Strata¶
Use this dialog to define strata properties for an application layer (type GMI). You can use the application layer to define a subsurface layer, such as terrain surface (soil) or ground conditions (rock).
Where do I find the dialog?¶
Select the application layer (GMI) in the vertical list, right-click (or double-click), and choose Properties.... Then go to the Strata tab.
Strata Type¶
Gemini Terrain supports many strata types. Some are predefined, while others are user-defined, as shown in the table below.
| Strata No. | Category |
|---|---|
| 00 | None |
| 01-05 | Soil |
| 06-10 | Rock |
| 10-15 | Mass Replacement |
| 16-20 | Topsoil |
| 21-25 | Vegetation |
| 91-95 | Tunnel |
| 101-500 | User-defined |
Use the None strata type for application layers that contain plan and map themes that should not be included in a subsurface layer, such as layers for municipal and zoning plans, buildings, properties, and land use.
The order of the strata in the application layer list must correspond to the order of the strata in reality.
In reality:
The different strata as they appear in reality: A = Vegetation, B = Topsoil, C = Mass Replacement, D = Soil, E = Rock
Order of strata in the application layer list in Gemini Terrain
Used strata are marked with a + at the end. Note that only application layers added to open drawings are checked in this context.
With the Used strata... button, you get a complete overview of all strata added to one or more drawings in the project. Application layers not in use in the project are not listed.
If you change the strata type for an application layer, only that layer is reset and/or recalculated, not all others. This ensures optimal performance in large projects with many strata.
Theoretical Layer¶
For user-defined layers, you can select that the layer should be theoretical.
No construction will be performed against these layers, and the layers will be theoretical when generating profiles.
Construction Priority¶
With this option, you can prioritize one strata over another, for example, surveyed data over digital map data, when building XFI and EFI models.
The default is construction priority "default".
Any priority set on the application layers is also considered when creating phantom layers for use in mass calculation.
Example where the phantom layer TOP SOIL (dashed red line) is created from Layer 1: Soil (green) and Layer 2: Soil (blue) with default priority on both layers
Example where the phantom layer TOP SOIL (dashed red line) is created from 1: Soil (green) and 2: Soil (blue), with priority 1 on layer 2: Soil
The priority set on the application layer is also transferred to SFI models when you generate profiles.
Method for Calculating Terrain Grid¶
Based on the original data (contour lines, triangulated networks, and point clouds) in the application layer, the program calculates a strata as a grid, i.e., a rectangular mesh with elevations. If two or more layers are defined with the same strata type, for example, 01: Soil, the program uses the data in all layers to calculate the grid.
The calculated grid is used both in calculations and for 3D visualization. You can choose the desired density. There is one density for calculations (Gemini Terrain - Project Settings) and one for 3D visualization (Drawing Settings).
The following calculation methods are available:
- None
- Automatic: Uses triangulated network, point cloud, or contour lines
- Contour lines: Uses elevations in lines and polygons
- Triangulated network: Uses elevations in triangulated network
- Point cloud: Uses elevations from points
Use None for tunnel data and layers containing data that do not represent a strata, Contour lines for digital maps (contour lines), and Triangulated network for surveyed triangulated data. Point cloud is used for scanned ground data.
For the Automatic method, the following rule applies: The program first checks if the application layer (GMI) contains a triangulated network object, then a point cloud object, and finally lines and polygons. The automatic method uses the first available data source in this order.
Info
The calculation methods are described in detail in the section Define strata in the user documentation.
Calculation Method for Longitudinal and Cross Sections¶
With the Gemini profile generator, you can create longitudinal and cross sections. All application layers defined as a strata can provide a layer in the profile. You can choose between three methods:
- Automatic
- From original data
- From terrain grid
The From original data option means the program uses elevations from data in the application layer, while From terrain grid means the program uses elevations from the calculated grid.
Info
The differences between these methods are described in more detail in the user documentation.
For the Automatic method, the following rule applies: * If the grid is calculated from contour lines, the program uses From terrain grid. * If the grid is calculated from a triangulated network, the program uses From original data.
Reference Strata¶
Using a reference strata allows you to calculate a strata based on values relative to another strata. The use of reference strata is described below with a practical example.
During design, the subsurface layers are often uncertain. They can be constructed based on fully analyzed point data from ground surveys, but the accuracy of the surfaces depends on the number of boreholes in the area. These data normally refer to the terrain surface layer, which must then be set as the reference strata.
You have information about x, y, and depth for all boreholes. These must be imported into the application layer and triangulated in the same way as surveyed terrain models. You must also set triangulated network as the calculation method.
The depths in the triangulated network are relative to the reference strata. For boreholes, you must choose to subtract elevations from the reference strata.
Handling Elevations in Areas Without Data (Outside Limiting Contour)¶
The default option is Set as undefined. This can affect the terrain grid if there is a limiting contour around the data.
Example
A typical example is when you have created a triangulated network from surveyed data. All grid points outside the limiting contour will then be undefined.
Undefined grid points outside the limiting contour
This means that longitudinal and cross sections stop at the limiting contour when you generate profiles from the terrain grid, and that mass calculation with volume contour is not performed in the undefined areas.
Profiles stop at the limiting contour
The Do nothing (may extrapolate the terrain grid) option works differently depending on the settings.
If you select a reference strata together with Use elevations in the strata as relative elevations to the reference strata, you will not get a terrain grid in areas without data. This is typical for borehole data where the elevations are given relative to the terrain surface.
In other cases, the program will extrapolate the grid all the way to the terrain model area. You cannot influence the grid calculation in these areas (it is as it is).
Example of extrapolated grid
With the Use elevations from reference strata and add value option, the elevations in the reference strata are copied outside the limiting contour. This option is relevant if you want to combine data from two different layers. A typical scenario is that you have a digital map for the area but have surveyed parts of the area where high accuracy is required.
You can also add or subtract a value from the elevations outside the limiting contour. In the example below, no value is added.
Figure: A = Soil layer is the reference layer for the rock layer, B = Limiting contour
This option also gives you another possibility: If the application layer does not contain any data, you can quickly create a strata parallel to the reference strata by entering an offset value. By entering -1, you get a layer 1 meter below the reference strata.
Visualizing Grid, Triangulated Network, and Excavation¶
You can set the color of the grid and whether, and how, it should be displayed in 3D view. The default settings are green color and checked for Show grid in 3D view.
Roads, intersections, and pits will make an excavation in the grid if Perform excavation is checked under Drawing Settings. All elevations in the grid will then be adjusted to match the excavation.
By default, the program does not show the adjusted grid. If you want to see this, you can check Show adjusted grid.
Adjusted grid not shown
Adjusted grid shown
You can also use the Material option to select which texture to use in rendering (surface treatment).
Excavation visualized with material
If background image display (WMS/BGR application layer) and Show strata are active, the terrain grid will be used for draping unless you check Drape raster on triangulated network. For grid, you always get smooth shading, while for triangulated network you can choose between smooth and hard rendering.
Smooth rendering
Hard rendering
Note
You may experience interference if you display both the terrain grid and triangulated network at the same time.