Visualizing Dense Areas in cartesian plane

I have a table that contains x, y coordinates (cartesian)of a large number of points. X coordinates are stored in a column called sp_x and corresponding y coordinates are stored in the column named 'sp_y'.

I download these data to matlab (please see the following coding) and assign x, y values to a matrix called xy. Now I want to see the dense areas (areas where the point density is high). Does anybody know a way to do this? pls help.

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curs1 = exec(conn, 'select sp_x, sp_y from road_part6_trajectories_oneway2_new_segments_cartesian2');

format long;

curs1 = fetch(curs1);

r=rows(curs1);

AA = curs1.Data;

x = [AA{:,1}]';

y = [AA{:,2}]';

for i=1:5

      xy(i,1)=x(i);

      xy(i,2)=y(i);

end;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Answer 1

[Walter Roberson]

xpnts = 100;  %set as desired
ypnts = 100;  %set as desired

minx = min(x);
miny = min(y);
scalex = xpnts ./ (max(x) - minx);
scaley = ypnts ./ (max(y) - miny);

scaledx = 1 + floor(x-minx) * scalex;
scaledy = 1 + floor(y-miny) * scaley;

densemap = accumarray([scaledx(:),scaledy(:)],1);
imagesc(densemap);

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[Devinya Herath]

I am sorry. I get the following error message.

??? Error using ==> accumarray

First input SUBS must contain positive integer subscripts.

Error in ==> temp12 at 28

densemap = accumarray([scaledx(:),scaledy(:)],1);

[Walter Roberson]

Ah, floor()'d at the wrong place. Please use

scaledx = 1 + floor((x-minx) * scalex);

scaledy = 1 + floor((y-miny) * scaley);

[Devinya Herath]

Again, I get the following error. In my program xpnts=576078 and ypnts=576078 Is this the cause? If so what is the solution for that. Pls help.

??? Error using ==> accumarray

Maximum variable size allowed by the program is exceeded.

Error in ==> temp12 at 28

densemap = accumarray([scaledx(:),scaledy(:)],1);

[Devinya Herath]

Yes. The program does work if xpnts and ypnts are smaller than 9000. If they are larger, I get the above error.