[gdal-dev] Report on GEOS maintenance grant

[Daniel Baston]

Hi All,

As February comes to a close, I’m winding down the GEOS maintenance work
that the GDAL PSC funded in 2022 [1]. I appreciate the opportunity to do
this work and am especially thankful to those who reported issues, reviewed
pull requests, or participated in discussions about this work.

For anyone who’s interested, I wanted to share a few of the highlights from
my perspective.

New functionality: GEOS now supports reading, writing, and overlay of
geometries with an M dimension. I added a number of C API utility functions
requested by client library developers: GEOSLineSubstring,
GEOSEqualsIdentical, and thread/context-specific interrupt handlers. I also
brought in clustering algorithms such as DBSCAN that were previously only
available in PostGIS.

Performance enhancements: I found some nice performance wins in key GEOS
algorithms such as geometry intersection testing (GEOSIntersects and
GEOSPreparedIntersects), distance (GEOSPreparedDistance and
GEOSPreparedDistanceWithin) and buffering complex geometries. There are
also some gains in core internal classes such as CoordinateSequence and
STRtree that deliver across-the-board gains.

Project maintenance. I was able to simplify our CI setup by removing the
use of Azure and AppVeyor services and bringing the associated environments
into GitHub Actions, write a harness for performance testing and
visualization, and perform code cleanup such as migrating from raw to
managed pointers in key classes. I resolved a number of long-standing bug
reports with WKT input/output, geometry simplification, and
crashes/incorrect results from multiple algorithms in edge cases such as
empty geometry inputs.

Not everything panned out, or at least not yet. Something we’ve wanted in
GEOS for a long time is the ability to create a GEOS geometry directly from
an external memory buffer, such as a PostGIS LWGEOM or a GDAL OGRGeometry
(“zero-copy”). I added experimental support for this, but so far I haven’t
found a case where it offers much performance benefit.

Dan

[1] https://lists.osgeo.org/pipermail/gdal-dev/2022-February/055433.html
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