Hi Devs,
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.
QGIS version in use by me, as per attached screenshot.
*The problem:*
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.
Furthermore, when I move the mouse downwards or to the left, the
coordinate readout values decreases instead of increases.
In short, if I work in a South Oriented CRS, I must deal with an
inverted picture or an incorrect coord readout.
Is this correct behaviour for QGIS?
*_To test:_*
*
Fixed test parameters:*
* Always start with a "new" QGIS so that only default project settings
are "set". (EPSG:4326 but 'on the fly CRS' off)
* Only load the CSV file so that there are no other map layers to to
contend (CRS wise) with.
* The absolute position (on earth) of the test data is not important -
we are looking to see that QGIS displays the points
correctly_relative to each other_, and that the coordinate readout
is correctly increasing South and Westwards.
* Use only the two following CRS (note the only difference is the axis
parameter)
*EPSG:2048* is +proj=tmerc +lat_0=0 +lon_0=19 +k=1 +x_0=0
+y_0=0 *+axis=wsu* +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
*USER:100004* is +proj=tmerc +lat_0=0 +lon_0=19 +k=1 +x_0=0 +y_0=0
*+axis=enu* +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
o *Testdata:*
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)
A,19961.49,3769105.30
B,19902.64,3769135.18
C,19899.91,3769132.99
L,20095.87,3769783.70
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')
*Test results:*
* Open QGIS, add delimited text layer and specify its CRS to be
EPSG:2048, keep Project CRS on the fly "off".
Result:
Image is inverted (A is South of L) and B & C are West of A.
Coordinate values are both +ve numbers and mouse position coords
decrease to West and South
* Using above data, Set Project CRS (on the fly = YES) to same EPSG:2048
Result:
No change from above.
* Simply change Project CRS to EPSG:100004 as defined earlier in this
email.
Result:
Image orientation is now correct BUT
Mouse coords readout shows -ve coord values, and these values
still (numerically) DECREASE towards the West and South.
*Start with a "new" QGIS* (to pedantically make certain that no CRS
functionality is left over from above tests)
* Open QGIS, add _the same_ delimited text layer and specify its CRS
to be EPSG:100004, keep Project CRS on the fly "off".
Result:
Image is inverted (A is South of L) and B & C are West of A.
Coordinate values are both +ve numbers and mouse position coords
decrease to West and South
* Using above data, Set Project CRS (on the fly = YES) to same EPSG:100004
Result:
No change from above.
* Simply change Project CRS to EPSG:2048 as defined earlier in this email.
Result:
Image orientation is now correct BUT
Mouse coords readout shows -ve coord values, and these values
still (numerically) DECREASE towards the West and South.
*To close:*
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.
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.
So, Why am I not able to work in my desired CRS orientation when using QGIS?
Is this a bug, or is it some feature that most likely may be worth
implementing?
Regards to all,
Zoltan
--
===========================================
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 www.geograph.co.za
===========================================
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