This article will go through the steps involved when generating Grids from within the 3D viewer. In addition to this, it will also explain how to edit the Grid DTM using a number of different options.
First, open a Point Cloud within the 3D viewer and select the Point Cloud I/O tab. There are some important options you will need to set before we can create a successful Grid.
- Height Sampling: There are three options Highest, Average, and Lowest. Lowest is usually the best as it will pick up points below any vegetation/ noise.
- Grid Spacing: This controls the size of the grid.
- Sampling Radius: The area in which n4ce will look for the appropriate Points. This value can not be more than half the grid spacing.
- Align to Spacing. Ensures the resulting grid starts from a multiple of the spacing, and not the minimum extents, which can be anything but.
Once you have set these values we can now select Preview Grid. A progress bar will appear in the bottom right corner as n4ce generates the grid over the point cloud.
Note: To view the Grid through the Point Cloud we can use the "Show Through Cloud" Function.
Once you are satisfied with the Grid preview please select Create Grid, a new window should appear. From here we can change the Name and many other values about how we would like to create the Grid.
- Disect DTM: This splits the Grid into sub-grids for more effective data access. This should only be used on large data sets.
- Fill across gaps: Generally should be off as this can result in inaccurate edges.
- Optimize Diagonals: This aligns the diagonals on the Grid to follow the strongest trend which results in neater contour lines.
Once you have generated the Grid DTM there will be a new Grid object under the Models node in the spreadsheet view. From here we can double click it to open the Grid view. If you would like to visualise it in 3d after opening the 2d view, please select the 3d viewer icon.
Note: Because of the shear number of contour lines that are possible with large scale grid DTMs they should ideally be drawn as a solid line, so the redraw is as fast as possible. This can be done by selecting Contours > Settings. A new window will appear where we can change the Line Style to Solid.
Other options when generating Grids
- Use Section: Generate the Grid over the data in the section view, rather than the 3d view. This allows n4ce to surface vertical surfaces such as walls and building facades.
- Create As Points: Sends the points in the previewed grid to the current model, rather than generating a Lidar grid. This should only be done with small datasets. Otherwise, a normal model can become swamped.
- Add to backcloth: Adds the gridded surface to the backcloth of the current model.
- Flatten Points: When generating a grid over a section, this lays the points down flat so that they can be visualised flat, rather than standing.
- Align to Spacing: Sets the origin of the grid to a multiple of the spacing, and not to the lowest extent of the bounds of the cloud.
- Show through Cloud. Allows the gridded surface to be seen through the cloud, without having to turn the display of the cloud off.
- Convert to DTM: Creates a simplified DTM from the dense gridded surface. The simplification factor is controlled via the slider below, which specifies a target percentage to try and reduce the number of triangles down to. This can be adjusted until the Create Grid button is pressed.
How to Modify a Grid, in the Grid View
To edit the Grid first open the Grid within the Model view. This is where all of the Grid editing tools are located.
Points > Query: Allows you to see the Coordinates of any point on the Grid.
Points > Height: Gives you the option to change the height of any point on the Grid.
Points > Raise: This option allows you to raise or lower (using a - ) any point on the Grid.
Points > Smooth: This tool allows you to select gaps in the Grid and it will create a best-fit plane to fill it in. Note: Only use this for small gaps/spikes.
Here is an example of the smooth tool being used on a spike: Simply select the immediate area around the spike. A best fit plane will then be put though those points to dial out the erroneous levels.
Points > Assert: This tool allows you to fill in Gaps within the Grid but it uses a near-neighbor algorithm meaning its more accurate than the Smooth tool.
Here is an example of the Assert tool being used: Using either Rectangle or Polygon selection modes, select the zones that need filling in. Multiple areas can be selected at the same time.
Points > Delete: This tool allows you to delete specific areas of the Grid.
Points > Transform: This function allows you to shift the entire Grid or adjust the scale by using Origin Points.
DTM Crop: These functions allow you to remove areas of the current Grid DTM.