“Show candidates” option

This option helps you to spread height measurements equally across the entire DBH range on the plot. You can choose whether you want to see candidates for one species or for all species on the plot by selecting the appropriate species from the list. The list of candidates has three columns:

1. DBH size class

2. Candidates for height measurement – tree IDs sorted by DBH classes

3. Measured - number of trees already measured in each individual DBH classes


The selection of the height candidates for the height curve follows the idea that it is necessary to measure at least four heights (absolute technical minimum for the height curve parameterization) equally distributed along the range of the DBH. Field-Map uses following algorithm and height measurement support functionality:


  1. .Min and max of DBH of the species is found in the database (Dmin,Dmax)


  1. Quadratic mean of DBH of the species is calculated (Dg)


  1. Size of the DBH class of the species is calculated: w=(Dmax-Dmin)/5


  1. Each tree of the species is classified based on its DBH in following order:

DBH>Dg+1.5w -> MAX

DBH>Dg+0.5w -> LARGE

DBH>Dg-0.5w -> MID

DBH>Dg-2w -> SMALL


  1. IDs of the trees in four size classes are listed, only trees without height measurement are included. On the right side of the table the number of already measured heights per size class is presented


  1. Those classes which do not have at least two measured heights are highlighted


  1. It is possible to leave invalid trees (e.g. broken or dead trees) out of the selection. For that there is the tree layer event Onlayer events/BeforeSelectHeightCandidates. Here it is possible to write a user script which marks the trees which should not be selected as the height measurement candidates. Such script can be written as follows:


var q :TTableWrapper;

   v :variant;

   n :integer;

begin

 q := Tree.GetQueryResult('ID','Status_2019 IN (1,3)'); {1-dead tree; 3-broken tree}

 try

   v := VarArrayCreate([0,q.RecordCount-1],varVariant);

   n := 0;

   q.First;

   while not q.EOF do begin

    v[n] := q['ID'];

     inc(n); 

     q.Next;

   end;

 finally

   q.Free;

 end;


{pass the information into height candidate selection}

 Globals.SetGlobalVariable('InvalidTreeIDs',v); 

end.


The conditions/algorithm of the tree selection can be fully adjusted according to the particular methodology and the database structure.


  1. Double click to the tree ID of height candidates table automatically select the tree in the list.


  1. Height curve can be visualized on the page DBH-H of the tree layer.

First measure all tree positions and download DBH. You can also measure a few heights at random.

  1. Switch to the Trees form
  2. Click on the DBH-H tab
  3. Enter the interval for DBH class into the “DBH class” edit box (default interval is 4 cm)
  4. Open Candidates  list 

a) Click the Show candidates button

b) Click the Show candidates button on Basic data tab - Candidates button




  1. A list of candidates appears showing IDs of trees to be measured and number of trees already measured in each “size class”
  2. Click Close to close the list of candidates and return to DBH-H form
  3. Or double click to the tree ID of height candidates to automatically select the tree in the list


Note: You should measure trees with id that are highlighted green