# Upkeep - Merging surveys

From Wikicap - European Commission

SECOND DRAFT

## Introduction

This article describes a reference parcel perimeter can be constructed from components that originate from separate survey activities. It allows merging perimeter parts from

- two different CAPI surveys
- a CAPI and GNSS survey

Merging perimeter parts that originate from two separate GNSS surveys is considered straightforward and not in the scope of this article. As a result there is always at least one background orthoimage involved.

This guidance goes beyond the earlier guidance available on combining Field and CAPI methods during OTSC area measurements]

## Procedure

This instruction detail action BP0110001 of the model.

**figure 3di.1**: activity diagram for merging surveys

Follow these steps to ensure the relative accuracy of all sources is maintained.

- Identify the reference parcel subject to perimeter editing.
- Identify the reference orthoimage to serve as background.
- Perform the procedure to determine the shift of the LPIS parcel vectors and the reference orthoimage. The test returns a local translation vector between the LPIS vector and the reference image.
- Make a local correction on the reference image to perfectly georefence with the parcel (i.e. shift the image to exactly compensate the result of the congruency test}.
- Perform the congruency test between the newly surveyed part of the perimeter and the locally corrected image from the previous step to determine the coordinate shift between that new survey and the locally corrected image.
- Make a local correction of the coordinates of the new survey to exactly compensate for the shift found during the second congruency test.
- Replace the old perimeter segment with the locally corrected new survey segment.
- Connect the newly surveyed part with the remainder of the perimeter, but only between the closest primary vertices (i.e. visible on the reference image) of each component.
- Calculate the area of the resulting polygon with your GIS software.
- For type I and III changes, check if the new area is significantly different.

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