overlaying specific points on an imported image

I use the imread command to import a .jpg image which has some data shown (suppose it is a part of a global map with locations of fires shown). Now I have to overlay another data set which are based on longitude and latitudes (suppose a scatter plot). How can do that?

Answer 1

[Walter Roberson]

img = imread('peppers.png');
image(img);   %display image
hold on
scatter([23; 118; 209], [74; 88; 133], 'r*');   %overlay some points
hold off

[Thishan Dharshana Karandana Gamalathge]

Thanks. Once the 4th line is corrected as scatter([23; 118; 209], [74; 88; 133], 'r*'); it is accepted. i.e. I removed the semicolon and put a comma.

[Thishan Dharshana Karandana Gamalathge]

That works to import an image. But the axes are shown in number of pixels. When I try to put actual coordinates with xlim, figure disappear as the real coordinates are much larger than the number of pixels. Also, the y-axis scale here increases from top to bottom. But in a map, latitudes increases from bottom to up.

[Walter Roberson]

set(gca, 'ydir', 'reverse')

If the real coordinates are much greater than the number of pixels, then you have two possibilities:

1. That the real coordinates should be (mostly) out of view; or
2. that when you put the image up that you should be telling MATLAB what coordinates to place the image at.

%image(long, lat, data)
image([5526201.28 5526235.05], [627267.83 625738.97], img)

Note: the coordinates you give are of the centers of the pixels of the corners.

If you have the Mapping toolbox you should consider using geoshow() and scatterm()

[Thishan Dharshana Karandana Gamalathge]

set(gca, 'ydir', 'reverse') doesn't work on the figure. I even tried set(gsa,'ylim',[33 35]). But still the figure axis shows 35 at the bottom while 33 on the top. X scale is correct and the figure appears correct.

[Walter Roberson]

image() normally sets ydir to reverse so that the lower values are at the top. Try

image(long, lat, flipud(data))
set(gca, 'ydir', 'normal')

and also try

image(long, fliplr(lat), data)
set(gca, 'ydir', 'normal')

[Abhilash]

While I am trying to plot a 2D surf() plot on a image, some of the data is not showing up on the map. Can someone help?

It comes up like this...

but the surf plot is supposed to be like this...

Thanks, Abhilash

[Walter Roberson]

please show your code for creating the underlay and the surf and any xlim ylim or alpha data manipulation