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2. PTKERNEL2D procedure

PTKERNEL2D procedure

Performs kernel smoothing of a spatial point pattern (M.A. Mugglestone, S.A. Harding, B.Y.Y. Lee, P.J. Diggle & B.S. Rowlingson).

Option

`PRINT` = string tokens What to print (`grid`, `monitoring`); default `grid`, `moni`

Parameters

`Y` = variates Vertical coordinates of each spatial point pattern; no default – this parameter must be set Horizontal coordinates of each spatial point pattern; no default – this parameter must be set Vertical coordinates of each polygon; no default – this parameter must be set Horizontal coordinates of each polygon; no default – this parameter must be set What kernel width to use for each pattern; no default – this parameter must be set Numbers of rows to use in the grid of kernel density estimates; default 20 Numbers of columns to use in the grid of kernel density estimates; default 20 Variates to receive the vertical coordinates at which each kernel function has been evaluated Variates to receive the horizontal coordinates at which each kernel function has been evaluated Matrices of dimension NY by NX to receive the grid of density estimates

Description

This procedure performs kernel smoothing of a spatial point pattern using the methods of Diggle (1985) and Berman & Diggle (1989). The kernel density estimate at a point (x, y) represents the intensity of events at that location, and is denoted by kde(x, y). The method implemented in GSplancs uses a quartic kernel function, whereby

kde(x, y) = ∑i ( (1 – distancei / (2 × H0) )2 ),

where the summation is over all the events in the pattern, distancei is the distance from event i to the point (x, y), and H0 specifies the kernel width. Increasing the value of H0 produces smoother density estimates.

The data required by the procedure are the coordinates of the points in the pattern (specified using the parameters `X` and `Y`) and the coordinates of a polygon within which smoothing is to be performed (specified using the parameters `XPOLYGON` and `YPOLYGON`). The kernel width must be specified using the parameter `HZERO`. The procedure calculates kernel density estimates at a grid of points spanning the specified polygon. The parameters `NX` and `NY` specify the numbers of columns and rows to be used in the grid; the default value for both parameters is 20. The output of the procedure is a matrix of kernel density estimates; any elements of the matrix which correspond to points outside the specified polygon will be returned as missing values.

The `ZGRID` parameter can save the kernel density estimates as a matrix with `NY` rows and `NX` columns, with the columns corresponding to values of the horizontal coordinate (x) arranged in ascending order, and the columns corresponding to values of the vertical coordinate (y) in ascending order. (So, for example, if these are plotted using `DSURFACE` or `DSHADE`, the `YORIENTATION` option should be left with its default setting of `reverse` to reverse the y-coordinates.)

Printed output is controlled using the `PRINT` option. The settings available are `monitoring` (which prints details about the parameter settings for the kernel smoothing process) and `grid` (which prints the grid of kernel density estimates).

Option: `PRINT`.

Parameters: `Y`, `X`, `YPOLYGON`, `XPOLYGON`, `HZERO`, `NY`, `NX`, `YGRID`, `XGRID`, `ZGRID`.

Method

A procedure `PTCHECKXY` is called to check that `X` and `Y` have identical restrictions. A similar check is made on `XPOLYGON` and `YPOLYGON`. The procedure then calls `PTCLOSEPOLYGON` to close the polygon specified by `XPOLYGON` and `YPOLYGON`. It then calls a procedure `PTPASS` to call a Fortran program to calculate edge-corrected kernel density estimates for the grid of points spanning the polygon. Finally, the `MVINSERT` function is used to replace estimates for grid points which lie outside the polygon by missing values.

Action with `RESTRICT`

If `X` and `Y` are restricted, only the subset of values specified by the restriction will be included in the calculations. `XPOLYGON` and `YPOLYGON` may also be restricted, as long as the same restrictions apply to both parameters.

References

Berman, M. & Diggle, P.J. (1989). Estimating weighted integrals of the second-order intensity of a spatial point process. Journal of the Royal Statistical Society, Series B, 51, 81-92.

Diggle, P.J. (1985). A kernel method for smoothing point process data. Applied Statistics, 34, 138-147.

Procedures: `KERNELDENSITY`, `MSEKERNEL2D`, `PTK3D`.

Commands for: Spatial statistics.

