Task

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Code

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Getting a pointer the IDU MapLayer

A pointer to the IDU MapLayer is passed in the EnvContext structure during each invocation of an interface. To access this pointer:

            
 const MapLayer *pLayer = pContext->pMapLayer;

Iterate over the IDU coverage and access data

Use a MapLayer::Iterator, in conjunction with the IDU's MapLayer::GetData() function, to retrieved teh current IDU data for a given field (column) in the database, as follows

            
 const MapLayer *pLayer = pContext->pMapLayer; 
 for ( MapLayer::Iterator idu=pLayer->Begin(); idu < pLayer->End(); idu++ ) 
     {
     float value; // int, CString, bool, etc.depending on col datatype 
     pLayer->GetData( idu, m_colOfInterest, value ); // do something with the idu’s value of the specified column 
     }

Iterate over the DeltaArray

DeltaArray’s provide a complete history of every change that has been made to the IDU coverage. Further, Envision tracks the last time each model/process has “seen” the DeltaArray. This means that if a model/process want to see anychanges that have been made either from a particular years, form the beginning of the run, or since it was last “seen” by the model/process, that is easily accessed as follows.

 DeltaArray *deltaArray = pContext->deltaArray;// get a ptr to the delta array
 INT_PTR daSize = deltaArray->GetSize();  // use static size so deltas added
      // by this process this cycle don’t
      // get looked at!!!
 // iterate through deltas added since last “seen”
 for ( int i=pContext->firstUnseenDelta; i < daSize; ++i )
    {
    DELTA &delta = deltaArray->GetAt(i);
    // do something with the delta
    }

Update data in the IDU layer

Models/Processes should not modify the map directly – instead, they should add a DELTA to the map indicating the change to be made. Envision then modifies the map with all DELTA’s added when the model/process returns control to Envision when exiting the call. The EnvContext contains a pointer to a function for adding DELTA’s. To simplify use, the EnvExtension class provides a member function makes it very easy to add DELTA’s.

 const MapLayer *pLayer = pContext->pMapLayer;
 
 for ( MapLayer::Iterator idu=pLayer->Begin(); idu < pLayer->End(); idu++ )
    {
    float fValue = 10.0f;
    int   iValue = 20;   
    UpdateIDU( pContext, idu, m_col0, fValue, ADD_DELTA ); // note: these are polymorphic
    UpdateIDU( pContext, idu, m_col1, ivalue, ADD_DELTA );
    }

Expose input/output variables

Models can optionally expose input and output variables to Envision. Exposed input variables can be set differently across different scenarios; exposed output variables are used by Envision to collect data from the model/process during a run. The EnvExtension parent class manages these variables. All that is needed is to call AddInputVar() and AddOutputVar() in either the model constructor or in your model's Init() method.

MyModel.h

 class MyModel : public EnvAutoProcess
 {
  protected:
    int m_input1;   // declare input, output variables
    float m_input2;
    int output;
 
 public:
    // constructor
    MyModel(); 
 }

MyModel.cpp

 MyModel::MyModel()
 : EnvEvalModel()
 , m_input1(10)
 , m_input2(2)
 , m_output( 5 )
    {
    //  Arguments are label, variable,  description
    AddInputVar ( _T(“Input 1”), m_input1, _T(“this is an input”) ); 
    AddInputVar ( _T(“Input 2”), m_input2, _T(“this is another”) ); 
    AddOutputVar( _T(“Output”),  m_output, _T(“this is an output”) ); 
    }