Interpolating an irregular grid

Question

I have a dataset with lat/lon and depth parameters, taken on an irregular grid. I'd like to plot an interpolated bathymetry map. I've seen several solutions for regular grids, but that just doesn't apply... Any suggestions would be appreciated.

A 50-point subset of my data:

df <- structure(list(Lat = c(49.33805, 49.33805, 49.33817, 49.33819, 
49.33823, 49.33823, 49.33827, 49.33829, 49.33834, 49.33844, 49.33846, 
49.33846, 49.33847, 49.33847, 49.33847, 49.33848, 49.33849, 49.33849, 
49.33849, 49.33856, 49.33859, 49.33861, 49.33862, 49.33865, 49.33866, 
49.33868, 49.33869, 49.33869, 49.3387, 49.33871, 49.33872, 49.33875, 
49.33877, 49.33878, 49.33882, 49.33883, 49.33883, 49.33884, 49.33884, 
49.33884, 49.33887, 49.33888, 49.33889, 49.33891, 49.33891, 49.33891, 
49.33893, 49.33893, 49.33894, 49.33895), Long = c(-117.76914, 
-117.76943, -117.76852, -117.76878, -117.76912, -117.76953, -117.76981, 
-117.76847, -117.76991, -117.76768, -117.76883, -117.76914, -117.76679, 
-117.76954, -117.76989, -117.76743, -117.76655, -117.76788, -117.76844, 
-117.77002, -117.76815, -117.76704, -117.76775, -117.76608, -117.76644, 
-117.7695, -117.76883, -117.76986, -117.76573, -117.76911, -117.76843, 
-117.76741, -117.76673, -117.77012, -117.76543, -117.76715, -117.76813, 
-117.76512, -117.76611, -117.76781, -117.76572, -117.76477, -117.76641, 
-117.76451, -117.7688, -117.76952, -117.76912, -117.76987, -117.76739, 
-117.76507), Depth = c(5.75, 5.75, 5.75, 5.75, 9.75, 5.75, 4.75, 
10.75, 3.75, 6.75, 12.75, 15.75, 4.75, 8.75, 5.75, 2.75, 5.75, 
9.75, 15.75, 2.75, 14.75, 14.75, 16.75, 5.75, 12.75, 10.75, 16.75, 
7.75, 7.75, 15.75, 16.75, 14.75, 11.75, 2.75, 5.75, 15.75, 17.75, 
5.75, 10.75, 15.75, 13.75, 3.75, 16.75, 4.75, 16.75, 12.75, 16.75, 
8.75, 16.75, 7.75), N = c(389L, 390L, 352L, 353L, 388L, 391L, 
426L, 351L, 427L, 316L, 354L, 387L, 247L, 392L, 425L, 280L, 246L, 
317L, 350L, 428L, 318L, 279L, 315L, 216L, 245L, 393L, 355L, 424L, 
215L, 386L, 349L, 281L, 248L, 429L, 187L, 278L, 319L, 186L, 217L, 
314L, 214L, 161L, 244L, 160L, 356L, 394L, 385L, 423L, 282L, 185L
), VelMagnit = c(7.84, 5.74, 5.41, 9.59, 7.02, 9.39, 13.1, 7.16, 
29.22, 2.02, 1.44, 6.88, 35.82, 8, 12.6, 37.27, 26.95, 13.3, 
3.35, 11.1, 7.48, 23.57, 18.77, 38.21, 20.69, 4.53, 7, 8.84, 
74.77, 9.49, 18.75, 8.26, 32.66, 2.77, 39.31, 22.61, 29.11, 36.88, 
33.37, 30.51, 21.39, 37.23, 16.66, 20.46, 8.66, 7.08, 19.23, 
4.16, 16.01, 25.98), VelAngle = c(109.359, 234.926, 64.855, 73.644, 
100.67, 63.435, 159.905, 331.645, 331.593, 147.095, 123.69, 57.465, 
268.24, 167.005, 178.636, 224.239, 253.179, 246.519, 17.354, 
178.968, 307.942, 253.487, 279.814, 260.661, 277.778, 223.21, 
30.964, 201.922, 260.764, 288.435, 346.112, 308.118, 277.212, 
154.359, 271.166, 231.103, 318.203, 248.025, 256.13, 271.315, 
234.898, 250.543, 248.518, 241.054, 328.696, 193.055, 324.739, 
170.311, 321.34, 248.076), North = c(5465321.35407466, 5465320.45673062, 
5465334.20185859, 5465335.84649416, 5465340.32938523, 5465340.53806541, 
5465345.46949452, 5465347.29204307, 5465353.67668219, 5465362.67550185, 
5465366.05612295, 5465366.13117831, 5465365.62894912, 5465368.30742982, 
5465368.10764226, 5465366.85006568, 5465367.60985361, 5465369.27129842, 
5465369.44129325, 5465378.49168744, 5465380.30823023, 5465381.65815607, 
5465383.53421217, 5465384.93126624, 5465386.83124086, 5465391.62499386, 
5465391.43748737, 5465392.17083906, 5465390.93768874, 5465393.93779788, 
5465395.22644872, 5465396.81815796, 5465398.99484539, 5465402.67778048, 
5465404.02489866, 5465406.43767199, 5465406.45411863, 5465405.13054023, 
5465406.62568988, 5465408.19081624, 5465409.83421333, 5465409.91360362, 
5465411.67748384, 5465413.14356129, 5465416.11549776, 5465416.75272559, 
5465418.21530199, 5465418.6115072, 5465418.87768738, 5465417.78379895
), East = c(444125.003387342, 444103.946731878, 444170.258760669, 
444151.770882767, 444126.431718875, 444097.212992858, 444076.978665012, 
444174.228007541, 444069.150472669, 444231.481904453, 444148.344059708, 
444125.684605454, 444296.448416587, 444096.50059478, 444071.375433859, 
444249.563863466, 444313.78879066, 444216.996727711, 444176.233348778, 
444061.593340175, 444197.652741389, 444278.150298904, 444227.007871585, 
444347.827629692, 444321.648646752, 444099.506214185, 444148.486188144, 
444073.2190657, 444373.88336123, 444127.863992462, 444177.120505223, 
444251.29961245, 444300.804805398, 444054.654670874, 444395.709813492, 
444270.773540085, 444199.146474186, 444418.264802441, 444346.449347451, 
444222.979333791, 444374.314694461, 444443.29084392, 444324.123924214, 
444462.496268479, 444151.098575609, 444098.352789667, 444127.224871463, 
444073.059940659, 444253.383634326, 444421.480670821), angle = c(5.945307017286, 
