6.5 Show diameter distribution

Show diameter distribution

Distribution charts are often useful in data analysis. Field-Map provides with the functionality for such purpose:

procedure ShowDistributionChart( TableOrLayer :TObjectWrapper; 
                                 const AttributeName_ :string; 
                                 const NullAsZero_ :Boolean;
                                 const ClassDef_ :variant; 
                                 const Xlabel_,ChartLabel_,Options_ :string);

Data come from project layer or table (e.g. query result).

NullAsZero parameter specifies whether missing values are assumed to be zero or skipped from the calculations.

ClassDef parameter specifies classes of a distribution. It can be represented by a single value which represents width of the class. In this case all classes are of the same width. The other option is specification of the range of class boundaries, e.g. VarArrayOf([5,10,20,30,40,50]).

Parameter OPTIONS can be used for various adjustments of distribution or chart:

Multiple options can be passed to the function, individual options are separated by semicolon.

EXAMPLE:

BOUNDS=LEFTSIDE;FULLRANGE=NO

In the example project there are several sample plots with diameter at breast height for all trees. The aim is to present diameter distribution in user defined classes for all trees together and for individual tree species.

var tbSpecies,tbTrees :TTableWrapper;   
              
begin      
  tbSpecies := 
    Project.GetQueryResult(format( 'SELECT DISTINCT '
                                  +'Trees.Species,qspecies.Value1 AS Species_lkp '
                                  +'FROM Trees '
                                  +'INNER JOIN qspecies '
                                  +'ON Trees.Species = qspecies.ID '
                                  +'ORDER BY Trees.Species',
                                  [Plots.ValueAsinteger['ID']]));
  try           
    //overall distribution
    tbTrees := 
      Project.GetQueryResult( 'SELECT CAST(DBH_mm AS FLOAT)/10 AS DBH_cm '
                             +'FROM Trees '
                             +'WHERE Trees.IntactSnag=11 '
                             +'AND Trees.AliveDead=11 '
                             +'AND Trees.IndShtCop=10');
    try                
      ShowDistributionChart( tbTrees,
                             'DBH_cm',
                             false,
                             VarArrayOf([5,10,20,30,40,50,60,70,80,90,100,110]),
                             'DBH,cm',
                             'All species',
                             'BOUNDS=LEFTSIDE;FULLRANGE=NO');  
    finally
      tbTrees.Free;
    end;

    //diameter distribution by species 
    tbSpecies.First;                    
    while not tbSpecies.EOF do begin     

      tbTrees := 
        Project.GetQueryResult(format('SELECT CAST(DBH_mm AS FLOAT)/10 AS DBH_cm '
                                      +'FROM Trees '
                                      +'WHERE Species=%d '
                                      +'AND Trees.IntactSnag=11 '
                                      +'AND Trees.AliveDead=11 '
                                      +'AND Trees.IndShtCop=10',
                                      [tbSpecies.ValueAsInteger['Species']]));
      try                                                                          
        ShowDistributionChart( tbTrees,
                               'DBH_cm',
                               false,
                               VarArrayOf([5,10,20,30,40,50,60,70,80,90,100,110]),
                               'DBH,cm',
                               format('Species: %s',[tbSpecies['Species_lkp']]),
                               'BOUNDS=LEFTSIDE;FULLRANGE=NO');  
      finally
        tbTrees.Free;
      end;
      tbSpecies.Next;
    end;

  finally
    tbSpecies.Free;
  end;
  
end.                                                

See also:

Working with Field-Map data - scan and locate table records; Handling exceptions; Working with Field-Map data - using SQL queries; Parameterize regression models; Show diameter distribution; Grouping species; Working with Log window; Management of screen interface