Re: [Qgis-user] Linking coordinates between layers

[simonc8]

Thank you, Martin. That's brilliant!

I hadn't come across Virtual Layers before, so it's opened up a whole load
of new possibilities!



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[Qgis-user] Linking coordinates between layers

[simonc8]

I have two point layers each with a single point in them. I want to draw a
line joining the points to use to measure the distance apart. I have found
various plug-ins which allow this, but is there a way I can actually link
the point coordinates to the line layer so that if I move one of the points
the line will update automatically?

Grateful for advice.



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[Qgis-user] Opening file from zip folder to processing dialog

[simonc8]

I've read how to use the QGIS Browser to add layers into the project from
within zip files, but this doesn't seem to be available with processing
dialogs.

I'm trying to merge two raster files using Raster>Miscellaneous>Merge. For
my input files it only recognises unzipped files in the folder. If I choose
the zip folders as inputs it gives and error that this is not a recognised
file type. Is there a way of taking files into processing dialogs direct
from zip folders?

Grateful for advice.



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[Qgis-user] Creating subpolygons from two shapefile layers

[simonc8]

 

The image shows two shapefiles each containing several polygons - one
shapefile is outlined in thin black lines, the other in thick pink.

I'm trying to use Geoprocessing tools to create a new shapefile which
contains a new polygon for everytime a polygon of one layer intersects one
of the other, so I want the new shapefile to contain polygons as shown in
the second image:


 

I've tried combinations of Intersect and Union and Clip but none of these
seem to produce the result I want. Very grateful if anyone can offer advice.



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Re: [Qgis-user] Showing all items in attributes table

[simonc8]

Thanks for this. The multipart to single part seemed to clean the file as
well as show that one of my polylines existed in three separate segments. So
the file now contains 8 features whether I open it in QGIS or other
programmes.

When I was digitising I wanted to use part of one line I'd already digitised
in another line, so I made a copy, cut the line and must have incorrectly
discarded the unwanted part, or inadvertently made a second copy.

If I want to combine my line which is currently in three segments into a
single feature how do I do that? Do the different segments have to have
identical end points to join properly? (At the moment there are small gaps
between the different segments.)




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[Qgis-user] Showing all items in attributes table

[simonc8]

I've digitised a shape file layer with several polylines. In the Attribute
table it shows 8 items, but in the metadata for the file it states there are
14 features. If I open the shape file in another GIS programme it comes up
with 17 polylines, some of which are duplicates of others.

I would like to clean up the file in QGIS and remove the duplicates but if I
can't get these to show up in the Attribute table I don't know how I can
select them to delete them.

Grateful for advice.



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Re: [Qgis-user] Add a new vertex to a polyline

[simonc8]

Many thanks for this - it has solved my problem.

I thought I'd tried double-clicking but maybe I wasn't close enough to the
existing line.





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[Qgis-user] Add a new vertex to a polyline

[simonc8]

I'm editing a polyline which I previously digitised. I've gone into the node
editor which allows me to move vertices around but I can't find a way to
insert a new vertex into the line. I'm sure there must be a way and it's
driving me mad!

Grateful for advice.



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Re: [Qgis-user] QGIS project with no projection

[simonc8]

Thanks for all the responses.

I've tried the various suggestions but can't get my tiff to import properly
without specifying a projection. Even following the steps suggested in Lee
Hachadoorian's post the tiff imports and appears to show the correct units
in the information bar but when I measure distances using the Measure tool
these are nothing like what they should be.

Incidentally a geotiff doesn't necessarily have any projection information -
if you have a .tif file and an accompanying .tfw file it will merely
register the image using the coordinates specified in the .tfw file with no
information about what these refer to.



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[Qgis-user] QGIS project with no projection

[simonc8]

I want to use QGIS to make measurements such as distances and angles on a
flat scaled image which I have as a georeferenced tiff. I don't want to use
any projection - just a straightforward orthogonal linear scale in metres.
QGIS seems to require that I choose a projection. What would be the best
choice for my needs? Can I make a custom projection with no ellipsoid or
datum?

