[Qgis-user] Creating Geological Maps

[Alex Mandel]

On 10/16/2011 01:32 PM, Gerhardus Geldenhuis wrote:
> 
> My first question is with regards to the png images that I am using. When I
> add these images as a raster layer they appear very dirty and when zooming
> in the detail is obscured as if someone has rubbed over it. At first I
> thought that the issue was jpeg compression which took away detail so I
> resaved the images as png files and double checked using various image
> viewers under Ubuntu that the image quality is up to scratch. So for some
> reason Quantum GIS is not displaying these images correctly how do I fix
> this?
> 

Tiff is usually the best format to work with. If you can go back and
scan as tiff, make sure to do as high a dpi as you need (depending on
your needs 300-600 dpi+). You are correct JPEG will compress and ruin
your quality, converting jpeg to png will solve nothing if it's already
JPEG.

Just to check, do you have projection on-the-fly turned on? For best
image quality the image needs to be in it's native projection. Though in
this case it sounds like you just opened the image file to look at it.
How does it look in something like GIMP when you zoom in?

> Second question is how can I "align" this png file with with an actual
> co-ordinate system. I have marked 4 points on my paper maps and lines
> between these points that represent the UTM grid on which I worked and I
> would need to at least roughly align this image with the UTM grid.
> 

Georeferencing plugin, this will turn your tiff into a GeoTiff, the same
as what you might get from preprocessed ASTER data. You can mark and
enter known coordinate locations and then warp the image to fit.

> Thirdly I am not sure how to draw on a new layer but still view my image as
> a template for the digitizing.
> 
> I am more than happy to read any documentation and work through tutorials.
> What is lacking at the moment is the terminology to search for the correct
> things and experience. I am working through a number of tutorials but are
> still struggling a bit to connect A to B.
> 
Read the manual on the QGIS website, create a new vector layer and
editing it can be over anything else you have loaded in the map view.
http://qgis.org/en/documentation/manuals.html

> I will eventually add some ASTER imagery but it is my understanding that
> these are in tiff format and contains extra information like spatial
> referencing. I suspect that if I can master the above then adding ASTER
> imagery will be easy.
> 
> Lastly is there any geological map symbol databases available?
>
It's been discussed and some work has been done on it but nothing
comprehensive yet. If you have Images or Fonts of the symbols you want
you can easily convert them for use in QGIS.


> I would appreciate any pointers or brief/detailed outlines of the
> methodology I should be following to get best results.
> 
> Best Regards
> 
> 


Enjoy,
Alex