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When point cloud data is collected,a variety of components are assigned to each individual point include coordinates,intensity,and classification.When creating surface models it is helpful to use point classification to quickly and easily identify ground points to extract the surface model from.In the examples below we will demonstrate how a custom transformer called thePointCloudLASClassifiercreated by a 亚搏在线Safe Software team member can be used within a 亚搏在线workflow to create a DEM or TIN model.
The custom transformer PointCloudLASClassifier can be used to increase the accuracy of a DEM or TIN output by extracting just the ground points.If the point cloud data that you are working with does not have a classification component,then using shapefiles to remove non-ground points,like buildings,can be used.Thisarticleexplains how to this can be done.
To generate correct elevations along point cloud edges,all adjacent point cloud tiles must be taken into account.However,generating a single digital elevation model (DEM) for the center tile and all adjacent tiles can significantly affect performance.To reduce the overall volume of data,we can generate a relatively small buffer around the central point cloud tile and clip the edges of the adjacent tiles with this buffer.The resulting point cloud (the center tile with the edges of adjacent tiles) will be used for making a DEM raster,and then the raster can be clipped to the original extents of the center tile.
a.b.
Image a.shows the original point cloud data with the central tile of interest selected.Image b.is the resulting DEM output from the LAS to DEM 亚搏在线workflow below.
DEMs are commonly used models to represent the surface of the earth.They are raster based models with cell values representing different levels of elevation.Due to each cell being an average representation of the elevation of a surface area,natural landscapes appear smooth,while man-made landscapes appear rough.Creating a DEM from LAS data is quick and simple with FME because you have the ability to use only ground classified points to create your model.
The points within a point cloud have a component called classification.The value of the code within the component represents class like buildings or ground.For creating a DEM we only need the ground class.The steps for creating a DEM from a point cloud are as follows:
Optional: Try running the workspace without the link from the PointCloudLASClassifier transformer to the RasterDEMGenerator and instead connect the "Split" points from the PointCloudSplitter.Compare the different output DEMs.
a.b.
Image a.shows the what the DEM output looks like when all points are used in the 亚搏在线workflow to create a DEM.Image b.Is what the DEM looks like when only the ground classified points are used.Using only the ground classified points creates a much smoother and realistic representation of the ground itself.
If using other LAS files to generate a DEM,check to see if the points come with classification.If so,make sure that only appropriate classes are used for DEM generation.
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The best results for creating a surface model with buildings can be achieved when a point cloud has a classification component.We can use the Data Inspector orPointCloudPropertyExtractorto check whether this component exists.If the point cloud has a classification of 2,the ground,it is often enough for generating surface.However,excluding buildings can still help to make a more precise model as it can help avoid classification errors.Thisarticleexplains more about splitting points cloud by class.The steps for this workspace are as follows:
The output from this workspace is much smoother.Note that the bridges have disappeared from the model.This means that they have some other classification rather than ground:
This workspace generates a TIN (as a 3D PDF file) using a DEM as a texture:
hi Mita
I triedLAS_to_Textured_TIN_FME2011.fmwtand it gave me blank PDF after 14 minutes running.what am i missing here?can u advise please.
@heikalIt's hard to say without looking at your data/workspace.Note that the workspace is reading in tiles and then doing some processing on them in the workspace.Are you also reading tiles?Does the log report any errors/warnings?We have a debugging guide that should helphttps://knowledge.亚搏在线safe.com/articles/19301/root-cause-analysis-guide.html
Hi there
I tried your las to DEM and I got "Translation was SUCCESSFUL with 1 warning(s) (0 feature(s) output)
FME Session Duration: 24 minutes 52.7 seconds.(CPU: 1489.6s user,1.1s system)
END - ProcessID: 5428,peak process memory usage: 1322008 kB,current process memory usage: 50552 kB
Translation was SUCCESSFUL"
However,I can not display the results,Any advice?
regards
Please find attached my *.fmw filemita-las-to-dem.fmw
I appreciate any advice and recommendation
Hi@heikalThe log is saying you have "0 features output".There are transformers in your workspace that need to be connected,and also that don't have their properties set.I suggest removing everything but the RasterDEMGenerator and see if that works,at a minimum.If you are still having problems please send along your workspace and source data to our support teamhttps://support.亚搏在线safe.com/knowledgeSubmitCase
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