Bug report #16823
If multi threaded rendering is enabled adding a WCS Layer makes multiple GetCoverage calls
|Category:||Web Services clients/WCS|
|Affected QGIS version:||2.18.9||Regression?:||No|
|Operating System:||Easy fix?:||No|
|Pull Request or Patch supplied:||No||Resolution:||end of life|
|Crashes QGIS or corrupts data:||No||Copied to github as #:||24722|
I have a WCS Server and I use QGIS to add a WCS Layer from my WCS server. I noticed there is 1 GetCapabilities call, 1 DescribeCoverage call, and 4 GetCoverage calls that QGIS requests from my server for adding a single layer. This seems excessive. Shouldn't there be only 1 GetCoverage call?
This is running 2.18.9 QGIS on OSX.
QGIS code branch
Compiled against Qt
Running against Qt
Compiled against GDAL/OGR
Running against GDAL/OGR
Compiled against GEOS
Running against GEOS
PostgreSQL Client Version
#1 Updated by William Valencia about 4 years ago
I noticed something weird with QGIS. So when making an "Add WCS Layer" request with QGIS, I noticed that (After initial GetCapabilities and DescribeCoverage), multiple redundant calls to my WCS Server are made. The actual "Add" Button makes 12 calls to EGI. It calls 1 GetCapabilities, 1 DescribeCoverage, 4 GetCoverage and then repeats the last 6 calls for a total of 12 calls. I am unsure why QGIS makes 4 GetCoverage calls in the first place, then it repeats the last 6 calls.
#3 Updated by William Valencia about 4 years ago
I asked the developers mailing list and included their response below. Looks like the extra 6 repeated calls are definitely a bug with multi threaded rendering. The multiple (4) GetCoverage calls may or may not be needed any more as well.
On Wed, Jul 12, 2017 at 8:29 AM, William Valencia
<[email protected]> wrote:
I noticed something weird with QGIS. So when making an "Add WCS Layer"
request with QGIS, I noticed that (After initial GetCapabilities and
DescribeCoverage), multiple redundant calls to my WCS Server are made. The
actual "Add" Button makes 12 calls to my WCS Server. It calls 1
GetCapabilities, 1 DescribeCoverage, 4 GetCoverage and then repeats the last
6 calls for a total of 12 calls. I am unsure why QGIS makes 4 GetCoverage
calls in the first place, let alone the repeated last 6 calls for the total
of 12 calls. Anyone know why QGIS is doing this?
I am not the author of the WCS provider, but I have some leads... the
extra GetCoverage calls are used for detection of some server
behaviors, from the code comments it looks like at some point there
were incompatibilities among WCS server implementations that lead to
addition of these checks to work around the incompatibilities. Not
sure if these checks are still necessary with the current versions of
For the repeated calls, this a side-effect of introduction of
multi-threaded rendering since QGIS 2.4. WCS provider get cloned for
use in worker thread, but the cloning is sub-optimal - it does not
pass the downloaded capabilities, so cloned provider has to fetch that
again. It should not be hard to fix (I have fixed that for WMS in the
initial work, but WCS provider had low priority at the time).
#4 Updated by Giovanni Manghi almost 4 years ago
- Subject changed from Adding a WCS Layer makes multiple (4) GetCoverage calls. to If multi threaded rendering is enabled adding a WCS Layer makes multiple GetCoverage calls
- Status changed from Feedback to Open
- Operating System deleted (
MacOS Sierra 10.12.5)
#5 Updated by Giovanni Manghi over 2 years ago
- Resolution set to end of life
- Status changed from Open to Closed
End of life notice: QGIS 2.18 LTR
QGIS 3.4 has recently become our new Long Term Release (LTR) version. This is a major step in our history – a long term release version based on the massive updates, library upgrades and improvements that we carried out in the course of the 2.x to 3x upgrade cycle.
We strongly encourage all users who are currently using QGIS 2.18 LTR as their preferred QGIS release to migrate to QGIS 3.4. This new LTR version will receive regular bugfixes for at least one year. It also includes hundreds of new functions, usability improvements, bugfixes, and other goodies. See the relevant changelogs for a good sampling of all the new features that have gone into version 3.4
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