Covered Topics:
- Python Programming
- Using Field Calculator with Geometry Attributes
- QGIS 3.0.3 for MacOS
- Interpolated Surface
- Sources of Ortho Imagery
The June meeting was held at Interim CDA. Thanks again for their generous use of their conference room.
Newcomers
- Tien and Helena from Integral GIS came to learn about QGIS. Their clients have brought an interest in open source tools to them prompting them to learn some alternatives to Esri software.
- Clifford pointed out that QGIS 3.0 is not really ready for production work because of lack of plugins.
- Josh came looking to produce higher fidelity navigation maps for cycling, and is particularly interested in high resolution Lidar.
Python Programming
- Clifford has found a good Introduction to QGIS PyQGIS Python Programming authored by Anita Graser, who has written some excellent books.
- Clifford downloaded some data in geopackage format for the exercises given, but had some trouble opening them with QGIS 3.0. He was successful after three tries.
- The group looked at using the
help()function to learn about the QGIS objects, at the python prompt,help(iface)returned documentation on the Qgisinterface class.
Using Field Calculator with Geometry Attributes
- Peter asked for help from the group. He has data from the King County GIS Open Data Portal and wants to add longitude and latitude columns using QGIS 3.0 and feed the result into the kepler.gl data visualization tool.
- He obtained a shape file of noxious weed data
- Previously he had not been able to add the fields using QGIS 3.0 but was able to do it using
ogr2ogr. - The group explored using the field calculator in QGIS 3.0 to get the job done.
- Peter said he tried it previously with 109k records, and it never completed.
- Using $x from the Geometry group, it worked very quickly with 56 records.
- We postulate that Peter did not enter edit mode first, which is necessary, and perhaps the error messages were not coming up on top of the various open windows.
- It was suggested to use Vector -> Geometry Tools -> Add “something” but the group did not attempt that option.
- After adding the latitude and longitude, Peter used the full data set with kepler.gl.
- It did not work in Chrome on MacOS.
- It did work in Safari.
QGIS 3.0.3 for MacOS
- Clifford shared that QGIS 3.0.3 is available for mac now.
- Paul was able to successfully install it.
Interpolated Surface
- Helena shared a problem they are having trying to emulate some of their existing solutions with open source tools. They want to create an interpolated surface clipped to a region, updated every five minutes from a realtime data stream.
- Currently they are using the interpolation plugin in QGIS and then clipping the result with a polygon.
- They are trying to use the graphical modeler, but the plugins are not accessable from the graphical modeler.
- They have not been able to get adequate graphic results using the interpolation provided by GRASS.
Sources of Ortho Imagery
- Josh asked what sources of ortho imagery were available for use with QGIS.
- Paul discussed an Esri map service available from King County along with the dangers of screen scraping and that could result in an adverse reaction from the county.
Possible Topics for the Future
- Josh has been discovering a lot of data sets and using QGIS to overlay them or crop them. He is also interested in trying to georeference SVG files and import them as shape files.
If anyone has corrections or additions they would like to make to these notes please let Paul McCombs know, or submit a pull request on github