Re: Placing images in the coordinate system?

*To*: mathgroup at smc.vnet.net*Subject*: [mg103952] Re: Placing images in the coordinate system?*From*: Dave <uber.daveb at gmail.com>*Date*: Tue, 13 Oct 2009 23:20:25 -0400 (EDT)*References*: <33341602.1254576310852.JavaMail.root@n11> <ha9qdu$7pb$1@smc.vnet.net>

On Oct 7, 4:04 am, pfalloon <pfall... at gmail.com> wrote: > On Oct 4, 8:38 pm, "David Park" <djmp... at comcast.net> 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}, ycoordinate]], > > Text labels placed on the piece of paper}, > > Options...] > > > David Park > > djmp... at comcast.nethttp://home.comcast.net/~djmpark/ > > > From: Dave [mailto:uber.da... at gmail.com] > > > 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 twoimages. > > (I found a similar technique here:http://mathgis.blogspot.com/2007/12/fun-with-image-overlay.html) > > > 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. > > Cheers, > Peter. Thanks for your replies everyone! In the end, I went with the following solution suggested by Maxim: Transform the Image into a "Raster", which allows specifying a coordinate rectangle: image = Import["D:/images/pictures/moon.jpg"]; raster = Raster[Reverse@ImageData[image], {{-180, -90}, {180, 90}}]; ContourPlot[..., Prolog->raster] Cheers, Dave