2. Angular Misclosure

Angular misclosure is the difference between the measured angles' sum on a traverse and the angle condition for the traverse configuration.
The amount of allowable angular misclosure is dependant on the survey purpose. The limits are generally expressed as an Error of a Series:

img4    Eqn (B-4) 
C: Allowable misclosure, seconds
k: expected error in each angle, seconds
n: number of angles

 

Traditional formal standards from the FGCS Standards and Specifications for Geodetic Control Networks are:

Table B-1
Angular Misclosure
Order Class k (sec)
First - 1.7
Second I 3.0
  II 4.5
Third I 10.0
  II 12.0

 

Example

What is the allowable angular misclosure for a five-sided traverse if it is to meet Second Order Class II standards, Figure B-5?

b9
Figure B-5
Allowable Misclosure 

 

From Table 1, k = 4.5". Substituting into Eqn (B-4):

img5

Because this is a five-sided loop traverse, using Eqn (B-1) the angles should sum to:

img6

Therefore, the total should be in the range 539°59'50" to 540°00'10".

 

Informal standards can be created which reflect equipment, experience, conditions, project needs, etc.

Example

A control network is to be established for a construction project. Sight distances will be relatively short (under 300 ft) so measuring angles consistently will be a challenge. Testing under these conditions, our survey crew was able to measure an angle to a consistency of ±0°00'12". For this project, we will use an allowable misclosure of:

img7