This is part two of a long-term series that will cover many features of the cave survey application, Walls Project Editor. To start at part one, click here.

 What do I need for the tutorial?

• Windows PC (macOS users can try running Walls using Boot Camp or an application such as Wine).

• Walls Project Editor, available for free, here.

• A Walls project file as created in part one of this series, here.

Walls Tutorial:
CONNECTING CIRCUITS

• by Rory O’Keefe, January 27, 2021

A quick note:

The first three sections of this tutorial are focused on adding new data to the project created in Part One: Entering Dive Survey. If you already have a Walls project with circuits, skip to Section 4 for tips on evaluating your data.

Section 1: Enter new data into your existing project.

Note that detailed instructions for the following steps have already been covered in Part One: Entering Dive Survey. Please refer back to part one for additional explanations if needed.

Part 1: Open the Walls project.

1. Open the Walls project file created in the previous tutorial.

   • The project file name used in part one was Survey Down Database.

   • Walls projects are saved as WPJ files.

Part 2: Create a new book under your project tree.

1. Create a new book with the title of Dos Palmas under the main project book, and use DOSPAL as the file name (Dos Palmas is the name of this tutorial’s cave entrance).

   • The Geographical Reference settings can be left as Inherited because this new cave entrance is less than 40 kilometers from the main project’s reference location.

   • For step-by-step instructions, go to Section 4 of Part One: Entering Dive Survey.

Part 3: Create a new survey file.

1. Create a new survey file within the Dos Palmas book.

   • Write Mainline Upstream as the file title, and DOSPAL1 as the file name.

   • Tip: For organizational purposes, I use consecutive file names for the SRV files, such as DOSPAL1, DOSPAL2, DOSPAL3, etc so that they are easy to locate and share with teammates.

   • For step-by-step instructions, go to Section 5 of Part One: Entering Dive Survey.

Part 4: Enter the data.

1. Copy the data as shown below into the new survey file and select Compile to save.

• Note that the entrance coordinates of the cave are included in the data header.

• For step-by-step instructions, read Sections 6-7 of Part One: Entering Dive Survey.

Part 5: View the compiled data.

1. Navigate to the Map tab of the Review box and confirm that the line survey looks correct. It should be one continuous line.

2. Working in the Map tab, under the Stations column, select Label and Mark, then Display Map.

   • This will add a + symbol and name tag to each station along the line survey which will help identify the correct station name.

   • Zoom in so that every station is clearly labeled.

3. Leave the map open and proceed to the next section.

Section 2: Find the connecting station names.

Line surveys are connected through their station names during data entry. This step uses your survey notes and knowledge of the cave to locate the most likely connecting station. You can then compare your reference shots with the original data to confirm the exact station.

Take a moment to look at the following sketch for a basic understanding of what was surveyed and where the circuit should connect to the mainline.

Part 1: View the map to locate the approximate station names.

Based on the memory-sketch above, you can expect the circuit line to connect between the first permanent station of the mainline and the upstream station which is marked by the third permanent arrow. The mainline also abruptly turns to the west at this upstream station, which is a useful identifier.

1. Look at the displayed map in Walls and make an educated guess as to which station names are the most likely connecting stations.

   • I used a primary reel to connect the GPS station with the mainline, and so the first two shots are not part of the permanent guideline. This means that Station DOP3 is most likely the first permanent station of the mainline.

   • The second connecting station was located at a hard corner west which looks to be Station DOP14.

Part 2: Read the data to confirm the stations.

Scroll to the above stations in your survey file to confirm they are correct by comparing the data of your reference shots* and comments. Note that reference shots are not used in this example.

1. Double-click the survey file, Mainline Upstream, in the project-tree window to view the survey data.

2. Looking at the data line to Station DOP3, the comment says, “Cave line begins. Jump line to NW.”

   • You are expecting the circuit line to connect to the start of the cave line from the north-west. This coincides with the comment which means that DOP3 is likely the correct station.

   • The data line above DOP3 states that DOP1 to DOP2 is a “Temporary line from GPS to cave line.” This also confirms that DOP3 is the correct station as DOP1 and DOP2 were made by a temporary guideline (the primary reel).

