MS60 intensity values

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Chiara_polimi
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MS60 intensity values

Post by Chiara_polimi » Thu May 17, 2018 3:56 pm

I have used a multistation Leica Nova MS60 to make surveys for my thesis work. Unfortunately, I'm not expert at all and I have some doubts (probably simple and elementary). One concerns the intensity values: the point cloud extracted from the instrument is characterized by a scalar field that, if I'm not mistaken, are the intensity values of the returned signals and depend on the distance/angle of incidence/reflectivity of the surfaces... how do I interpret these values? how is the range determined? unit of measure?
I'm looking for an explanation, even elementary, of how to use this data :)
Thank you all,
Chiara

I enclose a histogram of one of the point clouds processed with cloudcompare as an example
Histogram.png
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James Hall
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Re: MS60 intensity values

Post by James Hall » Thu May 17, 2018 5:58 pm

I can't answer most your questions as I do not understand the criteria and units Leica uses. From what I have observed each scan setups intensity values are relative to that scan. (distance, angle) Comparing Intensity values for separate scans of the same object will give you different values. The difference in intensity value between dissimilar materials are probably comparable.

You would have to calibrate your intestacy values from separate scans on a single object to compare the Intensity differences from other scans.

There are a few field conditions that affect reflectivity. If all objects in a scan were the same materiel. You would have intensity values based solely on distance and angle and would notice a red shift with distance. Similar to a Doppler red shift in astronomy. Another red shift would occur at grater angles were most of the lasers emergency is being bounced away from the Scanner.

Salts, calcium deposits, soot and other surface contaminates affect reflectivity.

Translucency also plays a roll.

Color Albedo is probably the most significant factor in the intensity reading.

If you look a .pts file saved out of Cyclone. The first 3 sets of numbers are Nothing Easting elevation. 251.693203 127.459277 -1.863424
The Intensity values are the last 4 sets of numbers. -1662 3 0 0

251.693203 127.459277 -1.863424 -1662 3 0 0
251.690271 127.448347 -1.855398 -1719 2 0 3
251.688075 127.448923 -1.865008 -1487 32 1 9
251.677631 127.479890 -1.857028 -1738 15 1 1
251.728703 127.477897 -1.858670 -1748 1 1 1
251.729666 127.485849 -1.858681 -1688 7 2 22
251.705959 127.449992 -1.858617 -1796 1 1 1
251.706121 127.459330 -1.860230 -1734 0 1 0
251.785019 127.508516 -1.857153 -1657 1 1 1

They are using at lest 24 bit color depth if not more.


If you checked the property on a single point in cyclone you would see something like the below example.
The Intensity values seam to be assigned up to 10,000 different values. You would need to talk to Leica for hard information.

Minimum Intensity = 0.0127
Maximum Intensity = 1.0000


Name: <9BE0>
Object Info:
Original ScanWorld = BLK360_3500799_Setup8
ScanWorld Name = ScanWorld [Registration 1]
Scan Name = Scan-1
Begin Time = 05/05/2018 19:05:30
Number of Points (Estimated) = 12101258
Minimum Intensity = 0.0127
Maximum Intensity = 1.0000
Bad Face Min Depth Change = 0.32808 ft
Bad Face Max Incidence Angle = 87.000 deg
Bad Face Normal Angle Consistency = 5.000 deg
Color = [0, 255, 0]

Contains data types:
(Points)(Intensity)(Color)(Normal)(Grid)

Point Cloud Specifics:
Complexity = 9
Scan azimuth resolution = 0.036 deg
Scan elevation resolution = 0.055 deg
Scanner's position = (245.38186, 132.05625, 1.19834) ft
Scanner's direction = (-0.4995, 0.8663, -0.0007)
Source ScanWorld = ScanWorld [Registration 1]

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Re: MS60 intensity values

Post by Macgyver » Fri May 18, 2018 4:11 am

Intensity is the amount of laser light returned to the scanner. It is unit-less/dimensionless. IE The values are not in watts/joules.
The scale and range is arbitrarily setup by each manufacturer and the values are often used in the scanner's calibration algorithm / lookup tables.

Many things affect intensity but the main ones are range (distance from the scanner), reflectivity and angle of incidence. A flat white wall close to the scanner will be higher intensity that one far from the scanner. A perpendicular wall will be higher intensity than a wall angled to the scanner (at the same distance from the scanner). A white wall will be higher intensity than a black one (at the same distance from the scanner). Since there are so many factors at play you can get things like an angled black wall being higher intensity than a perpendicular flat wall simply because it is much closer to the scanner. You can also get other factors at play like the wet area of a wall being lower intensity than the rest because water absorbs infrared.

In a practical sense you cannot use the intensity value to determine materials. EG You cant say that an intensity of 2000 is red brick and an intensity of 1000 is bitumen. What you can do though is compare intensities at similar distance and angle of incidence. A real world example would be scanning a road and colouring the scan by intensity; then you would able to digitize the road markings as the while lines will show up higher intensity (brighter) than the bitumen. Intensity is especially useful when you are not collecting photographic information with the scan.

Intensity can also indicate the quality of the data. Often low intensity data has a higher standard deviation on the range measurement. IE Low intensity data is "noisier" and you will notice this when dark objects look "Fuzzy". This varies a lot been makes and models of scanners though.

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Re: MS60 intensity values

Post by Chiara_polimi » Fri May 18, 2018 2:06 pm

Thanks for your help and for your answers! I think I will avoid dealing with these values in my work, I will probably limit myself only to a qualitative assessment on the distances / angles / materials.

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Re: MS60 intensity values

Post by smacl » Fri May 18, 2018 3:28 pm

Chiara_polimi wrote:
Fri May 18, 2018 2:06 pm
Thanks for your help and for your answers! I think I will avoid dealing with these values in my work, I will probably limit myself only to a qualitative assessment on the distances / angles / materials.
From a practical point of view, intensity can be very valuable to the end user for picking out features such as road markings and signage that are not geometrically distinct from the surrounding data. There's no time overhead that you get with colorization of scans, nor other data misalignment errors you can get with colouring. We currently normalise it after removing outliers in our own software, though reading the above, distance weighted normals might make for better results where the scanner position was available.

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