3.75374943543428, 0.438863040413974, 0.285466052456192, 6.09695867599179, 
0.463646715792294, 5.06311289357295, 2.06568443619789, 2.06659200740893, 
5.28668957075342, 5.6951838821827, 0.567842872136355, 3.17231044842489, 
4.93919451668135, 4.73619527138189, 3.94027277259492, 3.43517448706776, 
3.55141341525058, 1.2679118884038, 4.73040077826527, 2.4793798287981, 
3.42979887297162, 2.97030604079907, 3.30458895243354, 3.00584094436967, 
3.95823221059794, 1.03037257720737, 4.32977790176249, 3.30279126330399, 
2.81984120598464, 1.81318765331187, 2.47630804931459, 3.01571950793596, 
5.15990885388856, 3.12124211451154, 3.82047337273803, 2.30029159425097, 
3.52512875671555, 3.38366982084141, 3.11864157392607, 3.75423812762484, 
3.48118136615033, 3.51652428350322, 3.64679565887207, 2.1171541958392, 
4.48453624653683, 2.18621687434062, 4.88149393161042, 2.24554061561591, 
3.52423863879703), EEnd = c(444127.468963086, 444102.380839669, 
444171.891201757, 444154.838181978, 444128.731259986, 444100.012551216, 
444078.478954484, 444173.094500332, 444064.516846156, 444231.84769125, 
444148.743444163, 444127.618030096, 444284.514049334, 444097.10023751, 
444071.475410837, 444240.896688604, 444305.18982274, 444212.930508718, 
444176.566422062, 444061.659980224, 444195.686415001, 444270.617678339, 
444220.842763233, 444335.259781332, 444314.815430257, 444098.472355955, 
444149.686686742, 444072.118945325, 444349.283143613, 444124.862991856, 
444175.620350655, 444249.133451857, 444290.004269359, 444055.054225809, 
444382.609193401, 444264.907933091, 444192.679266209, 444406.864613959, 
444335.650346807, 444212.812012208, 444368.481430089, 444431.589557366, 
444318.956366165, 444456.528248516, 444149.598724913, 444097.819698049, 
444123.524365878, 444073.293316846, 444250.049831143, 444413.446962578
), NEnd = c(5465320.48779101, 5465319.35726437, 5465334.9681139, 
5465336.74669044, 5465339.89612933, 5465341.93784146, 5465341.36865202, 
5465349.3923619, 5465362.24389325, 5465362.11018973, 5465365.78986733, 
5465367.3645667, 5465365.26223633, 5465365.70905731, 5465363.90883235, 
5465357.94954373, 5465365.01023277, 5465367.50485919, 5465370.50712937, 
5465374.79228761, 5465381.8412898, 5465379.42503303, 5465384.60066272, 
5465382.8644171, 5465387.76460223, 5465390.52443166, 5465393.4382991, 
5465389.43723712, 5465386.93745905, 5465394.93813439, 5465401.29374106, 
5465398.51774401, 5465400.36156861, 5465401.84537415, 5465404.29154015, 
5465401.70523086, 5465413.68805938, 5465400.53035034, 5465403.95920727, 
5465408.42420823, 5465405.73422226, 5465405.77984105, 5465409.64380369, 
5465409.84278294, 5465418.58193088, 5465414.45372291, 5465423.44926401, 
5465417.24462022, 5465423.04491277, 5465414.55035932), LatEnd = c(49.3380474342345, 
49.3380349676146, 49.3381817413127, 49.3381961774213, 49.3382221137942, 
49.3382378465177, 49.3382307534342, 49.3383115871151, 49.3384172309777, 
49.3384313488661, 49.3384568417901, 49.3384690705233, 49.3384645117795, 
49.3384513844775, 49.3384328439213, 49.3383947540559, 49.3384641332503, 
49.3384781403051, 49.3385018169049, 49.3385298326984, 49.3386055088849, 
49.3385906265511, 49.3386326282497, 49.3386274634674, 49.3386696711786, 
49.3386747064999, 49.3387056057661, 49.3386625123754, 49.3386653770491, 
49.3387168224261, 49.3387786336194, 49.3387603885808, 49.3387807064111, 
49.3387725497545, 49.3388245039422, 49.3387904992063, 49.3388916724367, 
49.3387928857403, 49.3388172315733, 49.3388461694421, 49.3388361915708, 
49.3388423539545, 49.3388668368414, 49.3388811684793, 49.3389317464578, 
49.3388898732875, 49.3389731367353, 49.338912727242, 49.3389810765077, 
49.3389195855133), LonEnd = c(-117.769107642156, -117.769452798913, 
-117.768498238181, -117.768733207393, -117.769092988058, -117.769488562773, 
-117.769784874489, -117.768483695931, -117.769979980219, -117.767676786145, 
-117.768821165483, -117.769112160817, -117.766952315992, -117.769531981989, 
-117.769884434776, -117.76755165188, -117.766667694915, -117.76793792113, 
-117.768438864769, -117.770021063608, -117.768177279629, -117.767145568728, 
-117.767831407383, -117.766256298647, -117.766538384655, -117.769516575962, 
-117.768812056346, -117.769879158813, -117.766063845997, -117.769153946831, 
-117.768456198264, -117.767443953382, -117.766881652868, -117.770115783579, 
-117.765607558364, -117.767227274384, -117.768223129479, -117.765273174343, 
-117.766253868597, -117.767945278942, -117.765802218797, -117.764933584222, 
-117.766484443928, -117.764590885974, -117.768816790031, -117.769528915231, 
-117.769176368711, -117.76986689595, -117.767434770472, -117.765184527934
)), .Names = c("Lat", "Lon", "Depth", "N", "VelMagnit", "VelAngle", 
"North", "East", "angle", "EEnd", "NEnd", "LatEnd", "LonEnd"), row.names = c(NA, 
50L), class = "data.frame")

