Is there anyway to Re-grid one dataset to another dataset resolution without interpolating??
조회 수: 2(최근 30일)
Hey everyone, I have a geographical data (A) of dimension (120(lon) × 90(lat)) whose longitude (start=-178.5, end=178.5) resolution is 3 deg and for lat (start=-89, end=89) is 2 deg.I want to Re-grid this data to a different dimension of (720×360) (whose lat_start=-89.75,lat_end=89.75 and lon_start=-179.75, lon_end=179.75) whose lat and lon resolution is 0.5 deg without interpolating. Without interpolating means I want to put original data (A) every point to the closest of the new resolution (lat,lon), otherpoints I want to put zero or NaN. So the new matrix will have new dimension (720 × 360).
Walter Roberson 2021년 8월 2일
norlon = length(origLon); norlat = length(origLat);
A = rand(norlon,norlat);
nnlon = length(newLon); nnlat = length(newLat);
lonbin = interp1(newLon, 1:nnlon, origLon, 'nearest');
latbin = interp1(newLat, 1:nnlat, origLat, 'nearest');
B = nan(nnlon, nnlat);
B(lonbin, latbin) = A;
John D'Errico 2021년 8월 3일
편집: John D'Errico 2021년 8월 3일
What you are asking to do is arguably still "interpolation" of a sort. In fact, Walter''s use of nearest neighbor is quite reasonable.
At the same time, what you are asking to do is really laughably trivial to accomplish, just using a simple index rescaling. For example:
A = rand(4,3)
Now, suppose I want to "regrid" this onto a 9x7 grid, inserting NaNs wherever necessary.
OldSize = size(A);
NewSize = [9,7];
B = NaN(NewSize);
[indr,indc] = ndgrid(1:OldSize(1),1:OldSize(2));
% convert to the new indexing
indr = 1 + round((indr-1)*(NewSize(1)-1)/(OldSize(1)-1));
indc = 1 + round((indc-1)*(NewSize(2)-1)/(OldSize(2)-1));
B(sub2ind(NewSize,indr,indc)) = A
The result here is a bit coarse, with either 1 or 2 NaNs inserted in some rows as needed.
This will work of couse as long as the new grid is larger than the old one. If it was smaller, then you have a serious problem, one that cannot be resolved directly using any such scheme. But then you would need to decide what it means to regrid onto a smaller grid. You might decide to average elements that end up in the same boxes. This is itself doable, using tools like accumarray.