common LiDAR point density

[Alessandro Montaghi]

Dear Members list,

I am looking for the common LiDAR point densities used in general. Example following the paper of Vauhkonen et al., 2008 (Effects of pulse density on predicting characteristics of individual trees of Scandinavian commercial species using alpha shape metrics based on airborne laser scanning data, Canadian Journal of Remote Sensing)

1- 0.5 point/m^2 = DEM application

 5-6 point/m^2 = forest application

10 point/m^2 =  Netherlands second coverage

11- 12 point/m^2 = tree-level application

20 point/m^2 = Archaeological application

if you know other National survey coverage (ex: Swedish is 0.5-1) or other LiDAR point density please send me an email. 

Thanks in advance

Alessandro

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Alessandro Montaghi

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[Christopher Crosby]

Alessandro,

We calculate an average shot density for every dataset that we host in OpenTopography. If you are interested in exploring data with a range of densities this might be a place to start: http://opentopography.org/data  For every hosted dataset (red dots on the map), "Shot Density" is displayed above the map near the top of the dataset page - e.g., http://opentopography.org/id/OTLAS.032011.26910.1

In the US, the USGS supported National Enhanced Elevation Assessment report (http://www.dewberry.com/Consultants/GeospatialMapping/FinalReport-NationalEnhancedElevationAssessment) has quite a bit of discussion on costs and benefits for various "Elevations Quality Levels" (defined in part as a function of lidar shot density).

-cc

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Christopher Crosby

Geodetic Imaging & OpenTopography Project Manager

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http://www.unavco.org

http://opentopography.org

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[Alessandro Montaghi]

Thanks Christopher

really great website!!!!!

could I ask you about the term "Shot Density" (eg 4.21 pts/m² ). Is it the density average?

thanks in advance

Ale

 

[Christopher Crosby]

Yes, we calculate the "Shot Density" (a.k.a. "Point Density") as an average for the whole dataset. Obviously the point density on a per m^2 basis can vary greatly across a single dataset as a function of land cover, collection geometry, etc.

-cc

[Martin Isenburg]

Chris,

I am surprised to hear you define it like that. To me "shot density"
suggests that the number of laser pulses per square meter are counted
rather than the number of object + ground hits per square meter. I
like to compute the pulse density and count the number of last returns
(or first returns) per area (here 25 square meters) because that
remains largely unaffected by the ground cover, in particular
vegetation.

lasgrid -i lidar.laz -last_only ^
-density_16bit -step 5 ^
-o lidar_5_5_density.bil

or

lasinfo -i lidar.laz -compute_density

Or did I misread your words and shot density is the same as pulse
density?

Martin @lastools

--
http://rapidlasso.com - fast tools to check LiDAR densities

On Feb 16, 2:42 am, Christopher Crosby <cro...@unavco.org> wrote:
> Yes, we calculate the "Shot Density" (a.k.a. "Point Density") as an average for the whole dataset. Obviously the point density on a per m^2 basis can vary greatly across a single dataset as a function of land cover, collection geometry, etc.
>
> -cc
>
> On Feb 14, 2013, at 7:14 PM, Alessandro Montaghi wrote:
>
>
>
> > Thanks Christopher
>
> > really great website!!!!!
>
> > could I ask you about the term "Shot Density" (eg 4.21 pts/m2 ). Is it the density average?
>
> > thanks in advance
> > Ale
>
> > On Fri, Feb 15, 2013 at 2:24 AM, Christopher Crosby <cro...@unavco.org> wrote:
> > Alessandro,

> > We calculate an average shot density for every dataset that we host in OpenTopography. If you are interested in exploring data with a range of densities this might be a place to start:http://opentopography.org/data For every hosted dataset (red dots on the map), "Shot Density" is displayed above the map near the top of the dataset page - e.g.,http://opentopography.org/id/OTLAS.032011.26910.1
>
> > In the US, the USGS supported National Enhanced Elevation Assessment report (http://www.dewberry.com/Consultants/GeospatialMapping/FinalReport-Nat...) has quite a bit of discussion on costs and benefits for various "Elevations Quality Levels" (defined in part as a function of lidar shot density).

[Jason Stoker]

The project usually does declare an average density.  But shot density != point density from what I have seen. Shot (pulse) density is mainly dependent on laser pulse and detection speed (kHz), aircraft speed and height, and scan angle. Point density is dependent on those as well, but also the number of returns recorded per pulse and the height/density of vegetation. It is usually described by the number of returns you get per unit area, not the number of pulses. This is just what I have seen, it may not always be true.

In the USGS LiDAR spec, Nominal Point Spacing is defined below.  Keep in mind NPS != density necessarily either, as it is calculated on a single swath without overlap, and only looks at first returns. It is really more a way for us to check that we are getting what we paid for.

Assessment of the NPS will be made against single swath, first-return only data, located within the geometrically usable center portion (typically 90 percent) of each swath, acceptable data voids excluded. NPS will be calculated as the square root of the average area per point. Average along-track and cross-track point spacing should be comparable (within 10 percent).

In general, the target NPS for a project should not be achieved through swath overlap or multiple passes. Such collection techniques may be permitted with prior approval.

So IMHO point density can be variable per the unit area it is measured by, and is influenced by the instrument, collection methods (amount of overlap/etc), and cover type. Shot / pulse density is usually a configuration that is programmed in the flight data collection process. So the density you compute using lastools may not exactly match with what the metadata reports. 

And regarding average density over a project- that can open up another can of worms.  If your project has a lot of water in it, you most likely will not get ANY returns back, which will lower your average density over the entire area which isn't exactly fair.

 Clear as mud?

Jason

[Christopher Crosby]

I was not being very semantically precise, OT calculates an average point density for each dataset. Jason's muddy clarification below is of course accurate.

-cc

[Newcomb, Doug]

Oops, that was 1 point per 1-5 meters, averaging 1 point every 3 meters.  That's what I get for trying to give up caffeine.

Doug 

On Sun, Feb 17, 2013 at 6:26 PM, Newcomb, Doug <doug_n...@fws.gov> wrote:

The North Carolina, USA statewide floodplain mapping effort (2001-2006) used posting distances that varied from 1-5 points /meter , average about 3 points / meter.

Doug   

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---------------------------------------------------------------------------------------------------------

The opinions I express are my own and are not representative of the official policy of the U.S.Fish and Wildlife Service or Dept. of the Interior.   Life is too short for undocumented, proprietary data formats.

--

Doug Newcomb

USFWS

Raleigh, NC

919-856-4520 ext. 14 doug_n...@fws.gov

---------------------------------------------------------------------------------------------------------

The opinions I express are my own and are not representative of the official policy of the U.S.Fish and Wildlife Service or Dept. of the Interior.   Life is too short for undocumented, proprietary data formats.