I might be mistaken, but it sounds like the actual location of the sampling point is not important, just the fact that the sample related to a particular polygon.
If this is the case, then I would suggest you do a table join between the Polygon and the Sampling Points using the Polygon ID as the link.
Using this link: https://www.qgistutorials.com/en/docs/performing_table_joins.html
It would be possible to trial it on your datasets.
I am not familiar with the process in QGIS, but using this link you would:
- Right click the polygon layer in the Table of Contents
- Select properties
- In the properties, select joins
- Then select the green plus button in the bottom left of this window
Use the point samples as the input and the IDs of the polygon and point as the joining fields.
I am not sure if the joins are permanent, you may need to export the joined polygon layer out to make it a permanent join.
Start with the Polygon and calculate the coordinate of the centroid of the Polygon. Export the Polygon ID and the coordinates to a CSV File. Open this CSV in Microsoft Excel. Format the Excel Document so that Column A is the PolygonID, B is X and C is Y.
Take your Point File and either export the Attribute Table to CSV or open the DBF. Save this table as an XLS file. Copy the Polygon ID CSV from the step above and save it in Sheet2 of this spreadsheet.
Add two new columns to the sample point file called X and Y. Create a VLOOKUP using the Sample ID as the Lookup field, adding the X and Y values into the associated fields in your Point Table.
So summarising. Your Excel Document will have 2 Sheets. Sheet 1 containing the Point Sample data, with the Sample ID the same as the Polygon ID. Sheet 2 will contain the Polygon ID and coordinates of the centroid coordinates.
In Sheet 1 insert two fields called X and Y into Column B and C.
In Cell B2 of the Sheet 1 use this formula:
In C2 put this formula.
This will give you the X and Y Coordinates of the polygon centroid for that particular sample. Drag the formula down and then save the Excel Doc.
In QGIS create a point file using the Sheet1 coordinates you just calculated above. There should be two points at locations where two samples were taken in the same block.