Import ​.las/​.laz data

LAS is a commonly used data format to deliver Lidar data captured using techniques such as airborne or mobile data capture systems. As these data capture mechanisms are used during the capture of large geographic areas, it is normal to capture the data in a geo-referenced form. This geo-referenced information can either be embedded within the LAS file as metadata or added during the import process within the Point Cloud Manager Gateway Mode interface. Point Cloud Manager Gateway Mode accepts both geo-referenced and non-georeferenced LAS data.

For geo-referenced data in a specified map projection, to avoid any issues with multiple LAS scans in different projects when the LAS data is loaded into Point Cloud Manager Gateway Mode, the data will be re-projected into an Earth Centered Earth Fixed (ECEF) Cartesian co-ordinate system.

Earth Centered Earth Fixed (ECEF)

Rather than using a projection system where points in the scan data are projected onto a flat surface for the production of maps, using ECEF co-ordinates allows the data to be mapped on to a spherical body which is representative of the Earth’s surface. This allows Point Cloud Manager users to seamlessly use multiple LAS scans within a single project or dataset.

Import process

The import process is as described below:

1. In the Registration panel, right-click the project and select Import to this project. This opens a browser.

2. Select the LAS files to be added and then select Open.

3. Alternatively, select the LAS files to be added in a Windows Explorer window and drag and drop them onto the project node.

Having selected the data to be imported, the Conversion Options dialog is displayed. This enables the user to interrogate the metadata for each file and set the appropriate source projection system if needed.

All the scans listed have one of the following icons that signify the registration type:

• Blue - Georegistered

• Green - Plant space

• Red - Unregistered

The following image displays the different types of icons for each registration type:

Note: Before loading the scan data, it must be either geo-registered or in plant space, and must be of the same registration type.

Metadata

Selecting one of the LAS files within the interface displays the metadata stored within that file in the lower part of the dialog, if it is available. This metadata is optional and will be completed by the service provider that generated the data. When multiple files are selected, the metadata interface displays the list of all the files selected and the number of files selected. Displaying the number of files selected helps ensure the number of files in the interface is as expected, as when selecting thousands of source files it can be difficult to verify if all the files are selected.

The registration type within this section of the dialog provides the projection information within the metadata if specified. If you do not set the projection information, the field will be missing from the interface and it will be necessary to set this directly for the data using the Modify Georegistration button. The provider of the data will be able to supply details of the geo-registration codes to use.

The geo-registration code (to specify the projection of geographic coordinate system) is based on the IOGP EPSG Geodetic Parameter Dataset. This is a collection of definitions of coordinate reference systems and coordinate transformations which may be global, regional, national or local in application (see http://www.epsg.org/). The list of EPSG codes is extensive, there are additional codes such as the ESRI spatial reference codes. Whilst these codes cannot be directly entered through the .las import interface, it is possible to enter the Proj.4 definitions for a spatial reference code. In this case select the Proj.4 toggle within the interface (highlighted below) and enter the code. A good source of spatial reference codes is http://spatialreference.org/.

You can define the Plant system in the Modify Georegistration dialog by specifying the horizontal and vertical units of measure.

Note: If the vertical unit of measure is not specified, it defaults to the horizontal unit of measure.

Number of points in the file

The metadata interface displays the number of points reported in the header block of the source data. It cross-references this with an estimated calculation of the number of points in the file and any difference is reported.

It should be noted that with compressed LAZ files the estimating of the number of points can be imprecise and therefore may be different. The number of points in the file is needed to allow random access to the data for deriving data such as the classification of return points.

Classification of data

LAS data points not only have a position, intensity and RGB value, they also have a classification value. When a single LAS file is selected in the interface and the metadata for the file is displayed, at the end of the metadata interface is a summary of the classification of the points. This table is derived by taking a random sample of points from within the file and reading classification values. There is a small overhead in obtaining this information so the interface may take a second or two to update.

Error messages

In the event where there is an issue reading the LAS data, this will be reported in the metadata interface.