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1
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/* using srtmv41 3x3 degree patch smoothed to srtmv41_smth
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2
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3
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&describe srtmv41_smth
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4
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&sv cellsize %grd$dx% * 111000
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5
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dzdx = (srtmv41_smth(1,0) - srtmv41_smth(-1,0)) / (2 * %cellsize% * cos($$ymap / deg))
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6
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dzdy = (srtmv41_smth(0,-1) - srtmv41_smth(0,1)) / (2 * %cellsize%)
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7
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slope = sqrt(sqr(dzdx) + sqr(dzdy))
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8
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slopedeg = atan(slope) * deg
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9
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/* use scaling factor that is average of x and y scaling factors, 0.707 and 1 ~= 0.85
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10
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/* and 0.85 / 111000 ~ 0.0000107
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11
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arcslope = slope(srtmv41_smth, 0.0000107, degree)
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12
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hillshade = hillshade(srtmv41_smth, 300, 30, shade, 0.00001)
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13
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14
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aspect1 = atan2(0 - dzdy, 0 - dzdx) * deg
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15
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aspect = con(aspect1 > 90, 450 - aspect1, 90 - aspect1)
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16
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kill aspect1
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17
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18
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/*use elevation
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19
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flowdir = flowdirection(srtmv41_smth)
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20
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21
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/*cell area to account for latitudinal area effects, smallest area near pole
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22
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setwindow srtmv41_smth
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23
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setcell srtmv41_smth
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24
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cellarea = sqr(%cellsize%) * cos($$ymap / deg)
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25
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flowacc = flowaccumulation(flowdir, cellarea)
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26
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27
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/*account for sinks
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28
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/*change # defaulto z limit
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29
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/*caution fill is a command not function
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30
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/*fill srtmv41_smth srtmv41_fill sink # flowdir_fill
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31
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32
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flowacc_fill = flowaccumulation(flowdir_fill, cellarea)
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33
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34
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/*scatch_fill is specific catchment area in m
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35
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scatch_fill = flowacc_fill / sqrt(cellarea) + sqrt(cellarea) / 2
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36
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/*setting the min slope to 0.1
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37
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adjslope = tan(max(slopedeg, 0.1) / deg)
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38
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39
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twi_fill = ln(scatch_fill / adjslope)
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