Drawing Tidal Ellipses on an m_map in MATLAB

I want to draw tidal ellipses on an m_map, but the figure is not displaying correctly. Please help me.

% 사용자 지정 위도 및 경도 (덕적도)
latitude = 37 + 13/60 + 35/3600;  % N 37° 13' 35"
longitude = 126 + 9/60 + 24/3600; % E 126° 09' 24"

% 데이터 파일 로드
fnm = 'cmems_mod_glo_phy_my_0.083deg_P1D-m_1731894708544.nc';
lon = ncread(fnm, 'longitude'); 
lat = ncread(fnm, 'latitude');
time = ncread(fnm, 'time'); 
dateT = datetime(1970, 01, 01, 00, 00, 00) + seconds(time);
u = ncread(fnm, 'uo'); 
v = ncread(fnm, 'vo'); 

% 지정된 위치에 가장 가까운 격자 점 찾기
[~, lat_idx] = min(abs(lat - latitude));
[~, lon_idx] = min(abs(lon - longitude));

% 해당 지점의 유속 데이터 추출
u_series = squeeze(u(lon_idx, lat_idx, :));
v_series = squeeze(v(lon_idx, lat_idx, :));

% 조석 성분 분석 (t_tide)
[NAME, FREQ, TIDECON, ~] = t_tide(u_series + 1i * v_series, ...
    'interval', 1, 'start time', datenum(dateT(1)), 'latitude', latitude);

% 주요 조석 성분 설정
major_constituents = {'M2', 'S2', 'K1', 'O1'};
colors = {'r', 'g', 'b', 'k'}; % 각각 빨강, 초록, 파랑, 검정
NAME = strtrim(string(NAME)); % 조석 성분 이름 정리

% 지도 설정 (m_map)
figure;
m_proj('mercator', 'lon', [120 128], 'lat', [33 40]); % 범위 설정 (한반도)
m_gshhs_l('patch', [0.8 0.8 0.8]); % 육지 표시
m_grid('box', 'fancy', 'tickdir', 'out'); % 격자 추가
hold on;

% 주요 조석 성분별로 타원 그리기
for i = 1:length(major_constituents)
    % 해당 조석 성분의 인덱스 찾기
    idx = find(strcmp(NAME, major_constituents{i}));
    if ~isempty(idx)
        % 타원 매개변수 추출
        major_axis = TIDECON(idx, 1); % 장축 반경 (확대)
        minor_axis = TIDECON(idx, 3); % 단축 반경 (확대)
        inclination = TIDECON(idx, 5) * pi / 180; % 경사각 (라디안)
        x0 = longitude; % 타원의 중심 경도
        y0 = latitude;  % 타원의 중심 위도

        % 타원 그리기
        ellipsedraw(major_axis, minor_axis, x0, y0, inclination, colors{i});
    end
end

% 제목 및 기타 설정
title('Tidal Ellipses for Major Constituents');
hold off;

[Angelo Yeo]

Can you share your data and all other necessary functions? It is a good idea to let others reproduce your issue if you want to get helped.

[은진]

I would like to share my data, but I can't due to the file size limit.

Answer 1

[Angelo Yeo]

I made some slight changes of your code and made it run in the MATLAB Answers environment. I used the drawEllipse function created by @William Rose for ellipse plotting from one of your previous questions (link).

Note that the original dataset is from Copernicus (link) and deals with ocean current not tidal current. I consulted someone around me who is researching tidal currents, and he mentioned that tidal currents are sub-concept to ocean currents. However, due to the nature of the Copernicus dataset, which provides global satellite data, the resolution may be too low to be suitable for analyzing tidal characteristics at specific locations (in this case, Deokjeokdo). If you are looking to analyze tidal characteristics at specific locations within the country (in this case, South Korea), it might be better to utilize observational data from location-specific stations provided by Korea Hydrographic and Oceanographic Agency. (link).

unzip("t_tide_v1_5.zip");

% 사용자 지정 위도 및 경도 (덕적도)
latitude = 37 + 13/60 + 35/3600;  % N 37° 13' 35"
longitude = 126 + 9/60 + 24/3600; % E 126° 09' 24"

