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How to create breaklines for LiDAR Data? Error in height(DSM-DEM) with water bodies

SamriddhiShakya

Hi everyone ,

I have liDAR data (LAS files) of a county and I want to calculate height of the features from it . I created multi-points for both bare earth and non-ground and also terrain dataset from it.However , I do not have the breaklinesfor my LiDAr data .From the terrain dataset ,I created DEM and DSM Raster and also got the height raster(DSM-DEM) of the features from it. However , I am having some errors with the height of some water bodies .Normally,water bodies does not have much height but I am having some water features having more that 10 to 20 meters of height .

When I checked for the error,I found that while making Terrain dataset ,the height of water features have been overestimated. Since I don't have breaklines for my data to seperate water features, I am not able to eliminate this error . Is there anyway that I can solve this problem or create the break-lines for my liDAR data.

Waiting for your kind response.

Thanks ,
Sam

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Accepted answers

XanderBakker

Hi Sam,

In your case it would be better to use polygons with a single height linked to it. If you look at the Help topic "Fundamentals of creating TIN surfaces" you will see at the Polygon surface feature types section:

Replace polygons set the boundary and all interior heights to the same value. A replace polygon could be used to model a lake or an area on a slope excavated to a level surface.

... which is what you want.

If you look at the explanation of "Hard breaklines" in the section Breaklines and hulls, you will see:

Hard breaklines represent a discontinuity in the slope of the surface. Streams and road cuts could be included in a TIN as hard breaklines. Hard breaklines capture abrupt changes in a surface and improve the display and analysis of TINs.

See also this topic on Breaklines in surface modeling which visually explains how breaklines work.

Kind regards,

Xander

All comments

XanderBakker

Hi Samriddhi,

There is a Help topic called "Incorporating breaklines with lidar". You will still need to have polygons that outline the waterbodies to correct the error.

Kind regards,

Xander

SamriddhiShakya

Hi Xander,

Thanks for the reply . I have already gone through the ArcGIS Help "Incorporating Breaklines with Lidar" . The problem is that I don't have the the polygons for my water bodies . Since my work is related to isolated wetlands of Lee county which have not been documented properly in maps,I do not have break-lines for them . Is there anyway that i can create breaklines for these water bodies ? Do I have to individually digitize each of the water bodies ? Is there any other way that i can eliminate the error of water bodies not having heights?

Regards ,

Sam

XanderBakker

Hi Sam,

I see what you mean. That would be a lot of work. What other kind of information do you have in your LAS file (RGB, Intensty, returns, ?). This might be useful to detect those points that need correction. Otherwise, I think there should be some data source somewhere that could be helpful, right?

Kind regards,

Xander

SamriddhiShakya

Hi Xander ,

Ya , it will take me lot of time if i had to digitize individually each water body . My LAS data has information of intensity ,return number , number of returns,scan direction , color red , color green ,color blue etc. Can you please explain me how these information will be helpful and how i can apply it to minimize my error .

I am sure there must be data for breaklines with others but I don't know whom to contact and from where to get the data

Thanks ,

Regards ,

Sam

XanderBakker

Hi Xander ,

Ya , it will take me lot of time if i had to digitize individually each water body . My LAS data has information of intensity ,return number , number of returns,scan direction , color red , color green ,color blue etc. Can you please explain me how these information will be helpful and how i can apply it to minimize my error .

I am sure there must be data for breaklines with others but I don't know whom to contact and from where to get the data

Thanks ,

Regards ,

Sam

Hi Sam,

The reason I ask this, is that different features will behave differently. If you have more information per LAS point, this will help in trying to distinguish between the wetlands and other features. If you have the LAS dataset toolbar in ArcScene you could symbolize on each of those characteristics like Class, Return, Intensity or RGB. In case you can visually distinguish those features, you may be able to instruct the computer to do that also.

These LAS attributes can be converted to raster format using:
LAS Point Statistics As Raster (Data Management)
or
LAS Dataset To Raster (Conversion)

The resulting rasters can be used with some Raster Calculations or maybe even in a "Maximum Likelihood Classification (Spatial Analyst)" or a supervised classification (see An overview of the Image Classification toolbar).

Kind regards,

Xander

larryzhang1

...

Is there anyway that i can create breaklines for these water bodies ? Do I have to individually digitize each of the water bodies ? Is there any other way that i can eliminate the error of water bodies not having heights?

...

Sam,

Ideas as alternative solutions to get water boundary:

If a very-high-resolution raster image with NIR band covering AOI (saying, satellite image like 0.6-m QUICKBIRD/0.5-m GeoEye or 0.25-m airphoto) available to you, it would help automatically �??extract�?? boundary of water bodies (lakes, reservoir, etc.), which usually can be done simply via �??Threshholding�?? and then conversion into polygons.

Besides, on LAS format standard 1.1 or higher, Lidar cloud points can be classified into a number of categories including �??water�??. If you don�??t see this water catalog in LAS files, you still have a chance to ask LAS data provider to re-classify by their LiDAR package (saying, TerraScan).

++++++++
Note,

Extracting the boundary of water /trees from raster image is much easier than other features (buildings, roads, etc). Generally, users need not use advanced classification algorithms like object-oriented feature extraction. Read the discussion at http://forums.arcgis.com/threads/91921-Raster-to-Polygon-NOT-WORKING?p=326538&viewfull=1#post326538

SamriddhiShakya

Hi Everyone ,

Sorry for the late reply . I got the break lines for the Lidar data but I am not getting what i expected .I built a terrain dataset in which I included my non-ground multipoint(Mass point) and hydro break line(hardline) . I got a new terrain in which the water bodies did not have smooth flat terrain surface but instead had spikes and varying elevation . I have attached the image of the water body surface of my terrain dataset[ATTACH=CONFIG]29230[/ATTACH].

Can you please help me where i got it wrong or send me good link so that i can improve my output.

Waiting for your kind response.

Sam

terraindataset.JPG

XanderBakker

SamriddhiShakya

Hi Xander ,

Thanks for the links . It helped solve my problems . I used the replace polygon while creating the terrain and it helped solve my problem . The water bodies are flat now.

Thanks for the help. I really appreciate it .

Sam

XanderBakker

Hi Sam,

If you think the answer was helpful you can use the "arrow" button in order to help other members find useful information:

More info here: http://resources.arcgis.com/en/help/forums-mvp/

Kind regards,

Xander

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