# RiHydro Workflow

RiHydro performs refraction correction of bathymetric points. Before refraction correction can be accomplished, a water surface must be created. Additionally, it's necessary to classify noise and water surface points.

## Classify Noise

First, classify noise points. You can access the Point Classifier from the Tools menu.

Select the Isolated Point Classifier method. You can modify the point classification parameters by clicking the wrench icon. In most cases, the default count of 5 neighbors within 5 meters parameter works well:

<figure><img src="/files/MI40AVHvBtOi5wVoicHh" alt=""><figcaption></figcaption></figure>

Select the Laser Data records which you wish to process, then click OK.

View the point classification and ensure that noise has been classified correctly.&#x20;

## Classify Water Surface Points

After noise has been classified, you can classify water surface points. These water surface points will be used to create the water surface model.&#x20;

The default water surface classifier uses information from an infrared lidar channel. The HydroRanger does not have this channel, so it's necessary to make a water surface point classifier that uses the green channel (532 nm):

<figure><img src="/files/yfovw0GoCxkVUUsI9LYV" alt=""><figcaption></figcaption></figure>

Select your laser records and click OK.&#x20;

Once the classification is complete, view the result in the 3D view. Ensure all isolated noise is classified correctly and that water surface points have been classified on the water surface.&#x20;

<figure><img src="/files/WB2LdGmPLRQqekuynUAZ" alt=""><figcaption></figcaption></figure>

{% hint style="info" %}
It's acceptable to have some points on the water surface which are NOT classified as water surface points (in this case, white). However, if water surface points were classified on non-water surfaces (i.e. water surface points classified on the ground), this is an issue, and the filters should be modified and re-executed.&#x20;
{% endhint %}

## Create Water Surface Model

Navigate to Tools-> RiHydro -> Create Water Surface Model. Select your laser data records and run the tool with default settings:

<figure><img src="/files/vZW8EJTuRV6lotuV3z1s" alt=""><figcaption></figcaption></figure>

## Execute Refraction Correction

With the water surface created, navigate to Tools-> RiHydro -> Execute refraction correction.

Set modified points to class 066 - RIEGL Underwater Points. The settings below work well for fresh water:

<figure><img src="/files/RRqDjDb69RDkKmjhw12M" alt=""><figcaption></figcaption></figure>

Salt water applications should use the calculator icon to compute refractive index and depth bias correction:

<figure><img src="/files/emRIqt3mFahVmA1f9hGP" alt=""><figcaption></figcaption></figure>

Select your laser data and click OK to execute the tool.

You should now be able to see bathymetric points classified accurately. It's not uncommon for the shoreline to be classified as bathymetric surface, due to its close proximity to the water surface:

<figure><img src="/files/kZz8wuEbwm2IHOWVg8oO" alt=""><figcaption></figcaption></figure>


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