Interpretation tools

Interpretation tools work on both point cloud and on surface mesh data. All interpretation tools are available via the Interpretations tab in the Ribbon Bar. Interpretation tools fall into 3 categories:

• Structure
• Sedimentology
• Annotations

1. Structure Panel

This Structure Panel includes several methods of collecting structural information from a 3D outcrop. Below are the currently available 5 tools for structural measurements. There are several sub-menus for each tool, and are described below.

1. Planes (Dip Azimuth)
2. Faults
3. Scan Lines
4. Plunges
5. Polylines

Dip Azimuth (orientations or planes)

This tool will assign a new measurement to the selected type defined by the mode. This tool has 3 modes:

• Bedding
• Fracture
• Cleavage

Each mode contains different methods associated with the Dip Azimuth button to collection orientation information:

• 3 Points
• N Points
• 1 Point

No.	Type	Defintion	Usage
1.	3 Points	Default when Dip Azimuth is selected. A best-fit plane is created from 3 selcted points.	Click 3 points on the 3D model to calculate an orientation.
2.	N points	N-Points method allows n number of points to be digitised.	Click n number of points on the 3D model. Double click to end the digitisation and calculate the orientation. Equally, click + drag to automatically extract n points along the digitised trace.
3.	1 Point	1 Point method allows for a measurement to be manually entered into the model, such as a measurement taken in the field.	Click where the orientation data was collected and enter the associated Dip and Azimuth.

 

Polylines and Faults

Polylines and Faults share the same digitising modes and are executed in the same way.

This section describes the polyline digitising and editing facilities. Both Digitise Polyline and Digitise Fault have sub-menus of different methods to digitse the desired feature. After successful additiion of a Polyline or Fault, metadata may be added such as the Stratigraphy where the feature is located. The default option is New Polyline which allows you to create a new polyline.

Type	Defintion	Usage
Digitise Polyline	Creates a 3D polyline from digitised points	Points are digitised by individual clicks on the model, or click + drag to continually digitise*. Double click ends digitisation. Single click digitising is default behaviour.
Digitse Fault	Creates a 3D polyline from the digitised points of a fault feature.	Similar to Polylines, points are digitised by individual clicks on the model, or click + drag to continually digitise*. Double click ends digitisation. Single click digitising is default behaviour.

Polylines

There are several options to modify and edit a digitised Polyline and even combine multiple Polylines. Click to expand the Digitise Polyline menu to reveal the sub-menu. In this menu, you can perform several functions:

Type	Defintion	Usage
Draw	Freely draw the Polyline	Click + drag to freely draw the position and length of the Polyline on the outcrop model.
Split Line	Split Polyline into multiple Polylines.	This function is performed at vertices. Click the Polyline to activate and make vertices visible. Click the desired vertex where you'd like to split the Polyline. The Polyline will be split in two and the new Polylines will appear in the interpretation tab.
Join Lines	Join multple Polyelines together. Creates one Polyline.	Hold ctrl and click the Polylines to join together. When all Polylines are selected, choose the Join Lines menu option to combine all selected Polylines.
Add Node	Add a node to a selected Polyline	Select a Polyeline to activate it. Simply click anywhere along the Polyline length to add a node at that location. Add as many nodes as you'd like. Select the Add Node menu option to finish and save newly added nodes.
Create Geobody	Creates a new Geopolygon from multple Polylines.	Select multiple polylines so they are active. Choose Create Geobody menu option to create the new Geopolygon. This is stored in the Geopolygon Interpretations group.

 

Polyline sub-menu

There are other Polyline editing options. These may be accessed by right + click on the Polyline in the Interpretations Panel and navigate to Operations. Another sub-menu opens with multiple options. The most common operations are:

• Refine Spacing
• Remove Dip
• Translate

No.	Type	Defintion	Usage
1.	Refine Spacing	Reduce the number of nodes for the given Polyline by user-defined distance.	If chosen, a dialogue box appears. Simply enter the desired distance, in metres, between nodes along the polyline length.
2.	Remove Dip	Remove the automatically calculated Dip value from the Polyline.	If chosen, a dialogue box is displayed that allows you to enter desired Dip value to remove from the Polyline.
3.	Translate	Translate polyline in any x, y, z direction.	If chosen, a diaglogue box is displayed with separate x, y, z text fields. Enter the desired amount to translate the Poyline.

Other Polyline and Fault editing tools

You can Edit Polylines and Faults during and after creation.

There are several options to edit a Polyeline or Fault.

