smoothing

[Alison Cramer]

Hi all,

I have drone imagery of a waste rock pile from an abandoned mine, which I have successfully classified and removed veg from using lastools.  I have also made a great dem.  I am attempting to smooth the rills, little erosional patterns, on the pile only, but I have come up short.  My end goal is to calculate the volume of the erosion using other software, but I need a smooth pile first.  I have tried the smoothing in Arc, but I lose elevation and the entire image becomes flat.  I have tried lasgrid, which I think works, but then I am unsure of how to convert that back to a dem to make sure that I have kept elevation and the integrity of the rest of the image.  Any advice would be most welcome.  

I would also like to fill the holes in my classified image with points.  The dem looks nice except for the holes, where blast2dem just fills them with a shiny gray strip.  I would somehow like to interpolate the points surrounding the holes so that those are filled in with ground points that match the surrounding area's elevation.  If anyone has any ideas on how I could go about this please let me know.  

Thanks for the great tools Martin!!  I love lastools and everything it has to offer.  

Cheers,

Ali Cramer  

[Ted Hutcheson]

Allison,

What you're looking to do requires a mix of back and forth unfortunately (Martin might have a different solution), which you can do in ArcGIS or QGIS by processing a new DEM from your work and interpolating (using whichever method you want) the new elevation data from the DEM you've already created if you want to include those missing spots.  From there, you can then extract the elevation model as points at a high resolution and then convert them back into LAS with the proper classification and merge the LAS files, or you can create another DEM at the same resolution as the existing and merge the GRID or DEM files together and create a combined surface, note that for proper results you'll need to create the DEM's at the same raster resolution to make the data comparable in that way.  I always tend to interpolate a high resolution and then decrease the resolution from the higher interpolated file.

Hope that helps a bit...

Ted.

Ted Hutcheson, B.A., GISP, Adv. RPAS

Geomatics and Aerial Data Specialist

Point of Interest Aerial

244 Colton Circle

Kitchener, ON  N2A 4K2
c: 519-590-9999

e: tedhutc...@gmail.com

w. www.poiaerial.com

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[Martin Isenburg]

Hello Alison,

without giiving us access to your current results and the data (via a link only!!!) for an area that is a representative example for the struggles you are dealing with it will be impossible to come up with some good suggestions.

Regards from Panama,

Martin

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[Alison Cramer]

Hi Martin and Tim,

Thank you for your fast response.  I haven't had any luck using arc, and the interpolation methods.  Here is a link to my classified dem and the original laz file.  I want to fill the holes in the laz file prior to making the dem, but I am not sure how to do that in lastools.  I don't like the way that blast2dem fills the holes with the smooth silver strips.  Is there a way around that?  In addition, I am trying to smooth the pile.  That's the hill in the middle of the image.  Thank you all for your suggestions.  I love these tools, just trying to finish up my masters degree and make everything look really nice.  

Cheers,

Alison Cramer    

https://drive.google.com/drive/folders/1X_jeSskv6XXrsyy73d5uKn0pdqtfUhWv?usp=sharing

To view this discussion on the web visit https://groups.google.com/d/msgid/lastools/CABSWR-GpcOxb-wXcuXH39_OUQKC1q5447uFfL1Z6p0nXQgFakQ%40mail.gmail.com.

[Peter Guth]

Hi Alison,

Instead of 1 cm grid spacing, I would go with 1 decimeter.  The DEM looks much better then (and it will be smaller and easier to work with, and I don't think there is any valid reason to go with the grid spacing you have).

Then you should try to figure out why you have holes (what failed in the data collection), if you can live with them, or how you want to interpolate across them.  The better grid spacing might be enough to make the interpolation you were using work better.

To view this discussion on the web visit https://groups.google.com/d/msgid/lastools/CAH88P_oaBBzipobWhOMgFFN4Wt9%2BBLtQt%2BKhTM4NE3379SoZTw%40mail.gmail.com.

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Peter L. Guth
Professor, Dept Oceanography, USNA

[Alison Cramer]

Hi Peter,

I will look at the decimeter grid, thanks for looking at my work.  I chose 1cm because that’s the resolution in my imagery.  I have holes because of trees.  This is drone imagery, so when I remove vegetation, I get holes.  

