# Merging surveys

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## Merge surveys

The operation of merging surveys is applicable in the following cases:

- The geometry of one or more reference parcels in one field has been updated by one or more separate CAPI surveys.
- The updated geometry comes from field surveys (GNSS).
- The updated geometry comes from reliable third party data (mapping agency, road authority, etc.).

This process generates a new polygon and thus a potentially a new reference area. Before updating that reference area, the 2% stability rule has to be applied.

*Figure 16: Merge surveys*

The method recognizes the following steps

- As usual, start by retrieving the documented anomaly and analysing the description.
- NOTE. When the update process is performed in one go (i.e. all the use cases are performed one after another), this step can be omitted, since all workflows were driven by the same anomaly and the operator is likely to know the anomaly description very well.
- Retrieve the reference orthoimage and put it as a background to display with the rest of the information.
- Retrieve the survey data and overlay it with the reference orthoimage.
- Retrieve the reference parcel geometry subject to editing and overlay it with the reference ortoimage and survey data. Check the right reference coordinate system. Reference parcel is now ready for perimeter editing.
- Perform the congruency test whenever a coordinate shift is apparent between any of the data sources (reference parcel, image, new survey), perform the congruency test as described above, always considering the RP vector as reference.
- Determine the coordinate shift between the new survey and those present in LPIS and apply the correction to the coordinates of the imager and/or new survey before inserting the new geometry in LPIS.
- Insert the new parcel geometry in LPIS by replacing any old perimeter segment with corresponding, locally corrected new survey segments.
- Calculate the area of the resulting reference parcel polygon.

The series below illustrates how a segment of RP boundary, measured with field survey, is inserted in the reference parcel perimeter. Procedure ensures that all data involved respect the homogenous standard of the LPIS.

In order to proceed with merging all input data has to be in the same coordinate reference and projection system. When this is not the case some of the input data has to be translated. | |

The same georeferencing process has to be performed for the newly surveyed boundary section too. | |

Insertion of new geometry segment: The dangling segments beyond confirmed primary vertices are removed from both original perimeter and new survey vector. |

*Figure 17: Illustration of the merger of surveys*

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