• Move Vertices
• Pause Digitising
• Undo
• 3D Translate
• Snap Vertices
• Erase Vertices

No.	Type	Defintion	Usage
1.	Move Vertices	Freely move a chosen vertex to any position	Click the desired Poyline or Fault. The nodes will appear. Choose Move Vertices from the Edit bar and click + drag the vertext to the next desired position. Click Move Vertices again to save new vertex position. N.B. you can select a vertex before selecting Move Vertices this vertex will be the updated one when you click the new position. To de-select a vertex simply click on it again while not in an editing mode.
2.	Pause Digitising	Pause activeg Polyline or Fault digitising session.	Whilst digisiting a Polyline or Fault, click Pause Digitising to momentarily pause digitising. This allows you to navigate around the 3D model around. Click Pause Digitising again to resume the digitising session.
3.	Undo	Undoes last action	When drawing a Polyline or Fault, click this to Undo the digitisation.
4.	3D Translate	Move a Polyline or Fault vertex along x,y,z axes	Click on Polyline or Fault to make active. Choose 3D Translate and click on the node that you wish to move. Choose the axis arrows You can either move the node along the x, y, or z axis. Click + drag the plane along those axes allows free movement along that plane's orientation.
5.	Snap Vertices	Snaps digitised vertex to existing vertex nearby
6.	Erase Vertices	Erases selected vertices of Polyline or Fault	Click to activate a Polyline or Fault and display its vertices. Simply click the vertex you want to erase to erase it.

Lineation and Plunges

The Plunge, or lineation, tool is very simple. Select a start and end point for a lineation on the model and VRGS calculates the Dip and Dip direction of the line. Addtiionally, VRGS automatically calculates the Plunge of a Fault that is digitsed on a 3D model.

 

2. Sedimentology Panel

VRGS has several tools key to analysing sedimentary features in 3D outcrop models. The tools included in the Sedimentology section are:

1. Geopolygon (e.g. geobodies)
2. Palaeocurrents
3. Sedimentary logs
4. Boreholes

Type	Defintion	Usage
Geopolygon	Create a Geopolygon outline around interpreted geobodies and extrude it as a solid object away from the outcrop model. Attributes such as Dip and Dip Azimuth and Palaeocurrents may be added to the object to allow further statistics to be measured from it.	Select the Geopolygon tool and click or click + drag the mouse to digitise points along the outcrop. Double click will end digitisation.

A facies name may be added to the Geopolygon. To do this select the active facies from the drop down list at the top of the interpretations tab. Additional facies can be added through the Facies group in the Collections Tree. Once a Geopolygon has been digitsed then extended features can be made available by right + tlick on the Geopolygon in the Interpretations Tree and selecting Make Active. This will provide editing focus to the selected Geopolygon. A new Ribbon Bar will appear in the top menu.

Editing Geopolygons

There are 3 main editing functions for Geopolygons

• Move
• Select Nodes
• Move Nodes

Type	Defintion	Usage
Move	Return to normal model interaction, or Move mode	This quits any active editing to the Geopolygon
Select Nodes	Show all the digitised vertices of the geobody as spheres.	Click on one or more spheres to select them. You can then delete them by pressing the Delete key.
Move Nodes	Move selected nodes	Select a node then click the point on the model you wish to move it to.
Interpolate Nodes	Add node by interpolation between selected nodes	Select adjacent nodes on the Geopolygon and a new node will be interpolated between them.
Add Palaeocurrent	Add multiple palaeocurrent measuremnets to a Geopolygon.	Select Add Palaeocurrent and a dialogue box will appear. You can add a recorded palaeocurrent value in the Azimuth text field. Indicate if it's a bi-directional measurement, such as a trend rather than a known direction. You can and even provide a type (e.g. trough cross-bedding, current ripple cross lamination, etc). Palaeocurrent types are added in the Collections Tree in the Sed Structures menu. To delete a measurement, select the value in the list then press Delete. Right + click on the Geopolygon and select Make Active again to switch off active editing.

Notes about sedimentary Geopolygons

Geopolygons can encapsulate a large rock volume, and it is often the case in sedimentary systems that there is variability in the palaeocurrent directions. We can record this variability by adding those palaeocurrents in the Geopolygon. Outcrops are inherently bias with sedimentary system architecture - the geometry observed on the outcrop exposure is a function of the exposure level and related weathering. However, adding palaeocurrent values to interpreted Geopolygons we can correct for this bias¹,². These can then be used to calculate corrected sedimentary body widths. See the image below for a graphical representation of how to Geopolygons using palaeocurrent data from outcrop³.

Footnotes

1. Fabuel-Perez, I., Hodgetts, D. and Redfern, J., 2010. Integration of digital outcrop models (DOMs) and high resolution sedimentology–workflow and implications for geological modelling: Oukaimeden Sandstone Formation, High Atlas (Morocco). Petroleum Geoscience, 16(2), p.133-154. https://www.lyellcollection.org/doi/abs/10.1144/1354-079309-820 ↩

2. Rarity, F., Van Lanen, X.M.T., Hodgetts, D., Gawthorpe, R.L., Wilson, P., Fabuel-Perez, I. and Redfern, J., 2014. LiDAR-based digital outcrops for sedimentological analysis: workflows and techniques. Geological Society, London, Special Publications, 387(1), p.153-183. https://www.lyellcollection.org/doi/full/10.1144/SP387.5 ↩

3. Burnham, B.S. and Hodgetts, D., 2019. Quantifying spatial and architectural relationships from fluvial outcrops. Geosphere, 15(1), p.236-253. https://pubs.geoscienceworld.org/gsa/geosphere/article/15/1/236/567741/Quantifying-spatial-and-architectural ↩