Alison Cramer

Sent from my iPhone

On Dec 2, 2019, at 2:55 PM, Peter Guth <pg...@usna.edu> wrote:



[Martin Isenburg]

Hello Allison,

here is one way to smooth your data. Create 4 shifted (!!!) average grids with a 10 cm cell spacing while filling smaller holes and then merge them into one 5 cm grid spacing that you then interpolate with blast2dem to fill the holes.

:: create four shifted 10cm average grids

lasgrid -i allison\A18_merged2.laz -keep_class 2 -step 0.1 -grid_ll 0.00 0.00 -average -fill 5 -odix _10cm_00_00 -olaz

lasgrid -i allison\A18_merged2.laz -keep_class 2 -step 0.1 -grid_ll 0.05 0.00 -average -fill 5 -odix _10cm_05_00 -olaz

lasgrid -i allison\A18_merged2.laz -keep_class 2 -step 0.1 -grid_ll 0.00 0.05 -average -fill 5 -odix _10cm_00_05 -olaz

lasgrid -i allison\A18_merged2.laz -keep_class 2 -step 0.1 -grid_ll 0.05 0.05 -average -fill 5 -odix _10cm_05_05 -olaz

:: merge and hole fill into one 5 cm grid but don't cover areas of over 1 meter without data

blast2dem -i allison\A18_merged2_10cm*.laz -merged -step 0.05 -kill 1.0 -o allison\A18_merged2_05cm.laz 

:: hillshade to quality check

blast2dem -i allison\A18_merged2_05cm.laz -hillshade -step 0.05 -kill 1.0 -o allison\A18_merged2_05cm_hillshaded.png
   

The resulting hillshade (resized to 25% and converted to JPG with IRFANview) is attached.

Regards,

Martin @rapidlasso

[Mark Levitski]

I just don't understand why you'd want to smooth all the little "rivulets" if you're trying to do volumes on th erosion.  If you have a point cloud you just create a tin and compare to the surface before the erosion. Sounds like I am misunderstanding or you are over complicating. Smoothing removes the details of the erosion 

On Tue, Oct 13, 2020, 9:07 PM Quan Tran <qhon...@gmail.com> wrote:

Hi guys, 

This is a very helpful topic. I have been testing this out on my side and it is working very well. I do have a question, can the last command ( blast2dem -i allison\A18_merged2_10cm*.laz -merged -step 0.05 -kill 1.0 -o allison\A18_merged2_05cm.laz ). 

Can we add   "-set_classification 2 " to the above blast2dem cmd? 

eg.  blast2dem -i allison\A18_merged2_10cm*.laz -merged -step 0.05 -kill 1.0 -set_classification 2  -o allison\A18_merged2_05cm.laz  

I am trying this on my side but the A18_merged2_05cm.laz  file shows no classified point clouds. 

Many thanks

Quan

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[Martin Isenburg]

Hello,

this will require two steps. When writing a raster to LAZ (aka "RasterLAZ") the classifications are not written (at the moment).

blast2dem -i allison\A18_merged2_10cm*.laz -merged -step 0.05 -kill 1.0  -o allison\A18_merged2_05cm.laz

las2las -i allison\A18_merged2_05cm.laz -set_classification 2 -o  allison\A18_merged2_05cm.laz

However ... this is EXACTLY why I find LAZ and exciting raster format for elevation rasters.

https://groups.google.com/g/lastools/c/39hR_4BvvIA/m/EPIDR2hhDAAJ

You can easily create a classified DEM that will be just a DEM to those who only care about elevation but can also provide land cover classification to those doing additional analysis. RasterLAZ naturally provides the concept of a classified elevation raster.

Regards,

Martin 

On Wed, Oct 14, 2020 at 4:07 AM Quan Tran <qhon...@gmail.com> wrote:

Hi guys, 

This is a very helpful topic. I have been testing this out on my side and it is working very well. I do have a question, can the last command ( blast2dem -i allison\A18_merged2_10cm*.laz -merged -step 0.05 -kill 1.0 -o allison\A18_merged2_05cm.laz ). 

Can we add   "-set_classification 2 " to the above blast2dem cmd? 

eg.  blast2dem -i allison\A18_merged2_10cm*.laz -merged -step 0.05 -kill 1.0 -set_classification 2  -o allison\A18_merged2_05cm.laz  

I am trying this on my side but the A18_merged2_05cm.laz  file shows no classified point clouds. 

Many thanks

Quan

On Wednesday, December 4, 2019 at 3:15:36 AM UTC+10 martin....@gmail.com wrote:

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