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Hi Devs,<br>
Gavin & I have swapped a few emails discussing this, and would
like to get a wider opinion as to whether it is a QGIS error, or
not.<br>
QGIS version in use by me, as per attached screenshot.<br>
<br>
<b>The problem:</b><br>
<blockquote>If I read in a CSV layer that uses South Oriented CRS,
then QGIS displays this layer "mirrored" even after telling QGIS
what the applicable layer CRS is.<br>
Furthermore, when I move the mouse downwards or to the left, the
coordinate readout values decreases instead of increases.<br>
In short, if I work in a South Oriented CRS, I must deal with an
inverted picture or an incorrect coord readout.<br>
Is this correct behaviour for QGIS?<br>
</blockquote>
<b><u><big>To test:</big></u></b><br>
<b><br>
Fixed test parameters:</b><br>
<ul>
<li>Always start with a "new" QGIS so that only default project
settings are "set". (EPSG:4326 but 'on the fly CRS' off)<br>
</li>
<li>Only load the CSV file so that there are no other map layers
to to contend (CRS wise) with.</li>
<li>The absolute position (on earth) of the test data is not
important - we are looking to see that QGIS displays the points
correctly<u> relative to each other</u>, and that the coordinate
readout is correctly increasing South and Westwards.<br>
</li>
<li>Use only the two following CRS (note the only difference is
the axis parameter)<br>
<b>EPSG:2048</b> is +proj=tmerc +lat_0=0 +lon_0=19 +k=1
+x_0=0 +y_0=0 <b>+axis=wsu</b> +ellps=WGS84
+towgs84=0,0,0,0,0,0,0 +units=m +no_defs<br>
<b>USER:100004</b> is +proj=tmerc +lat_0=0 +lon_0=19 +k=1 +x_0=0
+y_0=0 <b>+axis=enu</b> +ellps=WGS84 +towgs84=0,0,0,0,0,0,0
+units=m +no_defs<br>
</li>
<ul>
<li><b>Testdata:</b> <br>
The coords below should be EPSG:2053 - in other words, the
South Africa Land Survey coord system, which is essentially a
distance from the central meridian (19E in this case) and a
distance from the Equator (some 3769Km in this case). Note
that the further South you go, the larger the '3769xxx' value
gets (ie: South facing)<br>
<blockquote>A,19961.49,3769105.30<br>
B,19902.64,3769135.18<br>
C,19899.91,3769132.99<br>
L,20095.87,3769783.70</blockquote>
The relative positions of these 4 values ("in real life")
are: A at the top, B and C Eastish of A (but B below [South]
of C) and L far below A and slightly to the West of A (see
attached 'correct_orientation.jpg')</li>
</ul>
</ul>
<b>Test results:</b><br>
<ul>
<li>Open QGIS, add delimited text layer and specify its CRS to be
EPSG:2048, keep Project CRS on the fly "off".<br>
Result:<br>
<blockquote>Image is inverted (A is South of L) and B & C
are West of A. <br>
Coordinate values are both +ve numbers and mouse position
coords decrease to West and South<br>
</blockquote>
</li>
<li>Using above data, Set Project CRS (on the fly = YES) to same
EPSG:2048<br>
Result:<br>
<blockquote>No change from above.<br>
</blockquote>
</li>
<li>Simply change Project CRS to EPSG:100004 as defined earlier in
this email.<br>
Result:<br>
<blockquote>Image orientation is now correct BUT<br>
Mouse coords readout shows -ve coord values, and these values
still (numerically) DECREASE towards the West and South.<br>
</blockquote>
</li>
</ul>
<b>Start with a "new" QGIS</b> (to pedantically make certain that no
CRS functionality is left over from above tests)<br>
<ul>
<li>Open QGIS, add <u>the same</u> delimited text layer and
specify its CRS to be EPSG:100004, keep Project CRS on the fly
"off".<br>
Result:<br>
<blockquote>Image is inverted (A is South of L) and B & C
are West of A. <br>
Coordinate values are both +ve numbers and mouse position
coords decrease to West and South</blockquote>
</li>
<li>Using above data, Set Project CRS (on the fly = YES) to same
EPSG:100004<br>
Result:<br>
<blockquote>No change from above.<br>
</blockquote>
</li>
<li>Simply change Project CRS to EPSG:2048 as defined earlier in
this email.<br>
Result:<br>
<blockquote>Image orientation is now correct BUT<br>
Mouse coords readout shows -ve coord values, and these values
still (numerically) DECREASE towards the West and South.</blockquote>
</li>
</ul>
<b>To close:</b><br>
<br>
If I redo both the above tests but set Project CRS before importing
the CSV layer, there is (of course) no change to the results.<br>
Even though I was not expecting changes to some of the above test
permutations, I did them all in order to pedantically wipe out any
unexpected behaviour.<br>
<br>
<br>
So, Why am I not able to work in my desired CRS orientation when
using QGIS?<br>
Is this a bug, or is it some feature that most likely may be worth
implementing?<br>
<br>
Regards to all,<br>
Zoltan<br>
<br>
<br>
<br>
<pre class="moz-signature" cols="72">--
===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
GIS and Photogrammetric Services
P.O. Box 7, Muizenberg 7950, South Africa.
Mobile: +27-83-6004028
Fax: +27-86-6115323 <a class="moz-txt-link-abbreviated" href="http://www.geograph.co.za">www.geograph.co.za</a>
===========================================</pre>
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