library(ggplot2)
library(ggmap)

prep <- get_googlemap(
center = c(-117.7670, 49.34027),
zoom = 17, 
maptype = 'hybrid',
scale = 2)

map <- ggmap(prep, 
    size = c(100, 200),
    extent='device', 
    darken = 0.5,
    legend = "bottom",
    base_layer = ggplot(data = df, aes(x = Lon, y = Lat))) 

map +
    geom_point(aes(fill = Depth), size = 3, shape = 21)

Sorry, but you really should try to read the [**about**](http://stackoverflow.com/about) and [**FAQ**](http://stackoverflow.com/faq) sections of the website to help you understand *how* to ask a good question. Please also read [**how to make a great reproducible example**](http://stackoverflow.com/q/5963269/1478381) for R specifically and update your question accordingly or this question will likely get closed as off-topic. — Simon O'Hanlon, Sep 12 '13 at 16:08
I've taken the gg-tags out because the interpolation is a separate process to the graphics. — Spacedman, Sep 12 '13 at 17:04
Spacedman is probably on the right track. Alternatively, you could regularize your lat&long grids via a spline fit, and then spline the bathymetry data to the new grid. — Carl Witthoft, Sep 12 '13 at 17:28

score 1 · Accepted Answer · answered Sep 12 '13 at 17:07

Read the Spatial Task View on CRAN and use one of the interpolation techniques mentioned there. In particular the automap package can do kriging and inverse distance weighting. You can get not only estimates from irregular samples onto a regular grid but error estimates too.

If you generate your output into a raster object you can use all the goodies from the raster package for visualisation and manipulation, and the rasterVis packages for visualisation.

Interpolating an irregular grid

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