An error is a mistake or shortcoming that happens during the survey process leading to wrong measurements. It is sometimes called discrepancies. The following are the type of errors or discrepancies in chain surveying.
Sources of Errors in Chain Survey and Their Correction
The errors can be divided into three groups:
- Cumulative (systematic) errors
- Compensating (accidental) errors
- Gross Errors
Cumulative errors are said to be systematic errors as they are one-directional hence keep on accumulating as the survey progresses. If not checked they have serious implications to the accuracy of the survey. Errors in this class include incorrect length of the tape, page of the tape or the tape not being in line. Since the sources of these errors are known, they can be eliminated. They can either be positive or negative errors. While positive errors shortens the measurement (e.g. where the tape length is shorter than what it should be) while negative errors elongates the measurements (e.g. where the tape is longer than what it should be). Checking the equipment can eliminate these errors.
Compensating errors are said to be accidental errors hence cancel out and does not pose serious problem to the accuracy of the survey. They arise as a result of not being perfect in the use of the equipment or in the whole survey process. For example, if the pull exerted on the tape in either more than or less than what should be the case, faulty results be gotten. The effect can either be positive or negative.
Gross Errors :
These are mistakes that can be attributed to the inexperience of the team leaders. These are very serious errors which although are random in accordance may lead to faulty plans and maps if not checked. They include discontinuing the chain length (e..g where some arrows are cost or misplaced); misreading of the tape; reading tape upside down (e.g. taking 6 to be 9), etc. By taking the necessary precautions, these errors can be corrected.
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