[Qgis-user] Layer Ordering for KMZ

Sun Aug 15 06:53:56 PDT 2021

I just had a chance to look at the samples and it seems my hypothesis was
in fact correct.

I had expected that because Google Earth functions in 3D that it may
perhaps render placemarkl symbols based on the orientation of the "camera"
to the point, but from my assessment it definitely seems that altitude is
the deciding factor when it comes to determining the rendering order of
symbols.

By exporting the big points with "clamptoground" active, but using the
relative to ground and altitude addend functionality in the KML tools
export (see screenshot.png), the small points are "higher" in altitude and
render on top of the big points regardless of orientation. In the example I
provided (desired_output.kmz) I "lifted" the small points 25m off the
ground.

By using the $x and $y attributes on the supplied shp data in QGIS, it
became apparent that there were some offsets between the point positions:

Small Points Big Points
wkt_geom id Name x y wkt_geom id Name x y
Point (-98.94705168629492675 29.6341226203915511) 1 A -98.94705168629493
29.63412262039155 Point (-98.94705168490899894 29.63412262285223875) 1 E
-98.947051684909 29.63412262285224
Point (-98.93203732506144377 29.63666293420626374) 2 B -98.93203732506144
29.636662934206264 Point (-98.9320373399207682 29.63666292869620733) 2 F
-98.93203733992077 29.636662928696207
Point (-98.94352477360057208 29.62202767741294451) 3 C -98.94352477360057
29.622027677412945 Point (-98.94352558873751491 29.62202773383394927) 3 G
-98.94352558873751 29.62202773383395
Point (-98.92999000422139488 29.62559164108440513) 4 D -98.9299900042214
29.625591641084405 Point (-98.92998992924056267 29.62559174501802062) 4 H
-98.92998992924056 29.62559174501802

I expect the reason "some" points rendered on top and not others, is that
the slight positional offset would have likely ended up giving the points
different altitudes based on the "clamp to ground" positions.

There are a number of approaches you can utilise to resolve this issue,
depending on your needs. One is to export the KMZ with a multilayer symbol
from QGIS (the style will become a single png), if you intend on using the
same geometries. This would yield a more consistent result, however it of
course would not work on different layers.

I have attached a zip file (kmz_data.zip) with the following elements for
your review:

   - screenshot.png - KML Tools export settings for increasing point
   position from ground
   - desired_output.kmz - The desired output as expressed by OP
   - points_big_clamped_to_ground.kmz - Big points layer exported with
   clamp to ground and used in desired output
   - points_single_symbol_one.kmz - A multilayer QGIS symbol used in a KMZ
   - points_single_symbol_one.qml - A QML style for anyone unfamiliar with
   multisymbol styles
   - points_single_symbol_two.kmz - A multilayer QGIS symbol with offset
   applied to get a style closer to original kmz
   - points_small_with_altitude.kmz  - Small points layer exported with
   relative to ground and addended altitude, used in desired output
   - points_with_shift.kmz - Point positions shifted west to display how
   altitude seems to impact rendering in google earth more than orientation

The export tools also provide various data driven options which may be used
instead of the addend altitude feature.

Hope that clears this up for everyone. I'd be interested to know if this
resolves the issues that were being experienced.

Regards

On Sun, 15 Aug 2021 at 05:04, David Strip <qgis-user at stripfamily.net> wrote:

> I tried your file on   Google Earth Pro 7.3.4.8248 (64-bit) on Win10. I
> get an even stranger result - two of the small circles appear on top of the
> big circles, the other two behind.
> Both layers are listed as clamp to ground.
>
>
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