Select the INCORRECT obstacle in chaining in a chain survey.

Question

Prepp Team · Accepted Answer

Understanding Obstacles in Chain Surveying

Chain surveying is a fundamental surveying method used for measuring distances. During the process, surveyors often encounter various obstacles that can hinder either the process of chaining (measuring distances with a chain or tape), ranging (setting out intermediate points in a straight line), or both. Identifying the nature of these obstacles is crucial for selecting the appropriate method to overcome them and ensure the accuracy of the survey.

Types of Obstacles in Chain Surveying Field Work

Obstacles encountered during the actual field work of a chain survey can be broadly classified based on how they affect chaining and ranging:

Obstacle to Ranging Only: In this scenario, the two end points of the survey line are visible from each other, allowing chaining to be done around the obstacle, but intermediate points cannot be set out along the line due to the obstruction of the line of sight.
Obstacle to Chaining Only: Here, the end points of the line are not visible from each other directly, but ranging might be possible. The main issue is that the distance cannot be measured directly along the line because of a physical barrier.
Obstacle to Both Chaining and Ranging: This is the most restrictive obstacle, where neither the end points are visible from each other, nor can chaining be performed directly along the line.

Analyzing the Given Options

Let's examine each option provided in the context of obstacles encountered during chain surveying:

Obstacle to ranging only: This is a genuine type of obstacle encountered in the field during chaining, such as a hill or rising ground between two points. While chaining around or over is possible, direct ranging along the line is blocked.
Obstacle to chaining only: This is also a recognized type of field obstacle in chain surveying, like a pond or a river. The line of sight may be clear or can be made clear, but the physical barrier prevents direct measurement. Indirect methods are used to determine the distance.
Obstacle to both chaining and ranging: This represents obstacles such as buildings or dense woods, which block both the line of sight (preventing ranging) and physical access along the line (preventing direct chaining). More complex methods are needed to overcome these.
Obstacle to plotting: Plotting is the process of drawing the surveyed area on paper or in digital form based on the field measurements. This is typically done in the office after the field work is completed. An obstacle to plotting would relate to issues with the map or the drawing process itself, not an obstruction encountered during the physical act of surveying in the field (chaining and ranging). Therefore, it is not an obstacle in the context of the field operations of a chain survey.

Based on the analysis, obstacles to ranging only, chaining only, and both chaining and ranging are types of challenges faced during the fieldwork of a chain survey. An obstacle to plotting, however, is an issue related to the office work (mapping) and is not encountered during the actual process of measuring distances and setting out lines in the field.

The question asks for the INCORRECT obstacle in chaining in a chain survey. Out of the given options, the obstacle to plotting is the one that does not represent a problem encountered during the actual field work (chaining and ranging) phase of a chain survey.

Type of Obstacle	Affects Ranging?	Affects Chaining?	Example
Obstacle to Ranging Only	Yes	No (chaining possible indirectly)	Hill, rising ground
Obstacle to Chaining Only	No (or can be managed)	Yes	Pond, river
Obstacle to Both Chaining and Ranging	Yes	Yes	Building, dense forest
Obstacle to Plotting	Not a field obstacle in chain surveying		Issues with drawing, map scale

Conclusion

The options related to obstacles affecting ranging and/or chaining are genuine challenges encountered during the field portion of a chain survey. The obstacle to plotting is an issue related to the office work (mapping) and is therefore not an obstacle encountered during the chaining phase in the field. Thus, 'Obstacle to plotting' is the incorrect option as a type of obstacle in chaining during a chain survey.

Revision Table: Chain Survey Field Obstacles

Obstacle Type	Description	Impact
Ranging Only	Line of sight is blocked, but direct physical access is possible.	Cannot align intermediate points directly; chaining done indirectly around or over.
Chaining Only	Physical barrier prevents direct measurement, but line of sight exists or can be established.	Cannot measure distance directly along the line; distance found using indirect methods.
Both Chaining and Ranging	Both line of sight and physical access are blocked along the survey line.	Requires setting up offset lines or using other survey techniques to determine position and distance.

Additional Information: Chain Surveying Basics and Challenges

Chain surveying is the simplest form of surveying, suitable for small, relatively flat areas. It relies on linear measurements taken with a chain or tape. The accuracy of a chain survey depends heavily on careful field work, including accurate measurement of distances and proper handling of obstacles. Common errors in chain surveying can arise from various sources:

Instrument Errors: Faulty chain or tape (wrong length, kinks, etc.).
Personal Errors: Carelessness in holding the chain, ranging, or reading measurements.
Natural Errors: Variations in temperature affecting the chain length, strong winds, ground irregularities, and, importantly, natural obstacles like rivers, hills, buildings, etc.

Overcoming obstacles is a critical skill in chain surveying. Various geometrical methods, such as constructing triangles or setting up perpendiculars, are employed to measure distances indirectly when direct measurement is impossible. These methods ensure that the survey line can be established or its length determined accurately despite the physical obstruction.