How do I find the x/y coordinates that correspond to a given latitude and longitude for my plot?

Hi I am plotting a netCDF file and an trying to plot a rectangle over an area of interest within the netCDF plot. I have tried using plot() and inputing x/y coordinates but it isn't as accurate as I want because I only have the longitude and latitude. If I input the longitude and latitude, the rectangle does not appear. I have also tried m_line() and used the latitude/longitude coordinates but that also doesn't appear in my plot.

Here is my code:

file = 'NetCDF Files/2013/snapshot-2013-04-15T00_00_00Z.nc';
ncdisp(file);
lon = ncread(file, 'lon');
lat = ncread(file, 'lat');
band1 = uint8(ncread(file, 'Band1'));
band2 = uint8(ncread(file, 'Band2'));
band3 = uint8(ncread(file, 'Band3'));
close all
figure('pos', [200, 50, 1100, 700])
minlon = -66.3;
maxlon = -65.4;
minlat = 65.6;
maxlat = 66.4;
m_proj('mercator', 'lon', [minlon maxlon], 'lat', [minlat maxlat]); hold on
m_pcolor(lon, lat, band2'); shading flat;

%m_gshhs_f('save','gshhs_f_Pang')
m_usercoast('gshhs_f_Pang','patch',[0.820,0.703,0.547]);
m_grid('box','fancy','tickdir','in')
colorbar

%this is what I was messing with but it doesn't give me the accuracy I need
%plot([-0.0035 -0.0003 -0.0003 -0.0035 -0.0035], [1.5515 1.5515 1.5536 1.5536 1.5515],'-r')

%this doesn't show up on the map
bndry_lon = [66 66.15 66.15 66 66];
bndry_lat = [-66.1 -66.1 -65.89 -65.89 -66.1];
m_line(bndry_lon, bndry_lat, 'linewi', 1, 'color', 'r');

[Kautuk Raj]

Please share the file 'NetCDF Files/2013/snapshot-2013-04-15T00_00_00Z.nc' for us to reproduce the issue.

[Noah]

I have edited the post to include a zip folder with the tiff file as well as the coastline file. Thanks.

[Mrutyunjaya Hiremath]

The issue with your code is that you are mixing up the longitude and latitude coordinates while plotting the rectangle using m_line. The correct order should be [longitude, latitude], but you have used [latitude, longitude] instead.

[华纳公司注册网址hn6660.com]

I am not able to figure out the error here.

I have been struggling with this from months. I sincerely appreciate any sort of help/guidance on this

Answer 1

[Raj]

Hello Noah,

I understand you essentially want to find x and y coordinates that correspond to a given latitude and longitude. To do so you can use the MATLAB function ‘projfwd’ provided in the Mapping Toolbox in MATLAB

Here is a sample code. You can replace the latitude and longitude with the ‘lat’ and ‘lon’ values you receive from ‘ncread’ function and adapt accordingly

% Define the latitude and longitude coordinates
latitude = 40.7128;   
longitude = -74.0060; 

%Create a map projection object
projection = defaultm('mercator');  % Example projection (Mercator)

% Convert latitude and longitude to x/y coordinates
[x, y] = projfwd(projection, latitude, longitude)

With the x and y coordinates, you can proceed to draw a rectangle over the required area within the plot

Additionally refer to the documentation of the respective functions for better understanding-

• ‘defaultm’- https://www.mathworks.com/help/map/ref/defaultm.html
• ‘projfwd’- https://www.mathworks.com/help/map/ref/projcrs.projfwd.html

I hope this resolves your query and you are able to proceed further!