Before a raw LAS/LAZ,E57,PTS or other types of point cloud file can be displayed, they must first be converted to n4ce's own format. Once data has been converted, then the next time it is needed, the Load option is used, rather than the Convert. Converted data should load in a matter of seconds thanks to clever levels of detail. But the conversion process can take a short while depending on the size and geometric proportions of the data. Long thin mobile mapping data can take the longest because the overall extents of the data are so large when compared to the actual volume taken up by the scan data itself. Because the data is not spread evenly, more processing is needed to achieve an even spread of data in the spatial database.
Clicking Convert brings up the following dialog box. No matter how many files are selected to convert, the results is one point cloud.
The import dialog has the following functions:
- Add: Allows one or more files to be added to the list of files to be converted.
- Remove: Removes the currently selected file from the list of files to be converted.
- Merge All Files: When enabled this combines files so that their Scans/Classifications or existing groups are merged. Generally, this option should be...
- Turned Off for E57 files so that any individual scans are kept separate when selecting multiple files.
- Turned On for LAS/LAZ files so that any classifications in the files are combined. Otherwise, it's possible to have multiple occurrences of individual classifications.
- Browse Output File: Specifies the location where the octree files should be generated. By default, this locations is off of the same folder the raw data resides.
- Colour: identifies how colours are encoded. Auto is recommended for this.
- Load Extents: Reads all of the points within the selected files to recalculate the extents. Sometimes this is necessary if the extents stored in the headers of the source files are suspect. Incorrect extents will result in missing data and much longer load times. E57 files are rescanned by default as experience has shown some 3rd party registration tools do not output the correct extents.
- Extents: Displays the overall spatial extents of the selected files.
- Z Is Depth: With some points clouds, the Z value is actually a depth which needs to be subtracted from a given base water level.
- Base Level: Specifies the datum to be used when the Z Is Depth option is enabled.
- Remove Duplicates: Carries out a basic duplicate point check. This will only remove consecutive duplicates.
- Use Groups: Converts Classifications and or Scan locations to groups.
The Grids section contains functionality to allow a grid of levels to be draped over the point cloud. Generally this grid is saved as a real-time grid that is generated on the fly. By storing an origin, grid spacing and the heights, n4ce is able to manipulate vast terrain tiles with minimal effort.
The general workflow is as follows...
- Set the Height Sampling method. The three options are Highest, Lowest or Average. Generally, this would be set to lowest to try and see through noise and vegetation to extract ground levels.
- Set the Grid Spacing.
- Set the Sampling Radius about which n4ce should search for the appropriate point.
- Press Preview Grid.
- n4ce will show a progress bar in the bottom right when finished a preview of the grid will be added to the view.
- Turn the point cloud off or tick "Show Through Cloud" to check the surface.
- If it is not acceptable press Clear Grid (which was Preview Grid) and repeat the previous steps. Turn the cloud back on if it was previously off before trying again.
- If the surface is ok, press "Create Grid". The gridded data import dialog will then be displayed. It is suggested the resulting surface is renamed from n4ce suggestion. Also, small holes can be filled in with the "Fill Across Gaps" option. But this is only recommended for very small holes. The resulting surface will then be added to the project manager as a Lidar grid would have been from an ASC file.
Other options for generating gridded surfaces are as follows...
- 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: Automatically adds the gridded surface to the backcloth of the current model. Usually, this is done to aid digitising in 2d Model window.
- 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 to commit the simplified model to the project. The image below on the left show a 50% reduction, whilst the one on the right is reduced down to only 8%. So large degrees of simplification can still result in data that is relatively true to the original, but only using a fraction of the number of original faces.
- Export Points: Starts the export process
- Use Section: Exports the points visible in the current section, rather than the whole dataset.
- Auto Name: Increments the file name numerically when outputting lots of files.
- Point Count: When outputting to CSV files, this puts the total number of points on the first line.
- Local Coordinates: Saves the points to a local grid near 0,0,0 rather than real world values.
- Select File: Allows the current file name to be specified, and the format of the data to be exported.
- File Name: Displays the current file being or about to be exported.