Example

```CAPTION  'PTKERNEL2D example'; STYLE=meta
VARIATE  hickx,hicky
0.069 0.014 0.049 0.057 0.094 0.015 0.106 0.036 0.130 0.126
0.081 0.079 0.027 0.068 0.027 0.069 0.034 0.081 0.066 0.132
0.040 0.115 0.031 0.108 0.040 0.074 0.041 0.074 0.039 0.156
0.023 0.207 0.098 0.142 0.084 0.176 0.053 0.221 0.035 0.300
0.036 0.310 0.050 0.284 0.027 0.327 0.108 0.307 0.134 0.328
0.143 0.353 0.128 0.379 0.105 0.411 0.129 0.385 0.036 0.358
0.030 0.360 0.028 0.354 0.031 0.376 0.030 0.453 0.068 0.453
0.075 0.490 0.047 0.474 0.023 0.486 0.069 0.481 0.076 0.422
0.082 0.458 0.089 0.444 0.107 0.437 0.146 0.444 0.089 0.473
0.078 0.470 0.084 0.513 0.110 0.516 0.132 0.518 0.122 0.539
0.124 0.555 0.124 0.563 0.103 0.537 0.091 0.555 0.118 0.554
0.027 0.539 0.079 0.562 0.025 0.605 0.026 0.587 0.030 0.571
0.039 0.594 0.047 0.582 0.054 0.580 0.077 0.594 0.070 0.635
0.054 0.617 0.042 0.589 0.069 0.567 0.081 0.620 0.092 0.575
0.102 0.571 0.147 0.569 0.131 0.618 0.098 0.620 0.120 0.608
0.081 0.671 0.102 0.676 0.116 0.680 0.118 0.683 0.094 0.701
0.079 0.648 0.065 0.671 0.047 0.701 0.053 0.709 0.035 0.701
0.030 0.692 0.026 0.684 0.047 0.666 0.064 0.694 0.032 0.711
0.024 0.727 0.027 0.741 0.035 0.725 0.040 0.732 0.045 0.721
0.070 0.712 0.045 0.760 0.032 0.772 0.080 0.721 0.078 0.725
0.092 0.732 0.097 0.720 0.136 0.763 0.127 0.773 0.106 0.747
0.131 0.752 0.109 0.772 0.145 0.787 0.095 0.804 0.129 0.807
0.142 0.844 0.135 0.843 0.100 0.794 0.010 0.795 0.027 0.787
0.028 0.799 0.029 0.814 0.064 0.838 0.009 0.819 0.027 0.877
0.038 0.866 0.037 0.882 0.054 0.851 0.066 0.867 0.070 0.903
0.068 0.912 0.063 0.910 0.035 0.900 0.034 0.899 0.024 0.907
0.001 0.864 0.054 0.865 0.061 0.863 0.077 0.867 0.085 0.855
0.116 0.882 0.120 0.886 0.136 0.863 0.142 0.881 0.127 0.899
0.115 0.905 0.101 0.921 0.137 0.911 0.123 0.893 0.101 0.923
0.123 0.925 0.136 0.978 0.127 0.939 0.115 0.942 0.114 0.950
0.108 0.965 0.105 0.959 0.104 0.975 0.081 0.974 0.078 0.952
0.026 0.939 0.035 0.942 0.071 0.931 0.076 0.953 0.065 0.981
0.064 0.981 0.047 0.749 0.041 0.960 0.031 0.965 0.031 0.963
0.052 0.949 0.207 0.918 0.183 0.908 0.172 0.908 0.175 0.880
0.216 0.892 0.219 0.853 0.160 0.864 0.198 0.852 0.278 0.912
0.245 0.912 0.229 0.896 0.240 0.889 0.246 0.896 0.274 0.890
0.219 0.945 0.244 0.947 0.279 0.979 0.288 0.924 0.234 0.943
0.209 0.922 0.168 0.922 0.163 0.932 0.170 0.763 0.163 0.767
0.154 0.767 0.159 0.756 0.157 0.723 0.179 0.748 0.166 0.724
0.281 0.780 0.258 0.768 0.229 0.815 0.238 0.816 0.249 0.829
0.248 0.835 0.279 0.804 0.265 0.802 0.225 0.792 0.228 0.789
0.153 0.831 0.162 0.846 0.167 0.812 0.176 0.815 0.174 0.831
0.203 0.839 0.211 0.827 0.160 0.784 0.186 0.845 0.155 0.607
0.193 0.568 0.174 0.598 0.166 0.610 0.268 0.592 0.258 0.590
0.260 0.582 0.253 0.703 0.276 0.677 0.289 0.672 0.207 0.700
0.156 0.670 0.162 0.680 0.148 0.661 0.161 0.489 0.209 0.495
0.224 0.477 0.228 0.487 0.222 0.457 0.220 0.445 0.238 0.550
0.247 0.519 0.229 0.522 0.221 0.521 0.254 0.498 0.262 0.524
