#include<bits/stdc++.h>
#define MAX 200
#define inf 1<<29
#define linf 1e18
#define eps (1e-8)
#define mod 1000000007
#define pi M_PI
#define f first
#define s second
#define mp make_pair
#define pb push_back
#define all(a) (a).begin(),(a).end()
#define pd(a) printf("%.10f\n",(double)(a))
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define RFOR(i,a,b) for(int i=(a)-1;(b)<=i;i--)
#define equals(a,b) (fabs((a)-(b))<eps)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<double,int> pdi;
typedef vector<int> vi;
typedef vector<pii> vpi;
const int dx[8]={1,0,-1,0,1,1,-1,-1};
const int dy[8]={0,1,0,-1,1,-1,1,-1};

class Point{
public:
  double x,y;
  Point(double x=0,double y=0):x(x),y(y){}

  Point operator+(Point p){ return Point(x+p.x,y+p.y);}
  Point operator-(Point p){ return Point(x-p.x,y-p.y);}
  Point operator*(double k){ return Point(x*k,y*k);}
  Point operator/(double k){ return Point(x/k,y/k);}
  bool operator<(Point p)const{ return (x!=p.x ? x<p.x : y<p.y);}
  bool operator==(Point p)const{ return fabs(x-p.x)<eps && fabs(y-p.y)<eps;}

  double abs(){ return sqrt(norm());}
  double norm(){ return (x*x+y*y);}
};
typedef Point Vector;
typedef vector<Point> Polygon;

class Segment{
public:
  Point p1,p2;
  Segment(Point p1=Point(),Point p2=Point()):p1(p1),p2(p2){}
  bool operator==(Segment s){ 
    if(p1==s.p1 && p2==s.p2)return true;
    if(p1==s.p2 && p2==s.p1)return true;
    return false;
  }
};
typedef Segment Line;

double norm(Vector a){ return (a.x*a.x+a.y*a.y);}
double abs(Vector a){ return sqrt(norm(a));}
double dot(Vector a,Vector b){ return (a.x*b.x+a.y*b.y);}
double cross(Vector a,Vector b){ return (a.x*b.y-a.y*b.x);}

bool isParallel(Vector a,Vector b){
  return equals(cross(a,b),0.0);
}

bool isParallel(Segment s,Segment t){
  return equals(cross(s.p1-s.p2,t.p1-t.p2),0.0);
}

Point project(Segment s,Point p){
  Vector base=(s.p2-s.p1);
  double r=(dot(p-s.p1,base)/base.norm());
  return (s.p1+base*r);
}

Point reflect(Segment s,Point p){
  return p+(project(s,p)-p)*2;
}

int ccw(Point p0,Point p1,Point p2){
  Vector a=p1-p0;
  Vector b=p2-p0;
  if(cross(a,b)>eps)return 1;
  if(cross(a,b)<-eps)return -1;
  if(dot(a,b)<-eps)return 2;
  if(a.norm()<b.norm())return -2;
  return 0;
}

bool intersect(Point p1,Point p2,Point p3,Point p4){
  return (ccw(p1,p2,p3)*ccw(p1,p2,p4)<=0 &&
          ccw(p3,p4,p1)*ccw(p3,p4,p2)<=0);
}

bool intersect(Segment s1,Segment s2){
  return intersect(s1.p1,s1.p2,s2.p1,s2.p2);
}

Point getCrossPointLL(Line a,Line b){
  double A=cross(a.p2-a.p1,b.p2-b.p1);
  double B=cross(a.p2-a.p1,a.p2-b.p1);
  if(abs(A)<eps || abs(B)<eps)return b.p1;
  return b.p1+(b.p2-b.p1)*(B/A);
}

int contains(Polygon g,Point p){
  int n=g.size();
  bool x=false;
  for(int i=0;i<n;i++){
    Vector a=g[i]-p,b=g[(i+1)%n]-p;
    if(abs(cross(a,b))<eps && dot(a,b)<eps)return 1;
    if(a.y>b.y)swap(a,b);
    if(a.y<eps && eps<b.y && cross(a,b)>eps)x=!x;
  }
  if(x)return 2;
  return 0;
}

