LAS Import Operation

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The Import LiDAR Operation imports LiDAR data from files in LAS or LAZ format into an MRP. Drop down the Point Processing menu button and select Import LiDAR to begin an operation. 

The import operation is repeatable, and editable. After you execute the operation, the parameters will be saved in an XML file which will thereafter be listed on the Import LiDAR menu. Select this item in the menu to reopen the property dialog. 

You can choose to restart the operation. Simply edit the parameters as required and execute the operation again. Alternatively, you can choose to add new data to the existing MRP file. Identify the new source files you want to import and execute the operation to extend the MRP file. 

The operation generates an MRP file with a LAS flavour. The band structure is fixed, and all LiDAR pulse-return data will be automatically imported. All you need to do is to make sure the coordinate system is correct, set the cell size, and specify the input source files. 

MRP Format 

A LAS_MRP contains the following bands. 

X                    REAL 64 bit
Y                    REAL 64 bit
Z                    REAL 32 bit
Classification        Unsigned Integer 8 bit
Intensity            Unsigned Integer 16 bit
Red                  Unsigned Integer 8 bit
Green                Unsigned Integer 8 bit
Blue                 Unsigned Integer 8 bit
NIR                  Unsigned Integer 8 bit
GPS Time             REAL 64 bit
Scan Angle           REAL 32 bit
User Data            Unsigned Integer 8 bit
Point Source ID       Unsigned Integer 16 bit
Number of Returns     Unsigned Integer 8 bit
Return Number         Unsigned Integer 8 bit
Flag Info            Unsigned Integer 8 bit 

The “Flag Info” band contains bit-flags as shown below.

KeyPoint             Bit 0
Synthetic            Bit 1
Overlap              Bit 2
Withheld             Bit 3
ScanDirection         Bit 4
LineEdge             Bit 5
Scanner              Bits 6-7 

All data in an MRP is compressed using a standard lossless algorithm. 

First time use 

Firstly, select the LAS and/or LAZ files you want to import. ProRaster imports files that are compatible with LAS specification 1.4 from the Open Geospatial Consortium. LAZ files are compressed LAS files generated by the laszip library. You can use a file browser to select files individually or in groups. To select all files of a particular type from a folder, select the file type in the drop list, then browse to the folder. If you make a mistake, hit the red button to delete all inputs and start again. 

Specify the output MRP file. Make sure that the output location has sufficient storage space. If you are overwriting an existing MRP file, make sure it is not already open in ProRaster. A list of recently accessed MRP files is provided for convenience. 

Set the Temporal Storage Mode to “Accumulate”. You only need to consider this parameter if you plan to build an MRP by running multiple import operations. See “Extending” below for more details on this setting when adding data to an existing MRP file. 

Now define the properties of the MRP file. You can set a name which will be used when you display or grid the points. You can also include metadata of any kind from a text file. For example, this file might list surveying parameters. It is likely that this file will contain data in XML format, but it does not have to. The text file will simply be written into the MRP for future reference. 

It is critically important to specify the coordinate system of the data. The system expects that all the LAS/LAZ files you import will have data that is in this coordinate system. No reprojection is performed when importing. The projection can be acquired from the LAS/LAZ files and ProRaster will attempt to do this as soon as you specify your import files. However, this information is often missing or sub-standard and it is important to check it and override it if necessary. 

You can specify the units for the Z band (RL). Usually, LiDAR data is stored in metres, and occasionally in feet. This information is typically not recorded in the LAS file, and you are encouraged to supply it. 

Finally, specify the cell size (see detailed notes previously). Typically, a cell size of between 0.2m and 1.0m is appropriate. 

Hit OK to begin the import process. ProRaster will report information as it loads each source file. If the files are located on an SSD they may be imported in parallel, otherwise they are processed one at a time. If everything completes correctly the MRP file will then be displayed in ProRaster. 

Restarting 

If, after completing the operation, you are not happy with the outcome or you realise you have made some mistake, you can repeat the operation. Your operation parameters have been saved into an XML file along with the MRP file (of the same name). 

On the Point Processing > Import LiDAR menu, select the XML file that contains the operation properties you wish to restart. When the dialog opens, hit the “Restart” checkbox near the top right corner. You are now free to edit the operation parameters. Note that if you do not change the output MRP file name, the existing file will be overwritten. Hit OK to restart the import process. 

If your XML file is not visible on the list, you can still edit or restart the Import LiDAR operation. Just drag & drop the XML file onto ProRaster Scientific and the import dialog will open reflecting the properties recorded in the XML file. 

Extending 

You can add more data to an existing MRP by running the operation again. Your operation parameters have been saved into an XML file along with the MRP file (of the same name). On the Point Processing > Import LiDAR menu, select the XML file that contains the operation properties you wish to modify and execute. 

Firstly, do not check the “Restart” button near the top right corner. By leaving this unchecked you are indicating that you wish to add new data to an existing MRP. All you need to do is specify the new LAS/LAZ files you want to import. You cannot change any other parameters. 

The LAS/LAZ files that you have already imported will be listed with a “*” prefix. This is not just for information. It also tells you that ProRaster will never process these files again, even if you browse to them or add them into the import list. Select the new LAS/LAZ files that you wish to import. For example, you can just add all *.LAS files from a folder and, even if some have been previously processed, only the new files will be selected for processing. 

To use this feature, you must set the “Temporal Storage Mode” correctly when you first create the import operation. There are three options – Accumulate, Accrete, and Repeat – and these control whether the new data is added to a new temporal event, and what kind of event it is. 

Accumulate 

Accumulate is the most commonly used option. It adds all the new data into the same temporal event as any existing data. Your MRP will only ever have one temporal event in it. You are building one contiguous point cloud dataset. 

  • There is only one “Total Replacement” event in the MRP.
  • Each time you import more data, it is added to the existing event.
  • Overviews levels get updated efficiently each time you import.
  • Statistics are recomputed completely each time you import.
  • When you grid the MRP all points are always used. 

Accrete 

The Accrete option adds a new temporal event each time you add new data to the MRP. It allows you to differentiate between different phases of a survey by time but still allows you to treat the entire survey as a single contiguous point cloud dataset. 

  • Each event in the MRP is an “Partial Replacement” event.
  • Each time you import more data, it is added to a new event.
  • Overview levels are created for each new event efficiently.
  • Statistics are recomputed completely each time you import.
  • When you grid, use points from an event, a range of events, or all events. 

Repeat 

The Repeat option effectively creates a new dataset, with a new event time, each time you import data. It is designed for scenarios where you are repeatedly surveying the same area and tracking changes to the terrain in that area. An example might be a mining company surveying an ore dump to measure changes in volume over time. 

  • Each event in the MRP is an “Total Replacement” event.
  • Each time you import more data, it is added to a new event.
  • Overview levels are created for each new event efficiently.
  • Statistics are computed for each event separately. There are no global statistics for all events.
  • When you grid, only use points from a single selected event.