func (v *Viewport) IsSymbolTable() bool {
	return true
}
IsSymbolTable is for SymbolTable interface.
package table
import (
	"github.com/yofu/dxf/format"
	"github.com/yofu/dxf/handle"
)
type Viewport struct {
	handle        int
	owner         handle.Handler
	name          string  
	LowerLeft     []float64
	UpperRight    []float64
	ViewCenter    []float64
	SnapBase      []float64
	SnapSpacing   []float64
	GridSpacing   []float64
	ViewDirection []float64
	ViewTarget    []float64
	Height        float64
	AspectRatio   float64
	LensLength    float64
	FrontClip     float64
	BackClip      float64
	SnapAngle     float64
	TwistAngle    float64
}
func NewViewport(name string) *Viewport {
	v := &Viewport{
		name:          name,
		LowerLeft:     []float64{0.0, 0.0},
		UpperRight:    []float64{0.0, 0.0},
		ViewCenter:    []float64{0.0, 0.0},
		SnapBase:      []float64{0.0, 0.0},
		SnapSpacing:   []float64{0.0, 0.0},
		GridSpacing:   []float64{0.0, 0.0},
		ViewDirection: []float64{0.0, 0.0, 0.0},
		ViewTarget:    []float64{0.0, 0.0, 0.0},
		Height:        400.0,
		AspectRatio:   1.0,
		LensLength:    50.0,
		FrontClip:     0.0,
		BackClip:      0.0,
		SnapAngle:     0.0,
		TwistAngle:    0.0,
	}
	return v
}