longitudinal profile of a specific river

[DSKgeo]

Hi, I am trying to extract the longitudinal profile and other indices of a specific river within a basin, which is not the trunk stream. I attempted to do this by providing the coordinates of the headwater of that stream, but when I snap the point to the stream network, it snaps to the nearest stream which happens to be upstream of the point. I want to perform the analysis on the stream downstream of the given point. I am bit new to MATLAB. Could you please help me understand the correct approach and code to use?

[wkearn]

Hi @DSKgeo,

The STREAMobj.modify function with the downstreamto argument might be what you are looking for:

DEM = GRIDobj('srtm_bigtujunga30m_utm11.tif');
FD = FLOWobj(DEM);
S = STREAMobj(FD);

% We need the linear index of the source pixel in the DEM, if you have the
% (x,y) coordinates, coord2ind can get the linear index for you.
IX = coord2ind(DEM,393699,3804210);

S2 = modify(S,'downstreamto',IX);

imageschs(DEM,[],'colormap',[.9 .9 .9],'colorbar',false);
hold on
plot(S,'k')
plot(S2,'r')
hold off

This will also work if you supply vectors of coordinates to coord2ind. In that case IX will be a vector, and the modified STREAMobj will contain all pixels downstream of each of the indices in that vector.

The coordinates you supply need to be part of the stream network already. If they are not, you can extract the downstream flow path from your point using FLOWobj.influencemap and then construct a STREAMobj directly from that flow path:

DEM = GRIDobj('srtm_bigtujunga30m_utm11.tif');
FD = FLOWobj(DEM);

I = influencemap(FD, 393699,3804210);

S = STREAMobj(FD, I);

[DSKgeo]

Thanks a lot for your assistance, @wkearn. It worked.