ArcGIS python 椭球面积

###验证=========
import arcpy
class ToolValidator(object):
  """Class for validating a tool's parameter values and controlling
  the behavior of the tool's dialog."""

  def __init__(self):
    """Setup arcpy and the list of tool parameters."""
    self.params = arcpy.GetParameterInfo()

  def initializeParameters(self):
    """Refine the properties of a tool's parameters.  This method is
    called when the tool is opened."""
    return

  def updateParameters(self):
    if self.params[0].value:
        inFeature = self.params[0].value
        try:
            fieldList = arcpy.ListFields(inFeature)
            fList = []
            for field in fieldList:
                if field.type=="Double" and field.editable:
                    fList.append(field.name)

            self.params[1].filter.list = fList

            if self.params[1].altered:
                if len(fList)>0 and self.params[1].value=="":
                    self.params[1].value= fList[0]


        except Exception,e:
            print e.message();
        return

  def updateMessages(self):
    """Modify the messages created by internal validation for each tool
    parameter.  This method is called after internal validation."""
    return