QGIS expression engine has a powerful a summary aggregate function that can do spatial joins on the fly. This enables some very interesting uses.Continue reading
When you want to buffer features that are spread across a large area (such as global layers), there is no suitable projection that can give you accurate results. This is the classic case for needing Geodesic Buffers – where the distances are measured on an ellipsoid or spherical globe. This post explains the basics of geodesic vs. planar buffers well.Continue reading
You may have seen a map where source and destination points are connected via curved lines. It is possible to create such a map in QGIS with a simple trick – using custom projections and densification of lines. I will outline the steps to create such a map.Continue reading
I got a chance to attend the 3rd Annual QGIS User Conference at A Coruña, Spain.
This was the meeting point of over 100 QGIS developers, users, and trainers from all over the globe. It was the first time I met the QGIS community in person, including some of the people whose work I have admired for years. The event took place over 3 days – 2 days of workshops and 1 day of talks. I am putting some of my notes, takeways and links to resources shared on other channels (twitter, telegram, email) for the benefit of folks who were not present
I recently attended the OpenAQ workshop in Delhi . The workshop’s goal was to bring tech, science and media folks working on air quality together and brainstorm how to use open data to tackle air pollution challenges. Below are my notes and links to materials presented during the workshop.
Below are my notes and links to materials presented during the workshop.Continue reading
This weekend, I got an opportunity to volunteer with a non-profit called Junglescapes. We took a day trip to the Bandipur forest in Karnataka where they have done extensive work in forest restoration. One of their success stories is working with the locals to remove invasive species such as Lantana from the forest. Junglescapes volunteers and locals carry out regular line transact surveys to determine the impact of their interventions. One of the goals for my participation was to see if we can replace the cumbersone paper forms and handheld GPS devices with a mobile-phone based survey using ODK. I am sharing my notes on how we setup the survey and mapping of the result.
I created a survey form using XLSForm standard. The form is quite simple and uses the geopoint field type to collect the Lat/Lon of the start and end points of the transact. There is also a repeated field of type image to capture pictures along the transact. You can make a copy of this XLSForm spreadsheet and use it to customize your transact survey. Once the spreadsheet was ready, I converted it XForm using the online converter. The resulting XML file was loaded to a ODK Aggregate server running on AppEngine. Individual Android devices running the ODK Collect app were configured to use this server and forms were downloaded to the devices. You may also skip the server and copy the XML directly to mobile devices running the ODK Collect App.
Collecting Field Data
Upon entering the wildlife sanctuary, we trekked up to the region where the restoration has been done. There were 4 sites where we had to carry out the line transact survey. We lay down a 150ft line using a tape measure and collected data about number of trees, shrubs, plants and grass in a 10ft zone around the line. The data was entered directly in the ODK Collect app.
The ODK Collect app works completely offline. We were in the middle of a forest with no cell coverage but data collection work seamlessly. The app would sync the data once the devices get cell reception.
Processing Field Data
After we finished the surveys, we headed back from the sanctuary. When our devices got mobile data signals, the form submissions were submitted to the ODK Aggregate server automatically. You can also use the ODK Briefcase application on your computer to copy the data from devices directly.
Once you pull the data from the devices using ODK Aggregate or ODK Briefcase, you would have a spreadsheet with individual form submissions. This itself can be a final product of the survey and can be maintained as a record from periodic surveys. We wanted to also map the data since we had collected GPS coordinates for the start and end of each transact. This required a little bit of post-processing of the data to create a spreadsheet like this. Saving thie spreadsheet as a CSV, it can be imported in QGIS.
Using the Convert points to line tool from the Processing Toolbox, I created a line layer from the start and end points of the transact.
The resulting QGIS line layer was exported as a KML and imported to Google My Maps . I had also collected our entire trek and some waypoints using the My Tracks app. This was also imported to Google My Maps. These layers resulted in a rich and informative map from our field data exercise. See the live interactive map here.
Overall, using ODK for the transact surveys helped speed up the data collection. There was no data-entry after the surveys and creating an interactive map visualization was a breeze. If you are an individual or a team who is doing field data collection, moving to ODK would help you reduce errors and collect accurate data without the hassles of data entry.