Spatial analysis with R package spatstat, sidebar does not show correct values

Question

I'm trying to create a map with the spatstat package of R so that the sidebar shows the values of the third (preferably) or fourth column of my data frame and that the colors are also reflective of that third (or fourth column) chosen.

My script:

x=c(6.839887, 6.671494, 6.651083, 6.655289, 6.591903, 6.653641, 6.661709, 6.671664, 6.660044, 6.624659, 6.648162, 6.536877, 6.654134, 6.674678,6.618935, 6.677705, 6.643918, 6.644119, 6.670517, 6.583619, 6.649991, 6.647649, 6.656308, 6.645772, 6.648740, 6.643103, 6.652199, 6.666641,6.633400, 6.621282, 6.635427, 6.646127, 6.630862, 6.657919, 6.671616, 6.622935, 6.648225, 6.676911, 6.640234, 6.719334, 6.653202, 6.656747,6.724692, 6.639747, 6.630575, 6.657916, 6.618957, 6.640006, 6.645280, 6.614058, 6.576136, 6.631994, 6.617391, 6.782351, 6.620072, 6.661061,6.597216, 6.648755, 6.618436, 6.659507, 6.653993, 6.663255, 6.630893, 6.656322, 6.617265, 6.649022, 6.629346, 6.595224, 6.540263, 6.623435,6.652709, 6.608565, 6.618335, 6.645100, 6.790914, 6.643620, 6.462808, 6.680115, 6.716004, 6.668781, 6.765199, 6.674251, 6.647542, 6.724564,6.724556)

y=c(17.16749, 17.16727, 17.16678, 17.16673, 17.16813, 17.16663, 17.16652, 17.16636, 17.16629, 17.16856, 17.16521, 17.16519, 17.17002, 17.16465,17.17015, 17.16407, 17.16356, 17.17122, 17.16334, 17.17152, 17.16282, 17.16278, 17.16272, 17.17257, 17.16198, 17.17279, 17.16169, 17.16161,17.16146, 17.17352, 17.17389, 17.16076, 17.17420, 17.16046, 17.15917, 17.17571, 17.15895, 17.15881, 17.15860, 17.15827, 17.15797, 17.15776,17.17761, 17.15664, 17.15622, 17.15610, 17.15571, 17.15561, 17.15527,17.15514, 17.15494, 17.15447, 17.15438, 17.18041, 17.18053, 17.15402,17.18090, 17.15384, 17.18121, 17.15355, 17.15352, 17.15349, 17.18213,17.15242, 17.15201, 17.14978, 17.18591, 17.18688, 17.18707, 17.18761,17.14712, 17.18788, 17.18794, 17.14619, 17.18868, 17.14588, 17.14511,17.14471, 17.14440, 17.14430, 17.19116, 17.19140, 17.14222, 17.14123,17.33627)

z=c(32.23228,526.46061, -1300.03539, -376.04329, 139.67322,-913.24800,  -526.46061, 354.55511, 483.48424, 161.16141, 182.64960, 419.0196, 75.20866, -225.62598, -1536.40546, -397.53148, -1106.64169,  -440.50786, 118.18504,-290.09054, -1471.94089, 440.50786,-848.78343, -1385.98814, -676.87793, -1622.35821, -1450.45271,75.20866, -1557.89365, 161.16141, 376.04329, 354.55511, -32.23228,-1171.10626,-75.20866, 547.94880, -805.80706, 870.27162, -698.36612,-32.23228, -2331.46842,  -182.64960, 75.20866, -719.85431,-1837.24009,913.24800, -1106.64169, 698.36612, 483.48424, -676.87793, -3019.09045, 891.75981, 1106.64169, 333.06692, -913.24800,333.06692, 934.73619, 354.55511, 75.20866, -891.75981, -247.11416, -1966.16922, 139.67322, -784.31887, -569.43699, -118.18504,-440.50786, 397.53148, -655.38974, 139.67322, 53.72047, -633.90155,-633.90155, 419.01967, -547.94880, 75.20866, 569.43699, 290.09054, -376.04329, 547.94880, 75.20866, -10.74409, 182.64960,-397.53148, -479.53833 )

w=c(96326.91, 96769.46, 95127.94, 95960.41, 96423.22, 95476.93, 95825.18,96615.67, 96731.03, 96442.47, 96461.73, 96673.36, 96365.44, 96095.53,94914.31, 95941.10, 95302.53, 95902.47, 96403.96, 96037.64, 94972.60,96692.58, 95535.03, 95050.29, 95689.84, 94836.56, 94992.03, 96365.44,94894.87, 96442.47, 96634.90, 96615.67, 96269.09, 95244.36, 96230.54,96788.68, 95573.74, 97076.62, 95670.50, 96269.09, 94193.69, 96134.12,96365.44, 95651.15, 94642.01, 97114.98, 95302.53, 96923.12, 96731.03,95689.84, 93567.91, 97095.80, 97287.46, 96596.43, 95476.93, 96596.43,97134.15, 96615.67, 96365.44, 95496.30, 96076.24, 94525.17, 96423.22,95593.10, 95786.52, 96191.98, 95902.47, 96654.13, 95709.18, 96423.22,96346.17, 95728.52, 95728.52, 96673.36, 95805.85, 96365.44, 96807.89,96557.96, 95960.41, 96788.68, 96365.44, 96288.37, 96461.73,95941.10, 99451.20)

shap.lo=data.frame(x,y,z,w)

library(spatstat)
shap.lo.win <- owin(range(shap.lo[,1]), range(shap.lo[,2]))
centroid.owin(shap.lo.win) ; area.owin(shap.lo.win)

shap.lo.ppp <- as.ppp(shap.lo[,c(1,2,3)], shap.lo.win) # making a ppp object

plot(density(shap.lo.ppp,0.02), col=topo.colors(25), main='', xlab='x', 
     ylab='y')

points(x, y)

the result is shown below

I would like to know why the sidebar shows different values than the ones shown in the third column of my data frame, that is, in addition to displaying no negative values, shows values much larger than those contained in the third column.

Is it possible to do this, that is, make the colors and the sidebar represent the third or fourth column of the data frame?

I thank the help of all you!

Answer 1

Let me quote directly from the help file for density.ppp:

This function is often misunderstood.

The result of density.ppp is not a spatial smoothing of the marks or weights attached to the point pattern. To perform spatial interpolation of values that were observed at the points of a point pattern, use Smooth.ppp.

The result of density.ppp is not a probability density. It is an estimate of the intensity function of the point process that generated the point pattern data. Intensity is the expected number of random points per unit area. The units of intensity are “points per unit area”. Intensity is usually a function of spatial location, and it is this function which is estimated by density.ppp. The integral of the intensity function over a spatial region gives the expected number of points falling in this region.

So try Smooth.ppp (note the upper case S), and see if you can make that produce the results you expected.