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This document is archived and information here might be outdated. Recommended version. |
IProportionalSymbolRenderer.ValueUnit Property (ArcObjects .NET 10.8 SDK)
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This document is archived and information here might be outdated. Recommended version. |
Units of the value field.
[Visual Basic .NET] Public Property ValueUnit As esriUnits
[C#] public esriUnits ValueUnit {get; set;}
[C++]
HRESULT get_ValueUnit(
esriUnits* unit
);
[C++]
HRESULT put_ValueUnit(
esriUnits unit
);
[C++] Parameters unit [out, retval]
unit is a parameter of type esriUnits* unit [in]
unit is a parameter of type esriUnits
This property specifies the real world distance units that the data in Field represent.
Known Units
If the data in Field represent an actual distance in the real world, and you know the units for the data, then you should set ValueUnit to these units. For example, for your tree point data you might have measured the radius of each tree canopy in meters and have this stored in the field "Canopy". In this scenario you should set ValueUnit = esriMeters and also set ValueRepresentation = esriValueRepRadius. See ValueRepresentation for more information about how symbols are scaled to data values. Also, in this case you do not need to set MinDataValue.
Unknown Units
If the data in Field does not represent an actual distance in the real world, then you should set ValueUnit = esriUnknownUnits. In this case you need to set MinDataValue to the data value corresponding to the size of the symbol set for MinSymbol.
In the marker symbol case, a feature with value that is twice the MinDataValue will have a symbol with an area twice as big as the MinSymbol. An assumption is made that the marker symbol is square for this calculation. Also, for marker symbols with unknown units, an appearance compensation factor can be applied by setting FlanneryCompensation = True. Empirical testing has shown that people tend to underestimate differences in area when visually comparing two marker symbols. Therefore, this factor increases the difference in area between a smaller symbol and a a larger symbol as the symbols get larger.
In the line symbol case, a feature with value that is twice the MinDataValue will have a width that is twice as wide as the MinSymbol.