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<th nowrap width="1%" height="32">P0058</th>
<th nowrap width="98%">Isolabel</th>
<th nowrap width="1%">16th August 1999</th>
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<p><b>Author:</b> John Sheehan, Ian Curington, Andrew Dodd
<b>Version:</b> 1.0
<b>Path:</b> iac_proj/isolabel/</p>
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<h1>Isolabel_core</h1>
<h3>Synopsis</h3>
<p>
A mapper module that adds text labels to isolines. The module processes
the input field data and generates a Point mesh and a list of
text labels. These can be displayed by the text_glyph module.
</p>
<p>
<hr>
<pre>
module Isolabel_core <src_file="isolabel.c"> {
omethod+req update (
.in+read+notify+req,
.in.nnodes+req,
.num_labels+read+notify+req,
.format+read+notify+req,
.out+write,
.string_vals+write
) = "isolabel_update";
Mesh+Node_Data+IPort2 &in;
int+IPort2 num_labels;
string+IPort2 format;
Mesh+OPort2 out {
ncell_sets = 1;
Point cell_set {
ncells => <-.nnodes;
node_connect_list => init_array(ncells, 0, ncells-1);
};
};
string+OPort2 string_vals[];
};
</pre>
<hr>
</p>
<h3>Description</h3>
<p>
The Isolabel_core module generates text annotation labels for isoline
displays. It connects to the field output of the isoline module and generates
a Point mesh and an array of string values. The Point mesh contains the position
of the labels while the string array contains the actual label text at each
point. These outputs can be directly connected to the text_glyph module, which
will then display the labels. The number of labels output and the format of the
label text can both be controlled. The module is designed to work best when
used with an isoline module, however it can be used to generate text labels for
any Mesh with a matching set of scalar Node data.
</p>
<p>
The label placement algorithm is quite simple and works best in a 2D isoline
context. The module subsamples the input node list at even intervals. This
will generate a series of nodes that are regularly spaced throughout the input
data. Provided the input nodes are distributed evenly in space the output
nodes should also be evenly distributed. Although this method works acceptably
in most contexts it should be noted that it is not suitable for animation. Due
to the way the algorithm works the labels move around unpredictably as
parameters are changed. Hence, for example, recording a moving othroslice with
labels would not be possible.
</p>
<h3>Inputs</h3>
<p>
<i><b>&in</b></i>
</p>
<p>
Reference to a set of Field data which should be used by the module to generate
the text labels. The Field should consist of a Mesh and Node Data. Only the
first set of Node data is used and that Node data must be scalar.
</p>
<p>
<i><b>num_labels</b></i>
</p>
<p>
Number of text labels that should be generated. This is an integer parameter.
</p>
<p>
<a name="format">
<i><b>format</b></i>
</a>
</p>
<p>
C style formatting specification string that sets how the Node data values
should be converted into text. By altering this format string the exact format
of the output labels can be controlled. Internally the format string is used
in a call to the sprintf function to perform the necessary conversion. It
should be noted that the User macro <a href="doc_umac.shtml" target="_top">isolabel</a> does
not expose this parameter. Instead it constructs the format string automatically
from a UI control.
</p>
<h3>Outputs</h3>
<p>
<i><b>out</b></i>
</p>
<p>
Point mesh containing the locations of each text label. This output can be
directly input into the text_glyph module to display the generated labels.
If the input mesh contains any transformation data this is copied across to
the output mesh.
</p>
<p>
<i><b>stringvals[]</b></i>
</p>
<p>
String array containing the actual label text that should be displayed. This
output can be directly input into the text_glyph module to display the
generated labels.
</p>
<h3>Utility Macros</h3>
<p>
The low-level Isolabel_core module is used in the Functional Macro Isolabel
and the User Macro isolabel. Additionally, these macros also use the
Isolabel_Params parameter block group, as do the UI macros.
</p>
<h3>Example</h3>
<p>
Two example applications are provided, IsolabelEg1 and IsolabelEg2. These
applications generate text labels for 2D and 3D isoline plots.
</p>
<h3>Files</h3>
<p><i>iac_proj/isolabel/isl_mods.v</i> contains the V definitions of
the Isolabel_Params group and the Isolabel_core module.
</p>
<h3>Other Notes</h3>
<p>
Please refer to AVS documentation for more information on the isoline and
text_glyph modules. This module does not use the AG kit, and should not be
confused with AGContour which also contains isoline labels.
</p>
<p>
The low-level IsolabelMods library containing the module Isolabel_core does not
specify a process. By default the express process will be used.
</p>
<h3>Authors</h3>
<p>
<pre>
John Sheehan, Ian Curington
Advanced Visual Systems, Ltd.
Hanworth Lane, Chertsey, Surrey, UK
KT16 9JX
</pre>
</p>
<p>
<pre>
Andrew Dodd
International AVS Centre
</pre>
</p>
<h3>Contact</h3>
<p>
<pre>
International AVS Centre
Manchester Visualization Centre
Manchester Computing
University of Manchester
Oxford Road
Manchester
United Kingdom
M13 9PL
</pre>
</p>
<h3>See Also</h3>
<p>
Isolabel_Params, Isolabel, IsolabelUI, <a href="doc_umac.shtml" target="_top">isolabel</a>,
IsolabelEg1, IsolabelEg2.
</p>
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