h1. HT2 - Create a Digital Terrain Model from a T-Lidar point cloud

|{width:4000px;text-align:left;border-color:transparent}. !/attachments/download/19/fr_FR.png! [[Fr_extractSoil|...version française de cette page]] |

notice<>. This tutorial uses the following script in the *Computree* *HowTo* subfolder: _HT2_Create_DTM.xsct2_

h2. Objectives

p<>. This tutorial shows how to :
# _Open a point cloud_
# Add the DTM creation step
# Configure the tool parameters
# _Export the model in a raster format_

h2. Open a ploint cloud

Please refer to tutorial [[En_loadCloud_|HT1 - Load, visualize, crop and export a T-Lidar point cloud]].


h2. Add the DTM creation step

The  _OE_StepExtractSoil03_ step is found in the *onfensamv2* plugin.  This step distinguishes ground points from vegetation points and generates:
* a Digital Terrain Model (DTM)
* a Digital Surface Model (DSM)
* a Digital Height Model (DHM)

To add a step, right click on the previous one and then select the tool. Select the  *onfensamv2* plugin, and then the *Soil / vegetation segmentation -> DTM* step.

!OE_StepExtractSoil03_EN.jpg!

h2. Tool parameters configuration

Tool steps and parameters:

* A Zmin grid is created at the specified *Grid resolution*. The resolution must be in centimeters. The same resolution will be used for the output models.

notice<>. A 50 cm resolution is suitable for a moderate slope plot. For a steeper slope, a finer resolution is recommended.

* Point density is calculated for points located between Zmin and “Zmin + *Soil thickness*”.

notice<>. The Soil thickness parameter depends on the grid resolution. The larger the pixels are, the greater the parameter value must be, so that all ground points are included.

* NULL value is given to the grid's pixels that have a point density smaller than the *Minimum density*.
* If the *Interpolation* box is checked, NULL values ares replaced by the average of natural neighbors.
* If the *Smoothing* box is checked, each cell is transformed according to the K-Nearest Neighbor (k-NN) method. K (*Neighborhood* in number of pixels) must be specified.

!config_OE_StepExtractSoil03_EN.jpg!

Here is an exemple of a Digital terrain Model (DTM):

!MNT.jpg!

h2. Export the model in a raster format

Please refer to tutorial [[En_loadCloud_|HT1 - Load, visualize, crop and export a T-Lidar point cloud]].

tip<>. The  *Grilles 2D, ASCII ESRI Grid* format is recommended.

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