% 데이터 파일 로드
% fnm = 'cmems_mod_glo_phy_my_0.083deg_P1D-m_1731894708544.nc';
% finfo = ncinfo(fnm)
% lon = ncread(fnm, 'longitude'); 
% lat = ncread(fnm, 'latitude');
% time = ncread(fnm, 'time'); 
% u = ncread(fnm, 'uo'); 
% v = ncread(fnm, 'vo'); 
load("oceanCurrentDataset.mat") % only using the essential data
dateT = datetime(1970, 01, 01, 00, 00, 00) + seconds(time);

% 지정된 위치에 가장 가까운 격자 점 찾기
[~, lat_idx] = min(abs(lat - latitude));
[~, lon_idx] = min(abs(lon - longitude));

% 해당 지점의 유속 데이터 추출
% u_series = squeeze(u(lon_idx, lat_idx, :));
% v_series = squeeze(v(lon_idx, lat_idx, :));

% 조석 성분 분석 (t_tide)
[NAME, FREQ, TIDECON, ~] = t_tide(u_series + 1i * v_series, ...
    'interval', 1, 'start time', datenum(dateT(1)), 'latitude', latitude);

   number of standard constituents used: 35
   Points used: 2007 of 2008
   percent of X var residual after lsqfit/var original: 79.63 %
   percent of Y var residual after lsqfit/var original: 68.41 %
   Greenwich phase computed with nodal corrections applied to amplitude 
 and phase relative to center time
   Using nonlinear bootstrapped error estimates
   Generating prediction with nodal corrections, SNR is 2.000000
   percent of X var residual after synthesis/var original: 83.96 %
   percent of Y var residual after synthesis/var original: 73.36 %
-----------------------------------
date: 29-Nov-2024
nobs = 2008,  ngood = 2007,  record length (days) = 83.67
start time: 01-Jan-2016
rayleigh criterion = 1.0
Greenwich phase computed with nodal corrections applied to amplitude \n and phase relative to center time

x0= 0.00247, x trend= 0

var(x)= 0.0034369   var(xp)= 0.0005363   var(xres)= 0.0028857
percent var predicted/var original= 15.6 %

y0= -0.00903, x trend= 0

var(y)= 0.0073277    var(yp)= 0.0019106  var(yres)= 0.0053755
percent var predicted/var original= 26.1 %