0.159 0.555 0.212 0.527 0.158 0.527 0.201 0.521 0.193 0.325
0.216 0.325 0.286 0.408 0.289 0.409 0.223 0.402 0.229 0.400
0.211 0.395 0.212 0.255 0.184 0.288 0.198 0.062 0.183 0.0
0.148 0.015 0.185 0.013 0.251 0.066 0.256 0.013 0.271 0.016
0.258 0.019 0.234 0.012 0.242 0.126 0.242 0.136 0.268 0.108
0.265 0.088 0.253 0.104 0.256 0.071 0.398 0.154 0.416 0.167
0.424 0.156 0.413 0.182 0.370 0.251 0.419 0.273 0.385 0.273
0.290 0.293 0.394 0.307 0.404 0.312 0.415 0.306 0.417 0.326
0.372 0.368 0.302 0.008 0.320 0.061 0.294 0.066 0.406 0.008
0.289 0.095 0.339 0.131 0.409 0.408 0.404 0.418 0.335 0.407
0.354 0.422 0.310 0.438 0.332 0.426 0.317 0.465 0.338 0.477
0.394 0.436 0.417 0.450 0.427 0.436 0.430 0.447 0.474 0.477
0.329 0.532 0.330 0.531 0.335 0.508 0.353 0.561 0.323 0.613
0.348 0.620 0.347 0.667 0.409 0.649 0.356 0.709 0.304 0.701
0.331 0.718 0.307 0.716 0.323 0.737 0.331 0.727 0.333 0.746
0.342 0.725 0.347 0.727 0.358 0.725 0.360 0.769 0.342 0.771
0.344 0.761 0.346 0.755 0.302 0.752 0.304 0.769 0.318 0.781
0.333 0.763 0.387 0.722 0.425 0.719 0.370 0.775 0.405 0.847
0.419 0.819 0.408 0.833 0.398 0.832 0.390 0.839 0.367 0.830
0.304 0.785 0.308 0.792 0.314 0.802 0.328 0.787 0.329 0.847
0.312 0.654 0.321 0.865 0.325 0.882 0.323 0.902 0.294 0.909
0.380 0.856 0.389 0.927 0.425 0.973 0.384 0.972 0.366 0.973
0.307 0.985 0.291 0.986 0.412 0.946 0.465 0.897 0.463 0.915
0.440 0.987 0.461 0.987 0.497 0.958 0.438 0.756 0.553 0.760
0.576 0.833 0.475 0.834 0.436 0.841 0.513 0.703 0.538 0.522
0.459 0.486 0.490 0.489 0.498 0.471 0.501 0.435 0.501 0.446
0.444 0.435 0.578 0.501 0.543 0.470 0.556 0.465 0.540 0.452
0.448 0.542 0.459 0.537 0.491 0.522 0.475 0.522 0.459 0.527
0.492 0.561 0.456 0.530 0.438 0.350 0.473 0.332 0.473 0.308
0.556 0.354 0.437 0.421 0.446 0.412 0.508 0.410 0.482 0.403
0.487 0.182 0.439 0.157 0.534 0.254 0.569 0.127 0.495 0.119
0.439 0.104 0.459 0.094 0.693 0.006 0.686 0.008 0.708 0.133
0.657 0.128 0.577 0.105 0.608 0.098 0.619 0.132 0.609 0.126
0.631 0.168 0.621 0.201 0.620 0.203 0.617 0.190 0.708 0.184
0.671 0.218 0.619 0.347 0.659 0.354 0.694 0.376 0.682 0.377
0.601 0.385 0.585 0.404 0.616 0.491 0.615 0.492 0.636 0.496
0.639 0.492 0.682 0.442 0.712 0.458 0.706 0.476 0.696 0.466
0.672 0.476 0.658 0.494 0.714 0.501 0.661 0.525 0.673 0.534
0.660 0.562 0.629 0.516 0.617 0.537 0.604 0.543 0.588 0.547
0.584 0.595 0.609 0.597 0.712 0.584 0.703 0.618 0.667 0.702
0.666 0.715 0.579 0.718 0.641 0.739 0.602 0.753 0.695 0.737
0.686 0.751 0.672 0.762 0.656 0.721 0.659 0.795 0.598 0.839
0.619 0.841 0.584 0.855 0.629 0.910 0.585 0.854 0.654 0.851
0.654 0.897 0.661 0.937 0.683 0.948 0.680 0.987 0.677 0.923
0.663 0.958 0.627 0.952 0.639 0.935 0.640 0.983 0.640 0.983
0.623 0.986 0.608 0.979 0.596 0.989 0.639 0.983 0.767 0.922
0.733 0.902 0.747 0.883 0.779 0.873 0.839 0.913 0.813 0.960
0.848 0.981 0.852 0.979 0.854 0.984 0.858 0.944 0.721 0.978
0.782 0.974 0.776 0.947 0.728 0.924 0.737 0.718 0.838 0.782
