Shifting existing points (shapefile) to the highest raster pixel value in 5m buffer

Question

I am trying to move 1700 points (of an existing shapefile) to a new pixel of a raster layer. If the dot is already in the highest pixel of the NDVI raster layer then no need to change.

The criteria can be summarized like so:

1. New points need to be on the pixel with the highest NDVI raster value (within 5m buffer)

2. New points should have the same information in the attribute table than the old ones

3. If two points share same pixel because the highest pixel is within their buffer then one of the points should be given the the pixel with the second highest value. Never should two points share the same pixel.

4. Each point should be represented (regardless of being shifted or not) in the new vector layer

I tried a given Code, but not every point was represented in the new layer. It also didn't meet the criteria of being within the 5m buffer (last picture with the orange points).

Answer 1

Here's an approach that will work, but whether it works for you is going to come down to the size of your raster dataset, which you haven't included in the question.

First convert your raster data to vector using say "Raster pixels to polygons". If you have a large dataset this might be problematic.

Then use "Geometry by expression" on your point layer, with the following expression:

with_variable('xy',
    array_sort(
        overlay_nearest('Vector Polygons',
            max_distance:=5,
            limit:=-1,
            expression:=array("VALUE",array(x(centroid($geometry)),y(centroid($geometry))))),
    false)[0][1],
    make_point(@xy[0],@xy[1])
)

This looks complex (and is a bit!). Essentially, it:

1. Gets all the features from the Vector Polygons layer within 5m of each point feature
2. Creates an array of arrays, with one element per feature. The the first element of each sub-array is the value from the raster, and the second element is the (x,y) values of the centroid of each raster point
3. Sorts the array by the value (descending) - you could probably also use array_max instead
4. Takes the first element (the largest value) and stores the (x,y) value in a variable (@xy)
5. Makes a new point using the (x,y) value

You may need to change the layer name ('Vector Polygons') and field name ("VALUE") if your data is different.

Answer 2

There is no straight tool for this, but you can do bit of spatial data processing here. Here are few steps you can try out.

1 - Get coordinates of new locations.

Reclassify raster for greater than 0.8 as 1 everything else as 0. Covert this to polygon (Name it raster_polygon.shp). Calculate geometry (lat long) of centroid in attribute table.

2- fill these latlong to your source point shp.

Create buffer for your points (Name it Point_Buffer.shp). Select Raster_Polygon.shp that intersect with Point_Buffer.shp. Export selected (Name as Raster_Polygon_in_Buffer.shp).

---This will reduce number of polygons created by raster.

Join Point_Buffer.shp and Raster_Polygon_in_Buffer.shp by location (Name it as Raster_Polygon_in_Buffer.shp1). Join this Raster_Polygon_in_Buffer.shp1 and Point.shp (Name this is Point_Moved.shp).

----Hence, you get lat long of new points at center of red pixel (that is where you want to move your points).

3 - Draw point shapefile with new lat long. This will draw points in center of red polygons.