Reflectivity - Intensity conversion

[Ron Gilad]

Hi,

 

I am decoding the Velodyne puck 16 packets and writing the points in a LAS format.

I am having issues with converting the point record reflectivity value into the LAS Intensity value.  

 

Does anyone familiar with the needed conversion into the Intensity value by the LAS format?

 

VLP spec

The VLP-16 measures the reflectivity of an object with 256-bit resolution independent of laser power and distance over
a range from 1m to 100m. Commercially available reflectivity standards and retro-reflectors are used for the absolute
calibration of the reflectivity, which is stored in a calibration table within the FPGA of the VLP-16.

The Calibrated Reflectivity value is defined on a scale from 0-255.

 

LAS spec

 

Intensity: The intensity value is the integer representation of the pulse return magnitude. (unsigned short 2 bytes)

 

Thanks,

 

Ron Gilad

GIS Engineer

M: +972-54-789-4543 

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[Evon Silvia]

If you want to do it simply, as the LAS spec states you can multiply the raw values (reflectance) by 256 (65536/256=256) to scale it from 0-255 to 0-65535. Of course, this'll technically give you values from 0-65280 (since 255*256=65280), as Kristian points out here: https://github.com/ASPRSorg/LAS/issues/43

If you'd like to ensure that 255 (8bit max) becomes 65535 (16bit max), you will want to multiple by 257 (65535/255=257) instead.

You can do this in LAStools using las2las:

las2las -i my.las -o transformed.las -scale_intensity 257

Evon

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