[Qgis-user] QGIS-Merge or creat virtual raster files without losing definition?

[Michael Bracken]

I am new to QGIS and relatively new to GIS (so please be aware I am not that familiar with jargon).

I am trying to merge several tiff files as either a virtual raster or a simple merge. Whichever way I try the resulting display appears to lose definition (even just a couple of the files).

I have tried to set the options to no compression (merge rasters), and resolution set at highest for creating virtual raster, but street names and place names still become too pixillated to read properly.

This does not happen if I load all the files I wish to merge individually, but obviously I would rather work with the merged or virtual files.

I am using QGIS 2.2.0 on a 2.5 GHz Intel Core i5 Mac, OSX 10.9.3.

Would appreciate some help, please.

Mick

[Jonathan Moules]

Hi Mick,
QGIS is using a tool called GDALMerge to do the merging.

An alternative is to do it yourself in GDAL at the command line. It's
fairly simple.
Use the "OSGeo4W Shell" link that comes with QGIS.

Navigate to the directory that has the tif files in.
To merge all your tiffs together into a basic VRT you only need two lines:

*dir /b /s "C:\my data\lots of tiffs\*.tif" > "**C:\my data\lots of tiffs*
*\tiff_list.txt"*

That line (assuming it's windows; there's a Linux equivalent) basically
creates a list of all the tif files.
Then:

*gdalbuildvrt -input_file_list "C:\my data\lots of
tiffs\tiff_list.txt" "C:\my data\lots of tiffs\my_merged_data.vrt"*

That line turns it into a VRT file.

Cheers,
Jonathan

Post by Michael Bracken
I am new to QGIS and relatively new to GIS (so please be aware I am not
that familiar with jargon).
I am trying to merge several tiff files as either a virtual raster or a
simple merge. Whichever way I try the resulting display appears to lose
definition (even just a couple of the files).
I have tried to set the options to no compression (merge rasters), and
resolution set at highest for creating virtual raster, but street names and
place names still become too pixillated to read properly.
This does not happen if I load all the files I wish to merge individually,
but obviously I would rather work with the merged or virtual files.
I am using QGIS 2.2.0 on a 2.5 GHz Intel Core i5 Mac, OSX 10.9.3.
Would appreciate some help, please.
Mick
_______________________________________________
Qgis-user mailing list
Qgis-user at lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/qgis-user

--
This transmission is intended for the named addressee(s) only and may
contain confidential, sensitive or personal information and should be
handled accordingly. Unless you are the named addressee (or authorised to
receive it for the addressee) you may not copy or use it, or disclose it to
anyone else. If you have received this transmission in error please notify
the sender immediately. All email traffic sent to or from us, including
without limitation all GCSX traffic, may be subject to recording and/or
monitoring in accordance with relevant legislation.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20140626/bb05041f/attachment.html>