| Bounding [message #17704] |
Tue, 09 November 1999 00:00  |
Lazzar
Messages: 9
Registered: February 1999
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Junior Member |
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I am looking for some help with interpolating a surface from ungridded
data points. I have several thousand measurements in a river with
corresponding latitudes and longitudes for each of the points. I would
like to make a surface of these data, but have run into a small
problem. I have been using a combination of TRIANGULATE and TRIGRID to
grid the data into a surface, however I end up with data being
interpolated outside the bounds of the river. Is there any way to bound
the resulting grid to only include data within the river banks? Also,
is there any way to determine a variance associated with the
interpolation?
Thanks for any help you can provide,
Brian
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| Re: Bounding [message #17742 is a reply to message #17704] |
Fri, 12 November 1999 00:00  |
Michael Asten
Messages: 53
Registered: March 1999
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Member |
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Brian wrote:
> I am looking for some help with interpolating a surface from ungridded
> data points. I have several thousand measurements in a river with
> corresponding latitudes and longitudes for each of the points. I would
> like to make a surface of these data, but have run into a small
> problem. I have been using a combination of TRIANGULATE and TRIGRID to
> grid the data into a surface, however I end up with data being
> interpolated outside the bounds of the river. Is there any way to bound
> the resulting grid to only include data within the river banks?
Ive seen it done very efffectively using a mask on the grid . As I recall
the logic used was like this (pseudo code ).
gridded data is n points in vectors xgrid,ygrid,zgrid
raw data is m points at locations given by vectors xdata,ydata
cell_size is length of edge of grid cell
no_value =-1.e10 ; is a flag value which is ignored when contouring
dmin=fltarr(n)
for i=0,n-1 do begin
d= sqrt( (xgrid(i)-xdata)^2 + (ygrid(i)-ydata))^2 ) ; vector length m
of distances
dmin(i)=min(d)
endfor
b=where(dmin gt cell_size) ; grid points which are too far from any
measurement point
if b[0] ne -1 then zgrid[b]=no_value ; kill them
contour,zgrid,xgrid,ygrid,min_value=-1.e9
end
Ive been meaning to implement it for some time. I'll be interested to know
whether
Ive got the logic right.
Regards,
Michael Asten
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