Extract height value of specific point (x,y) in point cloud

[Roos]

Hello,

I want to extract/discover the height value of specific points (x,y) in a point cloud.

Because I want to compare the (known) height values of a GPS measurement with the height values of the same location in the point cloud.

In the attachment my sample data in LAZ format, and below the coordinates for which I will find the height-values in the point cloud.

Easting                 Northing

121499.630          485947.974

121501.735          485947.616

121503.803          485947.215

121505.510          485947.077

Maybe for (a few) coordinates points do not exactly exist in the point cloud, therefor I want to find the height value which is closest to these coordinates.

Hopefully you can help me, and recommend me which tool(s) I can use.

Thank in advance. I am looking forward to see your response(s).

[Terje Mathisen]

Roos wrote:
> Hello,
>
> I want to extract/discover the height value of specific points (x,y)
> in a point cloud.

The height of what?

Ground, vegetation, a power line or a random bird?

> Because I want to compare the (known) height values of a GPS

> measurement with the height values of the same location in the point
> cloud.
Was this GPS standing on the ground or on a survey receiver with
measured offset between the antenna and the bottom of the antenna stick?

If the answer is that you re only interested in ground points, then you
should first determine if your sample points have allready been
ground-classified or not: If they are OK then the only thing you are
missing is to turn those ground points into either a regular grid or a
TIN before you can use plain interpolation between known grounds and the
GPS locations in order to estimate what the ground value should be in
the same spot.

Terje

>
> In the attachment my sample data in LAZ format, and below the

> coordinates for which I will find the height-values in the point cloud.
>

> Easting                Northing
>
> 121499.630Â Â Â Â Â Â Â Â Â 485947.974
>
> 121501.735Â Â Â Â Â Â Â Â Â 485947.616
>
> 121503.803Â Â Â Â Â Â Â Â Â 485947.215
>
> 121505.510Â Â Â Â Â Â Â Â Â 485947.077

>
> Maybe for (a few) coordinates points do not exactly exist in the point
> cloud, therefor I want to find the height value which is closest to
> these coordinates.

> Hopefully you can help me, and recommend me which *tool*(s) I can use.

>
> Thank in advance. I am looking forward to see your response(s).

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--
- <Terje.M...@tmsw.no>
"almost all programming can be viewed as an exercise in caching"

[Steven F]

You can use lascontrol to do this. Look at it's readme file for details. If you want a specific ground elevation from the lidar you'll need to have a ground classified point cloud, which you can do with lasground if your points are not already classified.

[Roos]

Thank you both! I am only interested in the height of the ground points. I have tried lascontrol and it gave me the desired *.csv result! Once again, thanks.