3. Looking at the data line to Station DOP14, the comment says, “Red Arrow, jump line visible to E.”

   • You are expecting the circuit line to connect at the third permanent arrow upstream from the east. This coincides with the comment which means that DOP14 is likely the correct upstream station.

*Reference Shot: An overlapping survey of a line you have already surveyed. Multiple reference shots are normally taken at each end of a circuit so that the new data can be compared with the previous data. If the distances, azimuths, and depths are the same for both sets, you can confidently say that the circuit is connected to the correct stations.

Station DOP3 and DOP14 will therefore be the first and last station names of the circuit line.

Section 3: Enter the circuit data.

Part 1: Create a new survey file.

1. Create a new survey file within the Dos Palmas book.

   • Write Entrance Circuit as the file title and DOSPAL2 as the file name.

Part 2: Enter the data.

1. Copy the data as shown below into the new survey file and select Compile to save.

   • The entrance coordinates are not included in the header comments for this survey because the new data will be attached to the previous survey through the connecting station names.

   • Note that the ;Section and #Date lines have been updated from the Mainline Upstream file - forgetting to change the date is a common error when copy & pasting the header.

   • Pay attention to the station names and note how the connecting stations, DOP3 and DOP14, have been used to create a circuit.

Part 3: View the compiled data.

1. Navigate to the Map tab of the Review box and confirm that the line survey looks correct. Compiling only the Entrance Circuit file should give you one continuous line totaling 95.4 m / 313 ft.

Section 4: Evaluating the circuit.

Walls offers a number of useful tools to evaluate the accuracy of a circuit, such as the ability to view the corrected and uncorrected line survey on the same map, a table that identifies the most likely errors, the horizontal loop distance, and the horizontal error distance.

Part 1: Compile the project.

1. Start by selecting the Dos Palmas book, as you are now compiling the complete project rather than the individual survey files, and then select Compile / Review.

   • The Compile button automatically becomes a Review button if the project has already been compiled. You can also right-click the book and select Recompile Item.

2. If your compiled map does not look like the image below, please recheck your survey file for typos.

   • Remember to recompile the project after making any changes to the survey file.

Part 2: The Geometry tab.

The Geometry tab acts as a statistics page for your survey project. From here you can view the total number of stations, the cave length, number of circuits, and loop closure ratios of each circuit.

It is also the starting point to tracking down survey errors and determining which traverses need correcting.

Take a moment to look at the following image for a quick rundown of the information displayed within the Geometry tab.

Part 3: Looking at loops.

Unlike other survey programs such as Compass or Ariane’s Line, Walls does not provide you with a loop closure percentage but uses a ranking method for each individual traverse or loop system.

This ranking system, shown as F/UveH and F/UveV values in the Geometry tab, can be used to selectively detach (or float) the lowest-accuracy traverses from a loop system to prevent them from having a negative influence over the higher-grade survey.

How these F/UVE statistics are calculated are well defined in the Statistical Formulas section of the Walls User Manual, so I will focus on the basic methods of using these numbers to evaluate dive survey.

The definitions:

F: An F-ratio that measures the disagreement between a given observation and a larger set of potentially conflicting data. A value greater than one indicates that overall consistency will improve if the observation is discarded. A value less than one means it would worsen.

UVE: Unit Variance Estimate, is a computed byproduct of a least-squares adjustment, and should have a value close to one when the number of loops in a network is sufficiently large. UveH is for the horizontal, UveV is the vertical.

The Walls manual states that an overall UVE of less than 2.0 should be your goal for a large project. However, this refers to dry cave survey, and in my experience, underwater survey is rarely this accurate due to the limited equipment divers have available to them.

So, I aim for a starting UveH of less than 10 for a large underwater project, however, a total UveH of less than 5 is ideal, with the UveV being less than 2. (Depths can be more accurately recorded underwater than the horizontal measurements).

The following steps highlight the process that I use to evaluate underwater circuits:

1. Working in the Geometry tab, select the Loop System or Isolated Loop you would like to evaluate.

   • A Loop System is a collection of multiple connecting circuits within a large project.

