Michael Barton wrote:
Before we make these changes, I'd like to reiterate again what is going on
with a bit of visual display to better show the issues.1. There is not a systematic, major inaccuracy from zooming the display in
the GIS Manager.2. This inaccuracy reported only
But is there and it will bite users occasionaly, making them corrupt
their data only once a month or week.
occurs with interactive zooming when
displaying a raster map so that the raster grid squares are much larger than
the pixel size. That is, when you can see only a few grid squares in the
display.3. It affects the number of grid cells displayed, not the actual
computational or display regions.4. It is primarily (or likely entirely) a function of using g.region -a to
align the display region to the raster grid at the current resolution. I
originally did NOT use this flag, because I was concerned about potentially
uncontrolled changes to zoom precision, but added this to the zooming a few
months back at the strong request of Maciej (possibly echoed by a few
others).
Another try to blame it on me. Noticed, skipped.
Please consider that gis.m not preserving the res while zooming is as
bad as not setting the extents correctly. Neither is acceptable,
becasue either leads to wrong region settings.
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The reported problem with displaying grid cells at high magnification is
primarily or entirely a function of how g.region -a aligns the region with
the raster grid cell boundaries. I don't know how this works internally and
someone with C programming experience will have to deal with it if we want
it to work differentlySo, what do we want to do? We can either have
1. All zooming is aligned with the cell borders, matching the current
resolution, with the possible result of a bit of rounding error in the
display when zoomed in to a point where the cells are very large compared to
pixel size--due to the way that g.region -a works.OR
2. Zooming is NOT aligned with the cell borders and the current resolution.
In this case, what you see is very close to the actual region extents when
zoomed in to a point where the cells are very large compared to pixel size.
This is how I originally had it.
Both are as bad.
Maciek