[GIS] Extracting RGB values from aerial photo and assigning to LAS file with FME

fmeimagerylaslidarrgb

I need to extract the RGB Values from imagery and assign to a .las file in order to display 3d landscape with "real" colours. I have an unlicenced LAStools, FME 2017 and ArcGIS 10.3.1 at hand.

I have tried with las2las, but the tools don't take the option --color-source as was documented in liblas.org. With FME I can visualize this effect but not export to .las.

Has anyone done this?

Best Answer

Use the PointCloudOnRasterComponentSetter transformer in FME. Check out this tutorial: https://knowledge.safe.com/articles/1096/color-and-point-clouds.html

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There is no specific GIS software for doing this: most will handle the RGB image and the Lidar data.

Basically, NDVI is (NIR - RED)/(NIR + RED). Most of the time, aerial Lidar gives you the NIR value (to be checked in metadata) and the first band of your RGB image gives you the RED value. Just make sure that your data are calibrated to reflectance (or, if not possible, normalised in the same range of value -> this will give you a good discrimination, but no absolute threshold can then be used).

As a remark, Lidar does not always provide the intensity information. Sometimes only the distance information is available.

Using Laspy to Create LAS Files from Scratch

Rather than setting the entire points array in one go, try setting each dimension in turn:

import laspy

header = laspy.header.Header()
outfile = laspy.file.File("output.las", mode="w", header=header)
outfile.X = [1, 2, 3]
outfile.Y = [0, 0, 0]
outfile.Z = [10, 10, 11]
outfile.close()

Best Answer

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