We will solve one of the major mistakes during the leveling survey. That is missing entries in the Field Book. I hope this blog post helps you. many people ask me how if we missed the entry of survey data in the field book we solve the calculation after the completion of the Levelling survey.
What are the major data of the leveling survey?
If you are a surveyor, I know you have the technical terms of the survey, like the Field book, Foresight, backsight, Reduced Level, and more.
If you are interested in individual technical survey terms you can check the previous posts on my website. I have mentioned all the terms used in the leveling survey.
During the leveling survey, You must have foresight, backsight, Intermediate sight, Rise, Fall, height of the instrument, and a Reduced level reading.
Without these readings leveling survey is not clear. But if you missed the cross-sign data at the filled book table, I will help you with that. How to calculate the missing entries in the Field Book.
How to verify the data is accurate?
The accurate and precise data is only one field data. So as possible, you don’t miss all the data during the leveling survey. But, in the leveling survey, You have one chance to verify the data is accurate.
You know Airthematic Check? After calculating the data from the field book you can verify the calculation by the airthematic check process.
Keep in mind the following formula for Airthematic check.
ΣBS-ΣFS=LRL – FRL=ΣRise-ΣFall
This is a simple and easy way to solve the missing entries in the Field Book data of the leveling survey.
What are the Missing Entries in the Field Book sample?
Now We have one sample of Missing entries in the field book. How to find that particular data? You can see below:
| Station | BS | IS | FS | Rise | Fall | RL | Remarks |
| A | 2.285 | | | | | 232.460 | BM 1 |
| B | 1.650 | | x | 0.020 | | ||
| C | | 2.105 | | | x | | |
| D | x | 1.960 | x | | |||
| E | 2.050 | | 1.925 | | 0.300 | ||
| F | x | x | 232.255 | BM 2 | |||
| G | 1.690 | x | 0.340 | | | | |
| H | 2.865 | | 2.100 | | x | ||
| I | x | x | 233.425 | BM 3 |
Calculation of all Reduce Level and Missing data using the rise and fall method,
How to calculate missing data?
The following steps are the calculation part of this topic. By following the steps to calculate your missing data in the filed book. But on the list, you have given data in the filed book.
Foresight of station B (FS)=2.285-0.020=2.265 ( i.e BS-rise=FS)
Fall of station C (Fall)=1.650-2.105=-0.455 (i.e BS-IS=Fall)
Rise of Station D (Rise)=2.105-1.960=0.145
Backsight of station D (BS)= 1.925+(-0.300)=1.625
I hope you understand till here. Now we have one complicated issue. That is we don’t have two values of station F. We need two values i.e. IS and Rise of station F. For that, we need to Reduce the level (RL) of station E. If we have RL of E then we can easily find out the value of F station.
So let us find out the RL of station E. Using the Rise and fall method,
| Station | BS | IS | FS | Rise | Fall | RL | Remarks |
| A | 2.285 | | | | | 232.460 | BM 1 |
| B | 1.650 | | 2.265 | 0.020 | | 232.480 | |
| C | | 2.105 | | | 0.455 | 232.025 | |
| D | 1.625 | | 1.960 | 0.145 | 232.170 | | |
| E | 2.050 | | 1.925 | | 0.300 | 231.870 | |
| F | x | | x | 232.255 | BM 2 | ||
| G | 1.690 | | x | 0.340 | | | |
| H | 2.865 | | 2.100 | | x | | |
| I | | | x | x | | 233.425 | BM 3 |
Rise of Station F (Rise)=232.255-231.87=0.385
The intermediate sight of station F (IS)=2.050-0.385=1.665
Foresight of station G (FS)=1.665-0.340=1.325
Fall of Station H (fall)=1.325-2.100=-0.775
Again we need two values of station I. i.e. Foresight and Rise. Now we go to the Reduce level. we require a reduced level of station H for finding station I value.
| Station | BS | IS | FS | Rise | Fall | RL | Remarks |
| A | 2.285 | | | | | 232.460 | BM 1 |
| B | 1.650 | | 2.265 | 0.020 | | | |
| C | | 2.105 | | | 0.455 | | |
| D | 1.625 | | 1.960 | 0.145 | | | |
| E | 2.050 | | 1.925 | | 0.300 | ||
| F | 1.665 | | 0.385 | 232.255 | BM 2 | ||
| G | 1.690 | | 1.325 | 0.340 | | 232.595 | |
| H | 2.865 | | 2.100 | | 0.410 | 232.185 | |
| I | | | x | x | | 233.425 | BM 3 |
Rise of Station I (Rise)=233.425-231.820=1.605
Foresight of station I (FS)=2.865-1.605=1.260
| Station | BS | IS | FS | Rise | Fall | RL | Remarks |
| A | 2.285 | | | | | 232.460 | BM 1 |
| B | 1.650 | | 2.265 | 0.020 | | | |
| C | | 2.105 | | | 0.455 | | |
| D | 1.625 | | 1.960 | 0.145 | | | |
| E | 2.050 | | 1.925 | | 0.300 | ||
| F | 1.665 | | 0.385 | 232.255 | BM 2 | ||
| G | 1.690 | | 1.325 | 0.340 | | | |
| H | 2.865 | | 2.100 | | 0.410 | | |
| I | | | 1.280 | 1.585 | | 233.425 | BM 3 |
Summarize the answer
Following are the calculation of the required value and Reduced level of all stations.
| Station | BS | IS | FS | Rise | Fall | RL | Remarks |
| A | 2.285 | | | | | 232.460 | BM 1 |
| B | 1.650 | | 2.265 | 0.020 | | 232.480 | |
| C | | 2.105 | | | 0.455 | 232.025 | |
| D | 1.625 | | 1.960 | 0.145 | 232.170 | | |
| E | 2.050 | | 1.925 | | 0.300 | 231.870 | |
| F | 1.665 | | 0.385 | 232.255 | BM 2 | ||
| G | 1.690 | | 1.325 | 0.340 | | 232.595 | |
| H | 2.865 | | 2.100 | | 0.410 | 232.185 | |
| I | | | 1.280 | 1.585 | | 233.770 | BM 3 |
Airthematic Check
ΣBS-ΣFS=LRL – FRL=ΣRise-ΣFall
Formula,
ΣBS-ΣFS=12.165-10.855=1.31
LRL – FRL=233.770-232.46=1.31
ΣRise-ΣFall=2.475-1.165=1.31
Finally, our calculation is correct.
ΣBS-ΣFS=LRL – FRL=ΣRise-ΣFall (verified)
I am sure you are clear about this calculation. Don’t worry if you have missing leveling survey data due to different issues. If you have general data then you will be successfully calculated the missing entries in the field book.