#663: Zooming in too far causes vector weirdness
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Reporter: epatton | Owner: grass-dev@lists.osgeo.org
Type: defect | Status: new
Priority: normal | Milestone: 6.4.0
Component: default | Version: unspecified
Keywords: | Platform: Unspecified
Cpu: Unspecified |
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While editing some polygons in a Lat-Long location in Grass 6.5, I noticed
that zooming in too far causes the vector boundaries to suddenly shift
direction at wildly different angles. I can't determine at what scale this
seems to occur, as the map scale isn't displaying correctly either (it
only shows 1:0 at all zoom levels, even when zoomed to full extent of
map).
I'll attach a few screenshots showing the transition from the normal
polygon to where the display error occurs.
I forgot to mention that in some cases, such as the attached
Polygon_after_zooming.png, some vector elements simply vanish rather than
display at incorrect angles.
#663: Zooming in too far causes vector weirdness
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Reporter: epatton | Owner: grass-dev@lists.osgeo.org
Type: defect | Status: new
Priority: normal | Milestone: 6.4.0
Component: wxGUI | Version: svn-develbranch6
Resolution: | Keywords:
Platform: Linux | Cpu: x86-64
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Comment (by hamish):
this is a very, very, very, very old bug. Try filled polygons for more
weirdness. (I had a quick look on the old RT bug system but didn't see an
open ticket, anyway it dates back at least before 5.0.0) The real question
is if it is still present in the new GRASS 7 display library.
> I can't determine at what scale this seems to occur, as the map
> scale isn't displaying correctly either (it only shows 1:0 at
> all zoom levels, even when zoomed to full extent of map).
FWIW a 1:x map scale is fairly useless/wrong on a monitor. It's
only really of use on a printed page of fixed size. To calculate it
correctly you need to know the exact dpi and dimensions of the monitor,
and X-Windows (if available) only gives you an untrusted guess at that.
The GIMP provides a calibration GUI where you put a ruler up to the scale
on the screen and you type in the number of millimeters between the marks
on the screen. While it is somewhat useful for giving you a quick idea of
the map extent, it presents the user with a misleading sense of precision,
and I find shipping known-bad data to be unpleasant. Also for lat/lon I
expect the x and y axes being of different scales away from the equator
makes the concept even more absurd.
better to follow the changing coordinate values as you move the mouse
around.