What are Extra Bytes?
Officially introduced in the LAS v1.4 specification, Extra Bytes is a mechanism which allows a developer to define extra data fields of various types. They are a means to extend the LAS format to add additional information to each point, literally adding extra bytes of data on a per point basis. Each point stored in a LAS file has a prescribed size per point based on the standard attributes that are included with each point according to its point data record format (PDRF). The additional data is added in a manner that any software can dynamically read the information as there is an Extra Bytes VLR used to describe the data type of the extra information included with each point. Metadata about the additional data in the file may be needed to understand the contents, more on that later. If a software doesn’t do anything with these extra bytes it will carry them on when reading and saving the point data.
Riegl was one of the early adopters and published their Riegl Extra Bytes specification to provide extra context and explanation behind the extra bytes they may add to data from their various sensors. Agisoft joined the field just a couple years ago, with the ability to add their confidence and normal to points generated from photos by Metashape.
GeoCue’s LP360, formerly known as TrueView EVO, started using Extra Bytes for storing computed values from geocoding, such as range and incidence angle, that would be useful again later for additional processing or tools such as Image Explorer. This, in turn, resulted in LP360 getting some oft requested tools for Extra Bytes. Extra Bytes defined by us for TrueView systems are always preceded by “True View”.
The ASPRS LAS working group has been working on the standardization of common Extra Bytes through an ongoing discussion. Their work is an attempt to prevent multiple different names for the same attribute; to protect standardized names from acquiring multiple different meanings; to provide a centralized location to learn more about Extra Bytes that are discovered in one’s dataset; and, to provide a method to publicize and therefore increase the value of Extra Bytes that users have produced.
Display
As extra bytes are additional attributes on point data, then some of them may be suited to visualization of the point cloud. In LP360, v2021.1.47.0, the ability to symbolize and filter Extra Bytes found common across all LAS files on a LAS Layer using Live View was introduced.
Query Extra Bytes
As an attribute on a point, it can be useful to be able to query for an Extra Byte to get the value for a specific point. In LP360, the Identify tool can be used to query the attributes belonging to a specific point or group of points. Identify will display in the Identify Tab any Extra Bytes that exist on the point.
Workflow Automation
Throughout LP360, the source point filters for classification and point cloud tasks (PCTs) allow for filtering using up to three simultaneously active Extra Bytes.
Exciting Development
The recent developments to support Extra Bytes in LP360 have given users the ability to visualize, query, and use Extra Byte information more than ever before. This has opened some exciting possibilities for workflow enhancements. Further development and standardization of additional Extra Bytes for both derived and new attributes will continue to help support workflow automation and efficiencies for classification and extraction of information from point clouds.
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