After much effort, I obtained an old set of 1928-1930 USGS topo maps of Oʻahu
Island, Hawaiʻi - for a project I am working on. The maps are without collars
and used by a local archaeological firm. The geotiff maps at first showed as
completely black on my Mac system (10.10.5 - Yosemite). However I found this
link with a resultuion for the issue:
http://stackoverflow.com/questions/13925995/options-to-convert-16-bit-image
<http://stackoverflow.com/questions/13925995/options-to-convert-16-bit-image>
I opened the 16 quads for Oʻahu in Photoshop and applied auto levels, after
which they became discernable quad maps. However, when imported into QGIS, they
are now invisible. I wonder if it is possible that I stripped away the geotiff
CRS information. Prior to the Photoshop operation, the maps did appear
correctly referenced to Oʻahu Island (although they were totally opaque /
black).
Now, the maps in QGIS are not visible, although the geotiffs are several
megabytes in size and are visible when opened in Photoshop, Preview, or
whatever image viewer.
I should mention that I have successfully imported other sets of USGS maps of
Oʻahu for this project - the 1902 series, the 1916 series, the 1935 series - as
well as the current series. The early maps used the Old Hawaiian CRS (EPSG
3564) but more modern maps use WGS83, Zone 4N (EPSG 3711). I have on the fly
projection enabled and have tried many CRS settings for the maps, but nothing
results in a visible quad appearing.
Suggestions very welcome ...
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