Bentley Descartes Ground Extraction

Hi Anthony,

The Ground Extraction tool works in 3 steps.

1) The value of the "Largest Infrastructure Size" setting is used to create a grid over the Reality Model (Reality Mesh or Point Cloud). The grid's tiles must be big enough that each tile contains at least one ground point. Ground points (called "Seed Points") are found in each tile and a TIN is computed from those points. To validate seed points, output them to a DGN level by selecting the "Seeds" output method.

2) The second step consists of iteratively refining the TIN created in the first step. The "Terrain Variation" setting influences the number of iterations. A smaller value will create a flatter terrain. Getting this setting right may require a bit of trial and error.

3) Once the TIN refinement is completed:

-If the user has chosen to output a "Terrain", the Geopak .Tin file is created and an STM is automatically generated.

-If the user has chosen to output a "Classified Point Cloud" then a threshold is used to classify all points of the point cloud that is within that distance from the TIN surface to the "Ground" class. (When the input is a Reality Mesh, a Point Cloud is automatically created and classified.)

One last thing that can influence the result. When working with a reality mesh, the model’s resolution is determined by the “Export Resolution” setting.

To change this setting:

1. Select a reality mesh attachment.
2. Open the "Properties" dialog.
3. Navigate to the "Reality Mesh" section.

Hope this helps. Don't hesitate to ask if you have more questions.

Pascal

Awsome! Thanks for the help I'm still a bit confused on the Largest Infra size tho. Do you just measure vertical with a building or horizontal? Also once you create a terrain model how do you change the contour lines? Meaning if it's default is a contour line every 1 foot then how do I change that to every inch for example? Last question is how did you get the information? Did you read it from somewhere? Tutorial? And I lied....this is the last question What is Max. Triangle Edge? Does it effect the ground and created classification? Thanks again.

Anthony,

I'll try to answer your questions one at a time.

I'm still a bit confused on the Largest Infra size tho. Do you just measure vertical with a building or horizontal?

Answer: You should measure the smallest side of the largest man-made infrastructure in the model.

Also once you create a terrain model how do you change the contour lines? Meaning if it's default is a contour line every 1 foot then how do I change that to every inch for example?

Answer: Select the Scalable Terrain Model and open the "Properties" dialog. In the dialog's top pane, navigate to: Elements > Scalable Terrain Model > Calculted Features > Contours. Select the "Contours" node, in the properties area, fields named "Major interval" and "Minot Interval" are available to change the contour spacing.

Last question is how did you get the information? Did you read it from somewhere? Tutorial?

Last Answer ;) : I'm a Product Engineer on the team that develops Descartes. I got the information straight from the source. We will look for ways to create material to better explain this.

And I lied....this is the last question What is Max. Triangle Edge? Does it effect the ground and created classification?

Answer: When the TIN is refined, the triangles become smaller and smaller. Max triangle Edge is a parameter that is used to stop the iteration. When a triangle's edge is smaller than this value, it is no longer refined. Classification on the other end is controlled by the "Threshold" value. All points that are between the refined TIN's surface and this value are classified as ground.

Thanks for your feedback,

Pascal

Anthony,

I'll try to answer your questions one at a time.

I'm still a bit confused on the Largest Infra size tho. Do you just measure vertical with a building or horizontal?

Answer: You should measure the smallest side of the largest man-made infrastructure in the model.

Also once you create a terrain model how do you change the contour lines? Meaning if it's default is a contour line every 1 foot then how do I change that to every inch for example?

Answer: Select the Scalable Terrain Model and open the "Properties" dialog. In the dialog's top pane, navigate to: Elements > Scalable Terrain Model > Calculted Features > Contours. Select the "Contours" node, in the properties area, fields named "Major interval" and "Minot Interval" are available to change the contour spacing.

Last question is how did you get the information? Did you read it from somewhere? Tutorial?

Last Answer ;) : I'm a Product Engineer on the team that develops Descartes. I got the information straight from the source. We will look for ways to create material to better explain this.

And I lied....this is the last question What is Max. Triangle Edge? Does it effect the ground and created classification?

Answer: When the TIN is refined, the triangles become smaller and smaller. Max triangle Edge is a parameter that is used to stop the iteration. When a triangle's edge is smaller than this value, it is no longer refined. Classification on the other end is controlled by the "Threshold" value. All points that are between the refined TIN's surface and this value are classified as ground.

Thanks for your feedback,

Pascal

Thanks! Is there any way I can get your contact information? I've been trying to decide between CC and Pix4D as what we are going to use for processing drone images. I'd like to have a good contact with Bentley that knows what they are talking about. Thanks!