-
Notifications
You must be signed in to change notification settings - Fork 9
/
computeSlope.ca
96 lines (72 loc) · 3.24 KB
/
computeSlope.ca
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
/*
Copyright (c) 2013 Centre for Water Systems,
University of Exeter
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/
// Compute the slope in percent of the central cell using the maximum rate of
// change in value from that cell to its neighbors.
// See http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=How%20Slope%20works
CA_FUNCTION computeSlope(CA_GRID grid, CA_CELLBUFF_REAL_IO SLP, CA_CELLBUFF_REAL_I ELV,CA_CELLBUFF_STATE_I MASK)
{
// Initialise the grid
CA_GRID_INIT(grid);
// Read Mask.
CA_STATE mask = caReadCellBuffState(grid,MASK,0);
// Read bit 0 (false the main cell has nodata)
CA_STATE bit0 = caReadBitsState(mask,0,1);
// If the main cell has no data,
// then do nothing.
if(bit0 == 0)
return;
// Create an array with the elevation values for each neighbourh cell.
CA_ARRAY_CREATE(grid, CA_REAL, GND,caNeighbours+1);
// Create an array with the mak values for each newighbour cell.
CA_ARRAY_CREATE(grid, CA_STATE, MA,caNeighbours+1);
// Create the array which will contain the angle between each cell
// and the main one.
CA_ARRAY_CREATE(grid, CA_REAL, ANGLE, caNeighbours+1);
// Read the elevation and the mask
caReadCellBuffRealCellArray(grid,ELV,GND);
caReadCellBuffStateCellArray(grid,MASK,MA);
// Read the angle of each cell.
caAngleCellArray(grid,ANGLE);
CA_REAL dx = 0.0;
CA_REAL dy = 0.0;
CA_REAL zx = 0.0;
CA_REAL zy = 0.0;
// Loop though the neighbour cell.
for(int k=1; k<=caNeighbours; ++k)
{
// Read bit 0 (false the cell has nodata)
bit0 = caReadBitsState(MA[k],0,1);
// If the cell has nodata set the elevation to be the same of the
// main cell.
GND[k] = (bit0==0)?GND[0]:GND[k];
CA_REAL x = caDistance(grid,k)*caCosReal(ANGLE[k]);
CA_REAL y = caDistance(grid,k)*caSinReal(ANGLE[k]);
dx += caAbsReal(x);
dy += caAbsReal(y);
zx += caStepReal(caAbsReal(x),0.01)*caSignReal(x)*GND[k];
zy += caStepReal(caAbsReal(y),0.01)*caSignReal(y)*GND[k];
}
// Compute Slope
CA_REAL dzdx = zx/dx;
CA_REAL dzdy = zy/dy;
CA_REAL slope = caSqrtReal((dzdx*dzdx)+(dzdy*dzdy));
// Write the are in the buffer
caWriteCellBuffReal(grid,SLP,slope);
}