MRG (version 0.3.21)

MRGoverlap: Function that finds and merges overlapping grid cells in a multi-resolution grid The need for this function comes from an error in the gridding process or how different grids have been stitched together, and it can be seen as symptom solving rather than solving the issue. This function will either just show the problematic grid cells or remove the overlaps.

Description

Function that finds and merges overlapping grid cells in a multi-resolution grid The need for this function comes from an error in the gridding process or how different grids have been stitched together, and it can be seen as symptom solving rather than solving the issue. This function will either just show the problematic grid cells or remove the overlaps.

Usage

MRGoverlap(himg, vars, himg2, action = "sum")

Value

The function will return different objects, depending on "action". The returned object will for different values of "action" be:

none

An sf data.frame with the overlapping grid cells

sum

A multi-resolution grid containing the sum the values of the overlapping grid cells. NAs are ignored unless both cells are NA or one is NA and one is 0

sumna

A multi-resolution grid containing the sum the values of the overlapping grid cells. The sum will be NA if any of them is NA

avg

A multi-resolution grid containing the average of the grid cells. NAs are ignored unless both cells are NA or one is NA and one is 0

avgna

A multi-resolution grid containing the average of the grid cells. The average will be NA if any of them is NA

replace

A multi-resolution grid containing, where the problematic grid cells area replaced with grid cells from himg2

Arguments

himg

A multi-resolution grid, typically resulting from a call to multiResGrid

vars

Variable(s) of interest that should be aggregated (necessary when ifg is used for individual farm specific anonymization rules)

himg2

A multi-resolution grid, typically resulting from a call to multiResGrid

action

How to treat the values of overlapping grid cells. Possible values are:

none

return an sf data.frame just with the overlapping grid cells

sum

sum the values of the overlapping grid cells - NAs are ignored unless both cells are NA or one is NA and one is 0

sumna

sum the values of the overlapping grid cells - sum is NA if any of them is NA

avg

avg of the grid cells - NAs are ignored unless both cells are NA or one is NA and one is 0

avgna

avg of the grid cells - avg is NA if any of them is NA

replace

replace the problematic grid cells with grid cells from himg2

Details

A multi-resoluion grids should not have overlapping grid cells, by definition. However, this could happen through stitching different grids together. Although this should rather have been taken care of during the gridding process, this is not always possible to redo for an end-user.

This function can first of all be used to identify and show the overlapping grid cells. It can also be used to create a valid multi-resolution grid for these cases, as long as the grd cells all have the same base grid (i.e. no overlapping grid cells are partly overlapping, whether the grid cells have the same size or not). However, there will be some additional errors introduced in this process.

Except for action = "none" and action = "replace", the function will try to create a valid grid based on the values in the grid. This means that it has to find a sensible value for the merged grid cells. Frequently one of the grid cells will have an NA value, meaning that it has been suppressed. This means that there are observations in the grid cell, but relatively few. If the overlapping grid cell has a value, this is most likely larger, it is non-confidential. The default action is therefore to sum values, but ignore NA-values unless both are NA or one is NA and the other is 0. The last case means that one of the grid cells have a confidential number of records, whereas the other one has zero records. The total is then a confidential number of records.

if action = "restart", there must be a second grid which includes the updated values of the overlapping grid cells. This could typically happen if the data set is too large to be processed as a single batch. There could then be overlapping grid cells on the border between different batches. Instead of reprocessing the entire grid, it is possible to reprocess the border regions (in one more more batches, as long as they are not overlapping). The grid cells from the border regions have to be passed as himg2.

The function uses st_join to check for overlaps. If the grid has a very high number of grid cells (a few tens of thousands), this process can be rather slow. In that case, it might be better to check parts of the grid separately.

Examples

# \donttest{
library(sf)
library(dplyr)

# These are SYNTHETIC agricultural FSS data 
data(ifs_dk) # Census data

# Create spatial data
ifg = fssgeo(ifs_dk, locAdj = "LL")

ress = c(1,5,10,20,40, 80, 160)*1000
# Create regular grid of the variables, for three regions
ifl = gridData(ifg[ifg$REGIONS %in% c("DK03", "DK04", "DK05"),], vars = c("UAA"), res = ress)
ifl3 = gridData(ifg[ifg$REGIONS == "DK03",], vars = c("UAA"), res = ress)
ifl4 = gridData(ifg[ifg$REGIONS == "DK04",], vars = c("UAA"), res = ress)
ifl5 = gridData(ifg[ifg$REGIONS == "DK05",], vars = c("UAA"), res = ress)

# Create the different multi-resolution grids for different nuts regions
himg3 = multiResGrid(ifl3, vars = "UAA", ifg = ifg[ifg$REGIONS == "DK03",], suppresslim = 0.02)
himg4 = multiResGrid(ifl4, vars = "UAA", ifg = ifg[ifg$REGIONS == "DK04",], suppresslim = 0.02)
himg5 = multiResGrid(ifl5, vars = "UAA", ifg = ifg[ifg$REGIONS == "DK05",], suppresslim = 0.02)

# Bind them together and create new consecutive IDs for the grid cells
himg = rbind(himg3, himg4, himg5)
himg$ID = 1:dim(himg)[1]

# Find the overlapping grid cells, and show some examples.
himgd = MRGoverlap(himg, action = "none")
dim(himgd)
himgd[himgd$ID.y %in% 932:940,]

# Remove overlapping grid cells
himgnew = MRGoverlap(himg, action = "sum")

# Check that there are no more overlaping grid cells
himgd2 = MRGoverlap(himgnew, action = "none")
himgd2


# Create a new multi-resolution grid which has the correct grid cells
# at the border. In this example, the region of interest is so small that
# it is difficult to reprocess just the border grid cells, so 
# we make a new complete grid

himg1 =  multiResGrid(ifl, vars = "UAA", ifg = ifg[ifg$REGIONS %in% c("DK03", "DK04", "DK05"),],
                      suppresslim = 0.02)
himgnew2 = MRGoverlap(himg, himg2 = himg1, action = "replace")
himgd12 = MRGoverlap(himgnew2, action = "none")
himgd12

# }