0.811 0.769 0.821 0.752 0.831 0.744 0.855 0.844 0.823 0.812
0.820 0.805 0.828 0.813 0.827 0.811 0.819 0.813 0.815 0.819
0.758 0.819 0.768 0.831 0.742 0.648 0.789 0.620 0.793 0.585
0.771 0.597 0.763 0.583 0.748 0.604 0.831 0.650 0.803 0.637
0.842 0.635 0.816 0.591 0.804 0.588 0.798 0.706 0.803 0.700
0.806 0.701 0.811 0.665 0.801 0.680 0.832 0.674 0.744 0.703
0.786 0.711 0.750 0.671 0.769 0.495 0.738 0.471 0.756 0.472
0.764 0.470 0.777 0.443 0.753 0.442 0.748 0.453 0.738 0.446
0.731 0.439 0.802 0.465 0.848 0.479 0.823 0.438 0.804 0.545
0.827 0.544 0.830 0.538 0.842 0.555 0.831 0.509 0.741 0.537
0.782 0.550 0.774 0.510 0.727 0.526 0.841 0.338 0.803 0.413
0.816 0.395 0.746 0.407 0.790 0.393 0.725 0.422 0.784 0.389
0.727 0.201 0.773 0.185 0.832 0.149 0.802 0.155 0.854 0.268
0.832 0.222 0.829 0.223 0.825 0.233 0.846 0.256 0.778 0.279
0.789 0.253 0.729 0.231 0.782 0.014 0.794 0.032 0.823 0.015
0.785 0.078 0.748 0.123 0.950 0.021 0.926 0.052 0.943 0.093
0.951 0.080 0.907 0.115 0.895 0.149 0.908 0.148 0.976 0.181
1.000 0.199 0.991 0.199 0.970 0.211 0.944 0.205 0.972 0.264
0.923 0.278 0.916 0.277 0.997 0.234 0.880 0.227 0.898 0.254
0.866 0.293 0.881 0.289 0.906 0.305 0.896 0.340 0.892 0.343
0.883 0.325 0.874 0.330 0.893 0.315 0.913 0.310 0.929 0.315
0.968 0.285 0.932 0.324 0.924 0.333 0.948 0.341 0.942 0.364
0.949 0.359 0.962 0.370 0.998 0.421 0.987 0.292 0.963 0.323
0.951 0.325 0.946 0.325 0.964 0.424 0.951 0.399 0.881 0.394
0.916 0.396 0.922 0.380 0.927 0.399 0.892 0.417 0.885 0.425
0.872 0.406 0.872 0.427 0.908 0.430 0.921 0.501 0.908 0.479
0.877 0.465 0.972 0.444 0.977 0.445 0.953 0.496 0.977 0.534
0.950 0.557 0.890 0.515 0.939 0.511 0.918 0.544 0.905 0.621
0.897 0.607 0.924 0.591 0.955 0.663 0.969 0.657 0.945 0.692
0.968 0.607 0.982 0.604 0.978 0.628 0.966 0.697 0.882 0.662
0.890 0.665 0.890 0.661 0.889 0.652 0.890 0.647 0.927 0.654
0.946 0.660 0.932 0.701 0.903 0.712 0.902 0.688 0.885 0.696
0.902 0.697 0.895 0.747 0.926 0.775 0.930 0.763 0.905 0.760
0.894 0.774 0.895 0.781 0.896 0.782 0.889 0.749 0.892 0.762
0.952 0.736 0.960 0.722 0.973 0.722 0.996 0.736 0.950 0.760
0.950 0.747 0.938 0.748 0.936 0.771 0.969 0.737 0.953 0.791
0.957 0.805 0.959 0.800 0.996 0.802 0.972 0.837 0.974 0.827
0.944 0.826 0.883 0.789 0.874 0.794 0.919 0.792 0.916 0.828
0.908 0.854 0.900 0.841 0.881 0.855 0.868 0.857 0.921 0.884
0.923 0.921 0.934 0.856 0.963 0.904 0.936 0.922 0.968 0.902
0.984 0.931 0.998 0.975 0.987 0.977 0.992 0.986 0.963 0.985
0.944 0.977 0.930 0.277 0.957 0.939 0.994 0.985 0.883 0.958
0.909 0.963 0.925 0.989 0.879 0.985 0.896 0.961 0.891 0.991
0.858 0.984 0.391 0.402 0.421 0.383 :
VARIATE    xpoly; VALUES=!(0,1,1,0)
&          ypoly; VALUES=!(0,0,1,1)
PTKERNEL2D Y=hicky; X=hickx; YPOLYGON=ypoly; XPOLYGON=xpoly;\
HZERO=0.1; NY=25; NX=25; ZGRID=hickden
DPTMAP     [TITLE='kernel density estimate for hickories'; KEYWINDOW=0]\
Y=hicky; X=hickx
AXES       WINDOW=1; STYLE=none
DCONTOUR   [SCREEN=keep] hickden
PEN        1 ...5; BRUSH=1,9,11,13,14