[Qgis-user] Zooming on raster maps - Identify error

[Dr. F. Patrick Graz]

Hi Radim (and list),
I have finally had the time to follow up on your suggestion, although I
don't have the capacity to rebuild QGIS. 

Using QGIS 1.6 I opened my grass raster layer and used the Info tool to
query. I then opened a grass session and zoomed in on the same point (a
pixel corner actually) and used the pixel query.

The coordinates shown in QGIS differ from those in grass by about 3m in
latitude (resolution of my data-set is 2m). However, when I tried to
compensate (moving the cursor to the coordinates that grass showed) I still
did not get the right result to my query in QGIS. 

Any ideas?

Regards,

Patrick

-----Original Message-----
From: Radim Blazek [mailto:radim.blazek at gmail.com] 
Sent: Wednesday, March 16, 2011 4:40 PM
To: fgraz at unam.na
Cc: qgis-user at lists.osgeo.org
Subject: Re: [Qgis-user] Zooming on raster maps - Identify error

Hi,
are you able to run QGIS compiled with debug support?
With debug you can see debug output on terminal like:

Debug: qgsgrass.cpp: 1072: (runModule) qgis.g.info info=query
rast=align at alignment coor=69.5627,6.49715
Debug: qgsgrass.cpp: 1130: (getInfo) value:178.000000

As you can see, QGIS runs GRASS-QGIS module qgis.g.info to query
values. Try to find if wrong coordinates are passed to qgis.g.info or
qgis.g.info gives wrong values.

If you cannot compile with debug output, try to verify if  qgis.g.info
module works correctly, you can run it as any other module in GRASS
shell.

Radim


On Wed, Mar 16, 2011 at 11:15 AM, Dr. F. Patrick Graz <fgraz at unam.na> wrote:
> Hi Folks,
> I have been using QGis (1.5 & 1.6) to view GRASS raster layers, and ran
into
> the following snag.
>
> When I zoom in to query the raster map (using Identify) I get the wrong
> pixel value. I cross-checked the results in GRASS where the value is
> correctly identified.
>
> I had rasterised a grid of lines (2x2m pixels). The pixel values running
in
> the north-south direction seem to be detected ok. The ones running
east-west
> are not. I assumed that there is some vertical off-set but I have not been
> able to detect anything consistent. I have also cross-checked with a
raster
> layer with larger pixels - and there things work fine.
>
> Any guess as to what the issue might be?
>
> Patrick
> ------------------------------------------
> Dr. F. Patrick Graz
> Snr. Researcher,
> Multidisciplinary Research Centre,
> University of Namibia
>
>
>
>
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