ellipse parameters with 95%% CI estimates

tide   freq      major  emaj    minor   emin     inc    einc     pha    epha      snr
 MM   0.0015122  0.011   0.014  -0.000   0.01   127.74  96.97   256.32 104.17   0.68
*MSF  0.0028219  0.066   0.020   0.007   0.02   116.79  14.35     7.80  16.83     11
 ALP1 0.0343966  0.007   0.008   0.001   0.01   127.12  75.62   251.22  90.03   0.77
 2Q1  0.0357064  0.008   0.008   0.000   0.01   118.74  64.86   256.57  76.79   0.97
 Q1   0.0372185  0.007   0.008  -0.003   0.01   126.27  74.12    95.42  95.64   0.82
 O1   0.0387307  0.004   0.007   0.001   0.01   156.03 116.35   197.71 160.44   0.24
 NO1  0.0402686  0.010   0.008  -0.000   0.01   101.89  39.95   186.81  49.61    1.5
*K1   0.0417807  0.015   0.009  -0.001   0.01   122.93  33.54   100.36  39.60    2.5
 J1   0.0432929  0.008   0.008  -0.001   0.01   127.52  68.92   116.68  62.48      1
 OO1  0.0448308  0.008   0.010  -0.001   0.01   123.83  81.44   127.67 110.83   0.61
 UPS1 0.0463430  0.013   0.013  -0.003   0.01   113.89  53.97   318.94  81.77      1
 EPS2 0.0761773  0.002   0.004  -0.001   0.00    37.07 124.59   327.74 157.17   0.18
 MU2  0.0776895  0.002   0.004   0.000   0.00    42.53 123.21    44.47 135.94   0.31
 N2   0.0789992  0.004   0.004  -0.002   0.00   154.60  93.93   265.25 104.17   0.85
*M2   0.0805114  0.012   0.005  -0.000   0.01   132.40  28.07   243.66  29.15      5
 L2   0.0820236  0.006   0.006  -0.000   0.01   143.30  63.04   267.14  64.59    1.2
 S2   0.0833333  0.001   0.004   0.000   0.00    20.72 115.08   184.30 188.47  0.077
 ETA2 0.0850736  0.010   0.008  -0.000   0.01    88.54  65.10    96.75  59.67    1.5
 MO3  0.1192421  0.006   0.007   0.002   0.01   117.59  72.62    70.67  97.33   0.82
 M3   0.1207671  0.007   0.006  -0.003   0.00   121.48  53.73    35.38  64.43    1.5
 MK3  0.1222921  0.004   0.005  -0.002   0.00   139.68  96.17   223.67 108.49   0.71
 SK3  0.1251141  0.009   0.007  -0.001   0.01   107.23  43.68    16.08  58.70    1.4
 MN4  0.1595106  0.005   0.004   0.002   0.00   121.21  69.83    53.80  73.05    1.4
 M4   0.1610228  0.004   0.005   0.001   0.00   100.42  66.43    27.73  90.60   0.83
 SN4  0.1623326  0.007   0.005   0.001   0.00   128.36  43.47   301.88  44.34    1.9
 MS4  0.1638447  0.005   0.004   0.001   0.00   122.15  73.95   212.32  79.26    1.1
 S4   0.1666667  0.006   0.005   0.002   0.00   118.89  65.27   269.25  78.07    1.1
 2MK5 0.2028035  0.005   0.005   0.001   0.01   144.05  69.22   326.80  76.59      1
 2SK5 0.2084474  0.006   0.006  -0.001   0.01    88.05  59.21   345.88  79.44      1
*2MN6 0.2400221  0.006   0.004  -0.001   0.00   114.42  37.67    50.48  45.31      2
 M6   0.2415342  0.004   0.004  -0.000   0.00   110.23  48.61    14.15  61.02    1.3
 2MS6 0.2443561  0.002   0.004   0.001   0.00   108.82  82.96   255.82 116.75   0.37
 2SM6 0.2471781  0.003   0.003   0.000   0.00   128.85  79.97   355.41  90.52   0.94
 3MK7 0.2833149  0.002   0.003   0.000   0.00   109.26  76.80    13.06 121.27   0.47
 M8   0.3220456  0.002   0.002   0.001   0.00   111.42  65.61   213.81  84.10    1.1

total var= 0.010765   pred var= 0.0024469
percent total var predicted/var original= 22.7 %

% 주요 조석 성분 설정
major_constituents = {'M2', 'S2', 'K1', 'O1'};
colors = {'r', 'g', 'b', 'k'}; % 각각 빨강, 초록, 파랑, 검정
NAME = strtrim(string(NAME)); % 조석 성분 이름 정리

% 지도 설정 (m_map)
% figure;
% m_proj('mercator', 'lon', [120 128], 'lat', [33 40]); % 범위 설정 (한반도)
% m_gshhs_l('patch', [0.8 0.8 0.8]); % 육지 표시
% m_grid('box', 'fancy', 'tickdir', 'out'); % 격자 추가
% hold on;

% 주요 조석 성분별로 타원 그리기
for i = 1:length(major_constituents)
    % 해당 조석 성분의 인덱스 찾기
    idx = find(strcmp(NAME, major_constituents{i}));
    if ~isempty(idx)
        % 타원 매개변수 추출
        major_axis = TIDECON(idx, 1); % 장축 반경 (확대)
        minor_axis = TIDECON(idx, 3); % 단축 반경 (확대)
        inclination = TIDECON(idx, 5) * pi / 180; % 경사각 (라디안)
        x0 = longitude; % 타원의 중심 경도
        y0 = latitude;  % 타원의 중심 위도

        % 타원 그리기
        drawEllipse(major_axis, minor_axis, x0, y0, inclination, colors{i});
        hold on;
    end
end

% 제목 및 기타 설정
title('Tidal Ellipses for Major Constituents');
hold off;

[은진]

Thank you so much!!!!

[Angelo Yeo]

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