DRG is not a separate format but is a series of  USGS Digital Raster Graphics files in .tif format.  The DRG series of files from USGS provide images of scanned paper maps in TIF format, usually along with metadata, in a form that captures the coordinate system.  Images will be imported from DRG .tif files with the correct coordinate system automatically assigned.




To import from DRG .TIF format:


  1. Choose File-Import from the main menu.

  2. In the Import dialog browse to the folder containing data of interest.

  3. Double-click the file ending in .tif for the data of interest.

  4. A table and an image will be created.





We can double-click on images that are created to view them.   For a more interesting display, we first create a new data source using a Bing street maps image server as shown in the Example: An Imageserver Tutorial topic.   We then create a map and drag and drop the Bing layer into the map, and then we drag and drop the image into the map.




The image appears using the correct projection:  it is an image of a scanned sheet of paper, complete with blank white margins.   




Zooming into the display we see every part of the paper map has been scanned.  The white paper margin blocks a view of the background Bing streets layer.


A quick hack to get rid of the white paper margin is to replace the white color in the image with transparent color.  We can do that by using the Style panel in the Contents pane to edit the palette colors used by the image.  The use of transparent color finstead of white  is a quick and dirty hack, to get rid of the collar.




We launch the Style panel and in the second interval we change the white color to transparent color.  




All parts of the image previously rendered in white color now use transparent color, so the Bing layer below can be seen.  This shows that the scanned image of the paper chart has been perfectly georegistered, with features in the image layer showing the chart lining up with features shown by the Bing layer.




Zooming out we can see the entire chart is well georegistered.




To see what projection the image layer uses, we can switch to the Component panel of the Contents pane.   That shows that our map uses Pseudo Mercator projection, while the chart image layer uses NAD27 / UTM zone 15N (EPSG:26715) coordinate system.    Manifold is reprojecting the image layer on the fly to display it for us as a layer in the map's projection, Pseudo-Mercator.

See Also









Example: Spectacular Images and Data from Web Servers


Example: An Imageserver Tutorial