0

Using SharpMap (Windows Forms) how can I display an overlay image over the map tile background so that the image scales and moves accordingly with the map zoom and pan? I want to implement a georeferencing like functionality.

I tried using SharpMap.Layers.GdiImageLayer but I didn't find a way to position it to a custom position (real world coordinate) - it is getting placed by default at origin [0,0] (the background tile coordinates). Is there a way to define a relation (transformation) to place it in a particular position?

I managed to get closer to a solution using VectorLayer with RasterPointSymbolizer but the symbol (image loaded for symbol) would need to be transformed on map scaling/zoom (so that corners remain in the same real world coordinates) - the math calculation behind looks a little complicated for a solution that seems more like a workaround than a natural one. As a note - I don't need precise calculation using projection/real geoid as I am doing this only at building level.

Using GDAL - GeoTIFF might be a choice here by generating a GeoTIFF based on the original image and making the georeferencing metadata dynamic based on UI controls? The original image is in raster format (JPG) with no geographic metadata.

Is there a better solution?

If VectorLayer - RasterPointSymbolizer is the best choice, do you have an example for symbol(image) synchronization with the map view?

Alex P.
  • 1,140
  • 13
  • 27

1 Answers1

1

As far as i can tell the GdiImageLayer calculates the position based on a world-file (GdiImageLayer.SetEnvelope()). Here is the link to the method. This meta file has to have the same name in the same location but the filetype must be of type *.wld. There you set the position (top left corner) and the skew in x and y axis. So rotation will be perserved. I never tried this but i would suggest correct zooming would work

(The wiki article offers also some good understanding for world files)

There might be another way if no world file is present and the information rests in the header. There is a GDalSample loading a GeoTiff Image onto an existing map. The example can be found in the WinFormSamples and the Different kind of layers supported by [MapBox] Example. The map is showing the overlay only while magnifying and not fully function but maybe a good hint

theDrifter
  • 1,631
  • 6
  • 24
  • 40