors only where
temperature is above some threshold value.
<p>
<h4> <a name=Particles> Particle Display </h4>
<p>
<img src=figs/particle.gif>
<p>
For the particle display mode you need to set the vector field
variable which is used to advect the particles, the 
'Velocity Variable'. Dispite the name of the setting you can
use any vector variable here. Secondly you need a Math Module variable,
say 'part', which contains the following information:
(nop = number of particles)

<ul>
  <li> part(0,0:nop-1) = initial x-coordinate of particles
  <li> part(1,0:nop-1) = initial y-coordinate of particles
  <li> part(2,0:nop-1) = initial z-coordinate of particles
  <li> part(3,0:nop-1) = initial value of the color variable at the place of particles,
initialize to whatever
  <li> part(4,0:nop-1) = element numbers containing the particles, initialize
to your best guess
</ul>
Use this variable for the 'Particle Variable' setting.
<p>
You can select the integration method used to advect the particles to be either 'Euler'
(fast but inaccurate and potentially unstable), 'Runge Kutta' (slower but more accurate). Also you can
set the 'Integration Policy' to either 'Fixed' or 'Adaptive'. With fixed timestep the
'Maximum timestep' setting is used as timestep. With adaptive strategy the timestep is divided
to two halves until the result with previous full step is the same as the
result with two half steps to precision of the 'Absolute error' setting.
<p>
As an example below is a TCL-function 'Integrate', which takes as its argument
the number of particles, the number of timesteps to use in integration
and lastly a 0/1 flag wheter a trace should be leaved when displaying the particles. 
<p>
First in the script a variable 'part' is created which is initialized to contain
requested number of particles randomly placed in the model volume. Secondly the
particles are advected given number of times. A trace of the particle positions
is also  kept in the variable 'ptrace', which may be used later to draw the particle
paths or save the path to a file, etc.
<pre>
proc Integrate { n { nt 1 } { trace 0 } } {

  global NumberOfTimesteps ParticleParticle

  math n=$n
  math {
    part   = 0;
    ptrace = 0;
    t = 0:(n-1);

    xmin=min(min(nodes(0,time(0))));
    xmax=max(max(nodes(0,time(0))));

    ymin=min(min(nodes(1,time(0))));
    ymax=max(max(nodes(1,time(0))));

    zmin=min(min(nodes(2,time(0))));
    zmax=max(max(nodes(2,time(0))));

    part(0,0:(n-1))   = (xmax-xmin)*rand(n) + xmin;
    part(1,0:(n-1))   = (ymax-ymin)*rand(n) + ymin;
    part(2,0:(n-1))   = (zmax-zmin)*rand(n) + zmin;
    part(3:4,0:(n-1)) = 0.0;
    _particle_last = part;
  }

  set ParticleParticle "part"
  UpdateObject;

  display
  if { $trace == 1 } { clear off }
  display

  do i 0 [@ $nt-1] {
    echo "Time: $i"
    if { $i < $NumberOfTimesteps } { timestep $i }
    pintegrate
    math "i=$i; ptrace(0:4,i*n+t)=part"
  } 1

  if { $trace == 1 } { clear on }

  echo "Integration ready"
}
</pre>
<p>
After the particle positions are known the following kind of script may
be used to display the particle trace. The arguments are the same as for
the 'Integrate'-function above.
<pre>
proc Showparticles { n { nt 1 } { trace 0 } } {
  global NumberOfTimesteps

  math n=$n
  math {
     t=0:(n-1);
     part=ptrace(0:4,t);
     _particle_last=ptrace(0:4,t);
  }

  display;
  if { $trace == 1 } { clear off }
  display;

  do i 0 [@ $nt-1] {
    echo "Time: $i"
    math "i=$i; part=ptrace(0:4,i*n+t);"
    display;
    math _particle_last=part
  }

  if { $trace == 1 } { clear on }
}
</pre>

<p>
<h4> <a name=Spheres> Sphere Display </h4>
<p>
<img src=figs/sphere.gif>
<p>
<h4> <a name=ColorScale> Color Scale Display </h4>
<p>
<img src=figs/cols.gif>
<p>
Color scale display uses current colormap to draw a color scale to graphics window.
You can set the lower left corner of the colorscale to a position
by modifying the 'X Position' and 'Y Position' settings. 
The size and shape of the colorscale may be set by modifying the 'Length' and
'Thickness' settings. The numbers shown in the colorscale are taken from
minimum and maximum of the the field variable which can be set by
the 'Color Variable' setting. The number of labels may be set by modifying the
the setting 'Labels'.
<p>

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