If I import my geotiff and don't specify a projection QGIS assumes my units
are in degrees rather than metres, which will make measurement of distances
and angles inaccurate.

Grateful for assistance. 



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[Qgis-user] QGIS project with no projection

[simonc8]

I want to use QGIS to make measurements on a flat scaled image which I have
as a georeferenced tiff. I don't want to use any projection - just a
straightforward orthogonal linear scale in metres. QGIS seems to require
that I choose a projection. What would be the best choice for my needs? Can
I make a custom projection with no ellipsoid or datum?

Grateful for assistance.



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[Qgis-user] Degradation of imported image quality

[simonc8]

I asked this in a different thread which (very usefully) went off the topic,
so I'm starting this new thread.

I had tried importing an index map as an image into Print Composer (before
realising how much better it was to generate an Overview map.) I noticed
that the quality of the image was considerably degraded after import into
Print Composer and subsequent export into another image. The two examples
are the original image and a segment of the exported Print Composer image.
The size of the object in Print Composer is exactly 0.9 of the original
image, and this resizing seems to be the reason for the loss of quality,
because if I imported the image into Print Composer at 100% size the
degradation is much less.

Index_map_image.png
  
Index_map_via_Print_Composer.png

  

The question is - is there a way to control the quality of an image imported
into Print Composer where a degree of resizing is involved? Does QGIS have a
better resampling option?

Grateful for advice.



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Re: [Qgis-user] Importing image to Print Composer

[simonc8]

Thank you - that explains a lot.



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Re: [Qgis-user] Importing image to Print Composer

[simonc8]

That facility sounds amazing. Do you do this by setting up the style you
want, saving a preset, then changing the style and saving another preset?

Thank you



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Re: [Qgis-user] Importing image to Print Composer

[simonc8]

Thanks for pointing me towards the visibility presets - that exactly matches
what I needed.

On my system there seem only to be six presets possible - if you want to add
a new one you have to remove one first. Is there a way of increasing this
number? It doesn't seem very logical to limit the number since the space
required to store a preset can not be more than a handful of bytes..





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Re: [Qgis-user] Importing image to Print Composer

[simonc8]

Hi

Thanks for pointing me at this. I've managed to create an index map within
the same project and create the overview outline of the main map.

However, the index map has a completely different set of layers to the main
map. Is there a way of organising the layers into groups so I could quickly
turn off all the main map layers and turn on all the index map layers (and
vice versa)?

Thanks



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Re: [Qgis-user] QGIS 2.6.1 Complex polygon not displayed properly

[simonc8]

Thanks - you've suggested a solution, although I'm not sure why it works.

I imported my original shape file into SAGA, exported it as a shape file
from SAGA and when I read the SAGA export into QGIS it had all the right
areas blank. Weird!



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[Qgis-user] QGIS 2.6.1 Complex polygon not displayed properly

[simonc8]

I append two images of the same shape file which contains a single polygon
with several lakes. In SAGA it displays correctly with all the lakes as
transparent but in QGIS the larger lakes contain the colour fill. Is there
something I'm not doing correctly in QGIS, or is there an option for
changing the way it imports a polygon?

Grateful for assistance.


http://osgeo-org.1560.x6.nabble.com/file/n5184481/single_polygon_QGIS.png 

http://osgeo-org.1560.x6.nabble.com/file/n5184481/single_polygon_SAGA.png 



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Re: [Qgis-user] QGIS 2.6.1 Complex polygon not displayed properly

[simonc8]

The polygon (there is only one polygon) was created in Golden Software Didger
from contours exported as a dxf file. I imported the shapefile into QGIS
using Add Vector Layer.

The attached image shows how the list of coordinates plot in Excel - it
shows how the coordinates trace round the main shape then go round each of
the inliers (what I am calling lakes) in the opposite direction always
returning to the common point which is the most southerly in the file.

I am confused because QGIS is obviously recognising some of these inliers as
being outside the polygon (it puts no colour in them) but others are not
being recognised.

http://osgeo-org.1560.x6.nabble.com/file/n5184487/single_polygon_Excel.png 



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