<font size=3 face="Arial">Hi Gerhardus,</font><br><font size=3 face="Arial"> Just
to clarify on image file formats a little:</font><br><br><font size=3 face="Arial">JPEG - Best used with photos. You're correct
that it loses quality when compressed. This is called "lossy compression".</font><br><br><font size=3 face="Arial">PNG - Also commonly used with photos, the
compression with this is lossless, so you can set it as high as you like
and no quality will be lost.</font><br><br><br><font size=3 face="Arial">Generally speaking while good for storing
general imagery, the above two formats don't typically hold spatial information
so aren't used in a GIS.</font><br><br><font size=3 face="Arial">TIF (also TIFF) - There's about a trillion
different types of TIF file format features. This is the file type that
in the GIS world is commonly used to store raster imagery. There are others,
but this one is the most supported, even if different aspects are supported
by different applications.</font><br><font size=3 face="Arial">By default they're uncompressed, but they
can be compressed using a number of methods, LZW compression is a popular
choice and is lossless. TIFs themselves don't always store spatial information
but may come with a "world file" (tfw or tab format) which is
a small text file which contains that information. Some TIFs do store spatial
information within the TIF file itself and these are called "GeoTIFFs".</font><br><font size=3 face="Arial">Some (geo)tiffs can also store "pyramids"
- these make large rasters display faster when zoomed out.</font><br><br><font size=3 face="Arial">Hopefully that clears things up a little.</font><br><font size=3 face="Arial">Regards,</font><br><br><font size=3 face="Arial">Jonathan</font><br><br><br><br><br><font size=1 color=#5f5f5f face="sans-serif">From:
</font><font size=1 face="sans-serif">Gerhardus Geldenhuis
<gerhardus.geldenhuis@gmail.com></font><br><font size=1 color=#5f5f5f face="sans-serif">To:
</font><font size=1 face="sans-serif">tech@wildintellect.com</font><br><font size=1 color=#5f5f5f face="sans-serif">Cc:
</font><font size=1 face="sans-serif">qgis-user@lists.osgeo.org</font><br><font size=1 color=#5f5f5f face="sans-serif">Date:
</font><font size=1 face="sans-serif">16/10/2011 22:26</font><br><font size=1 color=#5f5f5f face="sans-serif">Subject:
</font><font size=1 face="sans-serif">Re: [Qgis-user]
Creating Geological Maps</font><br><font size=1 color=#5f5f5f face="sans-serif">Sent by:
</font><font size=1 face="sans-serif">qgis-user-bounces@lists.osgeo.org</font><br><hr noshade><br><br><br><font size=3>On Sun, Oct 16, 2011 at 10:03 PM, Alex Mandel <</font><a href=mailto:tech_dev@wildintellect.com><font size=3 color=blue><u>tech_dev@wildintellect.com</u></font></a><font size=3>>
wrote:</font><br><font size=3>On 10/16/2011 01:32 PM, Gerhardus Geldenhuis wrote:</font><br><font size=3>Just to check, do you have projection on-the-fly turned
on? For best<br>image quality the image needs to be in it's native projection. Though in<br>this case it sounds like you just opened the image file to look at it.<br>How does it look in something like GIMP when you zoom in?</font><br><br><font size=3>Hi Alex</font><br><font size=3>Many thanks for the reply!</font><br><br><font size=3>No idea if I have project on-the-fly turned on, I could
not see any reference to it in the project properties or options.</font><br><font size=3>Native projection? I scanned the paper images and the
scanner saved them as jpeg files. I then opened up the images in The Gimp
rotated and aligned the to a drawing grid in Gimp because they
were about 1 degree skewed. I had pencilled lines on the paper
that represented UTM grid lines. I saved these as both jpg and png
format both in lowest compression thus highest quality. Viewing either
the jpg or png file in Gimp or Image Viewer is fine and if I zoom in to
1:1 scale the quality is perfect.</font><br><font size=3> </font><br><font size=3><br>> Second question is how can I "align" this png file with
with an actual<br>> co-ordinate system. I have marked 4 points on my paper maps and lines<br>> between these points that represent the UTM grid on which I worked
and I<br>> would need to at least roughly align this image with the UTM grid.<br>><br></font><br><font size=3>Georeferencing plugin, this will turn your tiff into a
GeoTiff, the same<br>as what you might get from preprocessed ASTER data. You can mark and<br>enter known coordinate locations and then warp the image to fit.</font><br><br><font size=3>That sounds excellent I am going to try that now.</font><br><font size=3> </font><br><font size=3><br>> Thirdly I am not sure how to draw on a new layer but still view my
image as<br>> a template for the digitizing.<br>><br>> I am more than happy to read any documentation and work through tutorials.<br>> What is lacking at the moment is the terminology to search for the
correct<br>> things and experience. I am working through a number of tutorials
but are<br>> still struggling a bit to connect A to B.<br>></font><br><font size=3>Read the manual on the QGIS website, create a new vector
layer and<br>editing it can be over anything else you have loaded in the map view.</font><font size=3 color=blue><u><br></u></font><a href=http://qgis.org/en/documentation/manuals.html target=_blank><font size=3 color=blue><u>http://qgis.org/en/documentation/manuals.html</u></font></a><br><font size=3><br>> I will eventually add some ASTER imagery but it is my understanding
that<br>> these are in tiff format and contains extra information like spatial<br>> referencing. I suspect that if I can master the above then adding
ASTER<br>> imagery will be easy.<br>><br>> Lastly is there any geological map symbol databases available?<br>></font><br><font size=3>It's been discussed and some work has been done on it
but nothing<br>comprehensive yet. If you have Images or Fonts of the symbols you want<br>you can easily convert them for use in QGIS.</font><br><br><br><font size=3>A shame, I have send of an email to the British Geological
Survey and see what they come back with. I might have access to the ArcGIS
and could load the images database provided by the US Geological Survey.
Not sure if ArcGIS would allow me to export it into something more usable.
My google results turned up an email thread which suggested that there
was some work done on supporting gdb files... </font><br><font size=3> </font><br><font size=3>Regards</font><br><br><font size=3>-- <br>Gerhardus Geldenhuis</font><tt><font size=2>_______________________________________________<br>Qgis-user mailing list<br>Qgis-user@lists.osgeo.org<br></font></tt><a href="http://lists.osgeo.org/mailman/listinfo/qgis-user"><tt><font size=2>http://lists.osgeo.org/mailman/listinfo/qgis-user</font></tt></a><tt><font size=2><br></font></tt><br><BR>
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