Strength of Fix or Figure

The accuracy with which a plane table station can be located through three point problem is known as its fix. The degree of accuracy of solution of the three point problem is designated as its strength i.e., if the accuracy is high, the fix is termed as strong and for low accuracy, fix is called as poor. The accuracy of fix depends on the relative positions of the plotted points and that of location of the plane table station. Thus, the choice of plotted objects and location of table should be made to get a strong fix.

The strength of fix is good if

  • the location of station is chosen within the great triangle formed by joining the three well defined objects X;
  • the middle object is nearer to the position of the plane table than other two objects;
  • of the two interior angles subtended by the three objects at the plane table stations, one is small and the other is large. However, the objects subtending small angle should be widely separated to each other.

The strength of fix is poor if

  • The location of the plane table is on or near the circumference of the great circle.
  • Both the interior angles, subtended, by well defined objects, at the plane table stations, are small.

Figure 35.7 provides a pictorial representation of the quality of strength of figure with reference to the location of the three chosen objects

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