Parent Topic: <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/MODEL|Language">Language</a><hr>
<H4>Variables</H4>
Variables give access to image (layer) pixel values, attribute data
and other values. Variables are identified by a special leading
character (#,%,@,$) followed by 1 to 7 characters.
<P>
<H5>Layer Variables</H5>
Layer variables are identified by the leading character `%'. Layer
variables take on the grey level value of the pixel being processed
for a particular layer (image channel). For example, %3 would take
on the grey level value of the third image channel at the current
pixel position. If a name is used (e.g., %tree), then the
association between the name and an explicit layer is made when the
model is first run using a SET or INPUT statement.
<P>
<PRE>
 Syntax:    %x, %n

 Examples:  %soil,%z,%1,%23
</PRE>
<H5>Attribute Variables</H5>
Attribute variables are identified by the leading character `%' and
a '.'. Attribute variables take on the value of an attribute
associated with the layer through the grey level value. For example,
%2.3 would be evaluated as follows: at the current pixel location,
the grey level value for the second image channel would be used as a
key to a single line of attribute data associated with the layer;
within this line, the list of attributes would be scanned and the
third attribute value extracted; %2.3 would take on this value. Note
that this value could be numeric or character depending on the
actual nature of the attribute.
<P>
<PRE>
 Syntax:    %x.i, %n.i

 Examples:  %slope.2, %5.3
</PRE>
<H5>Subscripts</H5>
It is possible to access the grey level values and attribute data
for adjacent pixels by subscripting layer or attribute variables.
The following diagram shows the subscript syntax and relationship to
the pixel being currently processed (which is [ 0, 0]).
<P>
<PRE>
                [-1,-1]  [ 0,-1]  [ 1,-1]
                [-1, 0]  [ 0, 0]  [ 1, 0]
                [-1, 1]  [ 0, 1]  [ 1, 1]
</PRE>
Examples: %1.2[-1,-1], %1[1,1]<p>
%x is equivalent to %x[0,0]. Subscripted pixels which are outside
the bounds of the image are automatically assigned the value of the
nearest pixel which is inside the image.<p>
Note: it is NOT possible to assign a value to a subscripted pixel.
<P>
<H5>Numeric Variables</H5>
Numeric variables are identified by the leading character `#'.
Numeric variables are used for temporary storage of numeric values.
They have no relation to any layers or attributes and provide a
convenient way of holding results of calculations or user entered
constants.
<P>
<PRE>
 Syntax:    #x

 Examples:  #tree, #t37
</PRE>
<H5>Character Variables</H5>
Character variables are identified by the leading character `$'.
Character variables are used for temporary storage of character
data. They have no relation to any layers or attributes and provide
a convenient way of holding user entered character data.
<P>
<PRE>
 Syntax:    $x

 Examples:  $name,$a
</PRE>
<H5>Numeric Array Variables</H5>
Numeric array variables are identified by the leading character '#'
followed by 1 to 7 characters and an array subscript. Subscripts can
range from 1 to the number of elements in the numeric array.
<P>
<PRE>
 Syntax:  #x[n]

 Examples: #array[7], #colval[127]
</PRE>
Numeric array variables allow access to one dimensional array
information held in PCIDSK array segments [type ARR:181].
<P>
<H5>Special</H5>
Special variables allow access to information about the file and
location information about the pixel being processed. They can be
used within numerical expressions like constants.<p>
Variable Description
<P>
<PRE>
 @x             current x (pixel) processing location
 @y             current y (line ) processing location
 @dbx           size of database in x (pixel) direction
 @dby           size of database in y (line ) direction
 @metrex        size of a pixel in x direction in metres
 @metrey        size of a pixel in y direction in metres
 @geox          x georeferenced centre of current pixel
 @geoy          y georeferenced centre of current pixel
 @sizex         x size of a pixel in georeferenced units
 @sizey         y size of a pixel in georeferenced units
</PRE>
<hr>
Parent Topic: <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/MODEL|Language">Language</a><br>
<a href="http://www.pcigeomatics.com/dev_corner/pcihlp_gateway.html">About PCI Help Gateway</a>