Here's another fun way of mapping airspace:  You can get sectional
charts in the form of .tif files from:

You can then read them into QGIS ... and then overlay them with
whatever other information you want, perhaps from apt.dat and
nav.dat and/or elsewhere.

  (Reading the same .tif file into GRASS doesn't work.  GRASS
  tries and fails, with no error or warning messages.  The
  resulting map has no pixels at all, according to d.histogram.
  So this is another reason to use QGIS.)

On 09/21/2011 06:10 PM, J. Holden wrote:

> Admittedly I work with GRASS solely on the text-based side - rarely
> if ever touching the GUI 

Roger that.  I, too, rely almost exclusively on the command-line
interface to GRASS.  I occasionally use the GUI to give me hints
about what CLI commands I need to use.  The stuff I need to do 
involves so many GRASS commands that I could not possibly remember
them all, let alone do them reliably, so I use a script.

> I hope I didn't misinterpret what you're writing, and hopefully that
> was of some help.

You definitely understood the questions (even though I now
realize the questions were not entirely clear) ... and you
have been very helpful.

> 3. You CAN do raster reprojection on the fly. However, your results
> won't be anywhere near as "clean" as a vector reprojection as a
> result of the different format type. Also, there are some rules - I
> believe the projection has to be in the current region of the
> location you're reprojecting to, and also the resolution must be
> sufficient in order to handle the map.

Well, YMMV but I can't get the instance I'm running to do raster 
reprojection.  It tries and fails.  I have an example where there 
are two rasters in the same location, with slightly different 
projections, plus some vector data.  If I switch projections in 
my "project" workspace, one raster or the other goes to all-white. 
The "zoom to layer" button zooms to the right place, but the image
is still all-white.  The vector data stays where it belongs, so 
that is working.

This is a low priority for me, because I am content to 
reproject all rasters to a common SRS using gdalwarp.  That
does everything I need it to do.

> 1) it's probably easiest to continue to use d.his and
> then display the resulting map using the GRASS plugin - QGIS doesn't
> really have many (if any?) raster tools, while GRASS was created
> primarily to deal with raster features (and added vectors later).

That sounds good, but I haven't figured out how to get a map
/out/ of d.his.  I think of d.his as a display function, not 
a map-calculation function.  I don't know how to find the
"resulting map" produced by d.his, not in any useful form

And here is a possibly-related question:  what colormap are
the Sectional Aeronautical Charts using, and how do I specify
it?  They show up in QGIS in beautiful natural color.  In 
particular, in QGIS, if I change the colormap on one of those 
charts, there does not appear to be any way to change it back
to the beautiful original colormap.  I assume there is some
clever colormap that the QGIS backend knows about but the GUI
does not.

I mention this because I reckon I could solve several
interesting problems by using this colormap, using r.mapcalc
if necessary to format the pixels.  This includes the "drape"
operation, which produces very nice-looking results by taking
the hue from one layer and the intensity from another.

Or maybe somebody can write a r.calc.drape module.

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