   • An Isolated Loop is an individual circuit.

   • As there are no Loop Systems in this project, you will find the tutorial circuit under the Isolated Loops column.

2. Next, look at the Traverse column, for a list of individual traverses (end-to-end connections), within the selected Loop System.

   • Here you can see that the current ranking of the traverse is 7.8/0.00. This means that the F-ratio of this traverse is 7.8, and if it were floated the total system UveH would drop to 0.00. (If there were multiple loops this number would not be 0.00, but an averaged value based on the combined remaining F-ratios).

3. An F-ratio number of 0 is perfect, with 1 being close to perfect. This means that 7.8 is higher than I would like to see. I would therefore float this circuit and review the map to see if there is an obvious error, such as an odd angle or incorrect station name.

Part 4: Floating a loop.

1. With the tutorial circuit selected under the Traverses column, select the FloatH button below it.

2. Next, select the Map tab. You should now see two versions of the circuit line. The red line represents the corrected loop and the yellow line represents the uncorrected loop.

3. Working in the Map tab, under the Traverses column, click the Selected option.

   • This will allow both the corrected and uncorrected versions of the line survey to be viewable on the larger map.

4. Select Display Map and look for obvious errors.

   • Use the Measuring Tool to check the error distance by clicking and dragging between the gap of the uncorrected loop.

In this case, there appears to be multiple small cumulative errors rather than one major error. You could now decide to take one of the following actions:

• Leave the circuit as it is and accept the slightly lower accuracy.

• Keep the circuit floated to remove its influence on the projects total UVE - not recommended in this case as it is the only circuit of the project.

• Resurvey the section for better accuracy.

• Fix the data using the information available to you in the Traverse tab.

Part 5: The Traverse tab.

The Traverse tab helps to highlight potential typos or survey mistakes in a loop system. Navigating to the Traverse tab will display your selected traverse’s survey data next to the “best correction” numbers required to close the loop.

It also lists the total length of the selected loop and the horizontal error distance which can be used to calculate a rough accuracy percentage.

The following steps highlight the basic steps to using the Traverse tab:

1. First, select a traverse in the Geometry tab before navigating to the Traverse tab.

   • The Traverse tab will automatically load the data of your selected traverse.

   • You can scroll through the system traverses by selecting the << / >> buttons.

2. Looking at the table, you will see both the Original Vectors and data showing the Best Corrections.

   • The Original Vectors are the original distances, azimuths, and depths that you typed into the text-editor. Note that these numbers may be slightly different from what you originally typed as they are now corrected for magnetic declination, height adjustments, etc. The depths have also been converted into vertical degrees.

   • The Best Correction vectors are the adjustments needed to be applied in order to create a perfect loop. Note that only one line of the Best Correction table needs to be applied to fix the loop - not the entire list of corrections.

   • You will also note that some of the numbers in this table are red. Numbers are highlighted in red when only one of the three measurements (distance, azimuth, or the vertical angle) of a vector do not meet the tolerance limit. The default tolerance limit is a maximum of 1 meter for distance, 5 degrees for azimuth, and 5 degrees for the vertical angle. This indicates a likely survey error and these numbers should be checked with the original data for typos.

3. You can use this information to pinpoint the most likely survey error that is preventing a loop from closing.

   • In most cases, it is a single measurement that causes a loop failure.

   • Numbers highlighted in red are the most likely errors as they have been singled out as the only bad measurement from the vector.

4. Finally, you can calculate a loop closure percentage based on the total horizontal length of error, divided by the horizontal length of a loop.

   • In this case, the circuit is 223.8 meters long, and the horizontal error is 3.3 meters.

     • 3.3 / 223.8 = 0.0147

     • 0.0147 x 100 = 1.47%

Conclusion

Walls admittedly has a learning curve, but it is an excellent tool for managing large amounts of data, archiving, and cave mapping. It is my personal program of choice for working with survey data and I can say through experience that it offers the necessary features to take you straight through to a finished map.

It is also worth noting that Walls includes an extremely thorough user manual with a well-indexed search function.

View the image below for instructions on how to access the Walls manual: