Keeping a global accuracy along multiple surveys can be difficult if there is no preparation. The purpose of this article is to give recommendations while creating your high precision project on Alteia to avoid shifts during the project lifetime, survey after survey.

1 - Choosing the CRS

This first recommendation is the most crucial one. To avoid any shift between the customer historical/control data, it is very important to choose the correct CRS during the Site creation. Please choose the same CRS than the historical/control dataset. If there was no CRS, privilege WGS84/ local UTM for the horizontal CRS and WGS84 ellipsoid for the vertical CRS.

2 - Historical Data

Having an historical topographic plans such as rasters or vectors can be very handy while creating a new Site on Atleia. Those datas can be used to set the CRS and also to compare Alteia’s deliverable to the actual physical site. Please do look if there is any historical data and also any reference point on which the coordinates is precisely known in the CRS of this historical data. If there is no reference point please create one and take its coordinate in the previously chosen CRS.

3 - GCP

• Please follow the distanciation rules, numbers, placement about GCP Best practices.
• Make sure to use the same CRS as the one used for the site creation and most importantly use the historical reference point to position your GCP base station.
• In case the physical Site is not accessible, add a point outside of the physical site that can be used as GCP to readjust an RTK of PPK flight.

4 - PPK and RTK flight

• Make sure to use the known reference point of the historical data as a reference point to put the base station of the RTK/PPK system.
• Do not forget to take into account your antenna height.