Polygon reflect(Polygon p,Line L){
  Polygon res;
  for(int i=0;i<p.size();i++)res.push_back(reflect(L,p[i]));
  reverse(res.begin(),res.end());
  return res;
}

vector<Point> unique(vector<Point> vp){
  sort(vp.begin(),vp.end());
  vector<Point> res;
  res.push_back(vp[0]);
  for(int i=1;i<vp.size();i++){
    if(!(vp[i]==res.back()))res.push_back(vp[i]);
  }
  return res;
}

int n;
Polygon buildings[100];
Point s,t,rs,rt;
Line L;
vector<pdi> e[MAX];
Polygon p1,p2;
vector<Point> vp;

void init(){
  FOR(i,0,n)buildings[i].clear();
  vp.clear();
  p1.clear();
  p2.clear();
  FOR(i,0,MAX)e[i].clear();
}

void add_edge(int from,int to,double cost){
  e[from].pb(mp(cost,to));
  e[to].pb(mp(cost,from));
}

bool check(Point a,Point b){
  Segment s1=Segment(a,b);
  FOR(i,0,p1.size()){
    Segment s2=Segment(p1[i],p1[(i+1)%p1.size()]);
    if(isParallel(s1,s2))continue;
    if(intersect(s1,s2)){
      Point c=getCrossPointLL(s1,s2);
      if(!(c==a) && !(c==b))return false;
    }
  }
  FOR(i,0,p2.size()){
    Segment s2=Segment(p2[i],p2[(i+1)%p2.size()]);
    if(isParallel(s1,s2))continue;
    if(intersect(s1,s2)){
      Point c=getCrossPointLL(s1,s2);
      if(!(c==a) && !(c==b))return false;
    }
  }
  Point m=a+(b-a)/2;
  if(contains(p1,m)==0)return false;
  if(contains(p2,m)==0)return false;
  return true;
}

double dijkstra(int s,int t){
  double d[MAX];
  fill(d,d+MAX,inf);
  priority_queue<pdi,vector<pdi>,greater<pdi> > pq;
  pq.push(mp(0,s));
  d[s]=0;

  while(pq.size()){
    pdi u=pq.top();
    pq.pop();
    if(d[u.s]<u.f)continue;
    if(u.s==t)return u.f;

    FOR(i,0,e[u.s].size()){
      pdi next=e[u.s][i];
      if(d[u.s]+next.f<d[next.s]){
        d[next.s]=d[u.s]+next.f;
        pq.push(mp(d[next.s],next.s));
      }
    }
  }
  return -1;
}

double solve(){
  rs=reflect(L,s);
  rt=reflect(L,t);
  FOR(i,0,n){
    if(contains(buildings[i],s)!=0 &&
       contains(buildings[i],t)!=0 )p1=buildings[i];
    if(contains(buildings[i],rs)!=0 && 
       contains(buildings[i],rt)!=0 )p2=buildings[i];
  }
  if(p2.size()==0)return -1;
  p2=reflect(p2,L);
  FOR(i,0,p1.size())vp.pb(p1[i]);
  FOR(i,0,p2.size())if(contains(p1,p2[i])!=0)vp.pb(p2[i]);
  vp=unique(vp);
  vp.pb(s);
  vp.pb(t);
  FOR(i,0,vp.size()){
    FOR(j,i+1,vp.size()){
      if(check(vp[i],vp[j]))add_edge(i,j,abs(vp[i]-vp[j]));
    }
  }
  return dijkstra(vp.size()-2,vp.size()-1);
}

int main()
{
  while(1){
    cin>>n;
    if(n==0)break;
    init();
    FOR(i,0,n){
      int m;
      Polygon p;
      cin>>m;
      FOR(j,0,m){
        int x,y;
        cin>>x>>y;
        p.pb(Point(x,y));
      }
      buildings[i]=p;
    }
    cin>>s.x>>s.y>>t.x>>t.y;
    cin>>L.p1.x>>L.p1.y>>L.p2.x>>L.p2.y;
    double ans=solve();
    if(ans==-1)cout<<"impossible"<<endl;
    else pd(ans);
  }
  return 0;
}

Measured memory_bytes: 3280