Ground points density needed to generate a DTM

[Silvia Franceschi]

Dear all,

I am trying to understand if there is some literature about the recommended number of ground points (classified as ground in the LAS file) needed to generate a good DTM at different resolutions. In particular I am interested in 0.5 and 1 m grid resolution.

Considering that the classification of points can be not so precise, do you have any idea on what sort of index on a LiDAR point cloud is it possible to evaluate, to understand the maximum resolution of the derived DTM?

If you have some articles or posts or experience in this, I would really appreciate your help.

Thanks in advance

Silvia

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ing. Silvia Franceschi
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[John Wall]

Silvia,

My experience has been that two lidar points per grid cell is sufficient. If you know the point spacing, you can use that spacing or half it it.

-John

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John Wall, Graduate Teaching Assist.

Earth Science Ph.D. Student

Department of Marine, Earth & Atmospheric Sciences

NC State University; Office: 4139 Jordan Hall

Department Profile: meas.sciences.ncsu.edu/people/jwall/

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[Mihai Tanase]

Check Montealegre et al. 2015 in Remote Sensing.
He has two papers on filtering and Dem.

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[Alessandro Montaghi]

Hi Silvia, 

In the section DTM of this paper, you can find several reference papers about DTM, density, etc.. If you need more specific case send me please a personal email.

http://www.sciencedirect.com/science/article/pii/S0303243412002024

Airborne laser scanning of forest resources: An overview of research in Italy as a commentary case

International Journal of Applied Earth Observation and Geoinformation, Volume 23, August 2013, Pages 288-300

Alessandro Montaghi, Piermaria Corona, Michele Dalponte, Damiano Gianelle, Gherardo Chirici, Håkan Olsson

Best, 

Alessandro

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[Lewis Graham]

A good rule of thumb is to have two ground points per spacing grid.  This is basically the Nyquist Sampling Criteria. 

For example, if you have 2 ground points in a 1m x 1m grid then you can construct a DEM with a 1 meter post spacing but no smaller.  You must use a resampling technique that properly filters the data – something such as an inverse distance weighted (IDW) respampler.  You should not use TIN sampling. 

 

Lewis Graham

GeoCue Group

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[Silvia Franceschi]

Thank so much to you all!

I will take a look at all the documentation you sent to me, and in case I will come back with other questions...

Many thanks again!

Silvia

[Silvia Franceschi]

Hi John,

thanks for the answer, do you know if there is a way to calculate the average point spacing of a LAS using LasTools?

Silvia

[Alex McVittie]

lasinfo with the -cd flags passed in should return the point spacing
along with the rest of the metadata.

lasinfo.exe -cd lidardata.las

[Trymore Chivinge]

Hi Silvia,

If you have not got an answer yet, the best guidance is probably at:

Density and Spacing of LiDAR

Density and Spacing of LiDAR Recently I worked with LiDAR from an Optech Gemini scanner in the Philippines and with LiDAR from a RIEGL Q680i ...

 

Kind regards, 

 Trymore 

[Silvia Franceschi]

Sorry John,

I can not understand... if I need two LiDAR points per grid cell, once I have the point spacing I should double it no half to get the "optimal" resolution for the derived DEM... 

Am I missing something or just thinking wrong?

Silvia

On Fri, Nov 4, 2016 at 4:46 PM, John Wall <jw...@ncsu.edu> wrote:

[Evon Silvia]

Silvia,

I agree that generally 2ppsm will suffice for a 1m DTM in most areas. However, if your area of interest is covered in moderate to heavy vegetation or in steep terrain, we've found that your planned point density will need to be more like 6-8ppsm in order to get the requisite density on the ground. We frequently find 2ppsm to be woefully inadequate to produce a decent DTM in the heavily forested western USA.

Evon

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[Lewis Graham]

Agree.  That is why, in my rule of thumb, I say two ground points per grid cell size.

[Silvia Franceschi]

Thanks Evon,

that is in fact what happens in my case... I have an average point density of 8 pt/sqm but I have very few points at ground because of vegetation, the density of them is less than 1 pt/sqm. My question was in fact about the density of the points at ground not of the whole cloud. What do you think is a good value of the density of  ground points for a DTM at 1m resolution?

Silvia