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Re: Placing images in the coordinate system?

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  • Subject: [mg103815] Re: Placing images in the coordinate system?
  • From: pfalloon <pfalloon at>
  • Date: Wed, 7 Oct 2009 07:03:20 -0400 (EDT)
  • References: <33341602.1254576310852.JavaMail.root@n11> <ha9qdu$7pb$>

On Oct 4, 8:38 pm, "David Park" <djmp... at> wrote:
> Dave,
> As usual, I would do try this with the Presentations package, but you could
> probably do it without the package with a little more work and perhaps less
> intuitively.
> I would draw everything on a "piece of paper" and not use an Axis or Frame
> as it is difficult to control the overall image dimensions with them.
> Then you would need a mapping from your {long, lat} coordinates to {x,y} on
> the piece of paper. You would have to have some map projection for the 2D
> image of the moon surface. It might be difficult to find what the projection
> was for the image you have.
> Presentations has a routine DrawingTransform that will transform any
> graphics you draw, say in the {long, lat} coordinates, to the {x,y}
> coordinates. It also has free standing scales, XTickLine and YTickLine that
> you can place on the piece of paper, say just outside the boundaries of the
> moon map. That way you get your axes. You could also use DrawingTransformon
> these so they would give {long,lat} coordinates on the {x,y} plot.
> So assuming we can either Rasterize the moon image, or use Inset, to place
> it at specific coordinates and scale on the piece of paper, the plotting
> statement would look something like this:
> Draw2D[
>  {moonimage,
>   {your graphics, XTickLine[...], YTickLine[...]}
>     /. DrawingTransform[Function[{long,lat}, xcoordinate],
>                         Function[{long,lat}, ycoo=
>   Text labels placed on the piece of paper},
> Options...]
> David Park
> djmp... at comcast.net 
> From: Dave [mailto:uber.da... at]
> Hello,
> Using Mathematica 7.0, how can I take an image and give it a position
> and scale, so that it can be combined with other graphics?
> Here's what I am trying to do: I would like to have an image map of
> the moon as the background for my plot or contour plot. I want to be
> able to plot points by their lat,lon positions and have them appear at
> the correct points on the map.
> I came up with a hack to do this by rasterizing the plot using Image[]
> so that it is the same resolution as the moon image, and then
> combining the two images.
> (I found a similar technique here:
> The problem is this does not work if the plot has Axes->True, because
> some space is used for the axes, so the coordinate systems don't match
> exactly anymore.
> I really would like to have both Axes and the image together. Is there
> a good way to do this?
> Thanks,
> Dave

What about just importing the image as a Graphics object:

img = Import["image.gif", "Graphics"];

Show[img, Frame->True]

The x,y values correspond to the pixels, so if you can work out the
transform from pixel position to latitude/longitude (e.g.
interactively hover over the graphic while holding down the "." key)
you could overlay points etc as an Epilog. Similarly, if you want to
display the actual lat/long ticks on the axes you can use the inverse
of this map.

This is still a little fiddly, but the important step of getting the
image unambiguously positioned w.r.t. the axes is handled properly so
that things won't go awry when you add axes, padding etc.


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