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Using Landscape Thematic Indexes with _EQUATION
Applies to Remsoft Spatial Planning System 2009.9 and higher
Woodstock version 2009.9 includes a complex yield table equation function (_EQUATION) that allows users to develop user defined equations using a variant Dynamic Link Library (DLL) developed by Remsoft and included with the software. The _EQUATION function allows users to bypass the need for programming DLLs to represent more complex yield equations. One elegant feature of _EQUATION is the ability to use landscape thematic indexes (_INDEX) to declare numeric values for basic character based landscape attribute codes.
The purpose of this tech tip is to describe how landscape thematic indexes can be used with _EQUATION to generate yield values.
The Landscape _INDEX keyword is structured as follows:
"*THEME [Description]
BasicCode _INDEX(IndexCode1=Value,IndexCode2=Value,…)
‘BasicCode’ is a user-defined basic attribute code,
‘IndexCode1-2’ are user-defined index codes,
‘Value’ is a real number.
In the example below individual tree weight is estimated using a formula that includes previously declared user defined yield tables quadratic mean diameter (yQMD) and dominant height (yDomHt). However, not all species uses the same constant. 'a' is a thematic index that references a Landscape theme representing tree species.
First the _INDEX values are setup up in the Landscape section:
;Landscape
*THEME species
prad radiata pine _INDEX(a=1.3)
eucs eucalyptus spp. _INDEX(a=1.24)
dfir douglas fir _INDEX(a=1.28)
bare bare ground (area awaiting regeneration) _INDEX(a=0)
Then we can reference the thematic indexes in the equation in the Yields section:
;Yields
*YC ? ? ? ? ? ?
tree_dry_weight _EQUATION (a * yQMD^2 * yDomHt * 10^-4)
Since you cannot reference character strings using _EQUATION, thematic indexes allows the user to associate numeric values to character based landscape attributes.
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