To add to this, WAAS uses a combination of ground based equipment and geostationary satellites.
The ground based equipment is responsible for detecting the necessary corrections, which are then sent up to the WAAS satellites which will in turn broadcast those corrections.
Unlike GPS satellites, WAAS satellites are always located over North America due to the fact that they are in a much higher, geostationary orbit.
Edit - WAAS also provides GPS-based vertical navigation (e.g. descent profile in an approach) - IIRC this is due to the fact that the ground station transmit accurate atmospheric pressure readings up to the geostationary satellites, then the GPS receiver in the aircraft can use those to adjust altimeter readings. GPS-based vertical navigation is a big deal, because many airports don't have systems such as ILS.
WAAS (and other SBAS constellations) are used for RNAV/RNP LPV approaches indeed (for both lateral and vertical navigation), but WAAS is only used to obtain atmospheric corrections for the GPS signals, the WAAS ground stations do not transmit atmospheric pressure. Furthermore, unlike GBAS (Ground Based Augmentation Systems), SBAS ground stations are not located at the airport, they can be dozens or hundreds of kms away making the atmospheric pressure from there not very useful.
Thank you for clarifying, I wasn't sure about that part. Good link! The diagram is very clear. Basically WAAS allows us to triangulate the vertical position of the aircraft. So as you pointed out, it's not related to pressure readings.
The cool part for me was realizing that the three WAAS satellites not only broadcast the correction signals but also act as position / constellation satellites! This adds an additional 2-3 satellites to the "currently visible" mix and helps ensure high availability location data at all times over the continental US.
The ground based equipment is responsible for detecting the necessary corrections, which are then sent up to the WAAS satellites which will in turn broadcast those corrections.
Unlike GPS satellites, WAAS satellites are always located over North America due to the fact that they are in a much higher, geostationary orbit.
Edit - WAAS also provides GPS-based vertical navigation (e.g. descent profile in an approach) - IIRC this is due to the fact that the ground station transmit accurate atmospheric pressure readings up to the geostationary satellites, then the GPS receiver in the aircraft can use those to adjust altimeter readings. GPS-based vertical navigation is a big deal, because many airports don't have systems such as ILS.