| A new puzzle for histogram [message #50147] |
Fri, 15 September 2006 15:07  |
gknoke
Messages: 9
Registered: September 2006
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Junior Member |
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So, I've got this piece of code which is horribly horribly inefficient.
I know the solution lies in a clever application of the histogram
function, but being Friday afternoon my brain isn't seeing it. Anyone
else have any insight on how I might approach it?
This particular routine is mapping a piece of data from polar to
cartesian coordinates. Currently the code generates sin/cos angle
tables and calculates the x,y coordinates in meters for each
range/angle, and then converts that to an x,y coordinate in terms of
pixels from the center. I realize the calculation of the x,y
coordinates can be replaced with a simple vector operation, but I can't
see how to turn the separate resulting arrays for x and y into a single
array I can use the histogram function to match to the mapped grid.
;Setup the output grid
map = fltarr(xysize, xysize)
count = intarr(xysize, xysize)
cos_table = cos(angles)
sin_table = sin(angles)
for j_theta = 0, n_elements(angles)-1 do begin
for i_range = 0, n_range-1 do begin
;Calculate x and y in meters
x = r_pts(i_range)*cos_table(j_theta)
y = r_pts(i_range)*sin_table(j_theta)
;Find corresponding pixel on mapped grid
ix = round((x-x0)/cellsize)+xysize/2
jy = round((y-y0)/cellsize)+xysize/2
;If the pixel coord is inside the image put the data point there
if(ix ge 0 and ix le xysize-1) then begin
if(jy ge 0 and jy le xysize-1) then begin
map(ix,jy)=map(ix,jy) + data(i_range,j_theta)
count(ix,jy)=count(ix,jy)+1
endif
endif
endfor
endfor ;End of nearest neighbor loops
Thanks,
--Greg
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