+ppA = [middia_use/2, 0];
+ppB = ppA + [0, 1] * htop;
+ppC = ppB + [-1,0] * wall;
+ppD = [ppC[0], ppA[1] - wall/slope];
+ppE = [india_use/2, ppD[1] - (india_use/2 - ppD[0])/slope];
+ppF = ppE + [0,-1] * (htop + hbot);
+ppG = ppF + [1, 0] * wall;
+ppK = [outdia/2, ppA[1]];
+ppJ = ppK + [0,-1] * wall;
+ppH = [ppG[0], ppJ[1] - (ppJ[0]-ppG[0])/slope];
+
+module Plan1() {