The mapping process described here has six steps.
- Set up QGIS interface
- Load satellite image layers from the Web Map Service (WMS)
- Check the geographic projection of your QGIS project.
- Download the auto-mapping segments
- Create a new polygon shapefile that will contain your burnt area mapping
- Copy burnt areas from the auto-segments to the new burnt area mapping shapefile
- Setup QGIS interface
To set up QGIS for mapping you need to make sure you have the browser and layers windows active. If you can not see these windows right click on the top bar and selct the panels as shown below:
2. Load satellite image layers from the Web Map Service (WMS)
To begin mapping you first need to load the Sentinel-2 satellite image layers from the Web Map Service (WMS). In the browser panel find the WMS/WMTS layer and right click to choose “New Connection”.
Now you need to add a name to the connection and the URL link. The URL link for the Darwin imagery is currently:
Copy and paste the above URL into the URL section.
Note that this address may change in the future but the correct address will always be updated here.
The current state of the Web Map Tile Server (WMTS) is as shown below:
If WMTS is already saved in QGIS and expanding it shows the old layout. Try to:
⦁ Right-click on the NTRRP name and select ‘refresh’
⦁ If it is not working, click on the QGIS top menu ‘Settings’, selected the menu entry ‘Options’. The following window should pop up:
Select the side tab ‘Network’ and hit the trash bin icon (red) to delete the cache. While you at it, make sure to set the cache expiry time (General section) to a few hours or a day. The WMTS will be updated every five days. You want the cache to expire before then, so the layer names are properly updated.
The layers web tile layers contain the following images.
- DRW_dMIRB_T12 – DRW (Darwin Region) dMIRB (difference middle infrared burn ratio) T12 (Time 1 – Time2)
- DRW_dMIRB_T13 – DRW (Darwin Region) dMIRB (difference middle infrared burn ratio) T12 (Time 1 – Time3)
- DRW_NATURAL_COLOURS – T1 (Tile one) DRW (Darwin Region) Natural_Colours
The layer names now included timepoint (a.k.a. sentinel-2 satellite overpass) date in the format YYYYMMDD. Timepoints are ordered by decreasing dates, T1=9 May 2021, T2= 4 May 2021 ….
DRW_NATURAL_COLOURS can be used as a base map. This is the latest overpass.
So DRW_dMIRB_T12 shows the burnt areas between the previous week (overpass) and the latest overpass. Burnt areas are clearly highlighted in red.
DRW_dMIRB_T13 shows the burnt areas between the week before last and the current week. These two time periods are used to reduce the impact of cloud that may obscure part of an image during and overpass. In the image below
3. Check the geographic projection of your qgis project.
Each layer is now available in two projections (it is kind of a trial). At this stage it is best to use the EPSG:32752 (UTM Zone 52S) WMTS layers. Usually, the first layer displayed in QGIS will set the project default projection. QGIS displays a project default projection at the bottom-right corner of the main window, like this:
If it is not showing the correct projection you need to set this manually. Under the project top menu select ‘Properties’.
Use the projection code ‘32752’ to selct the UTM zone 52 projection as shown below:
4. Download the auto-mapping segments
You then need to download the auto-mapping segments for the tile area you are about to map. The tile areas are shown here:
The current location for the image segmentation downloads is here: https://test.firenorth.org.au/ntrrp
Once you download the zip files for your area of interest, unzipp and navigate to the folders in the QGIS browser.
Folder T12 contains the auto-map polygons for the last week. Folder T13 contains the polygons for the last two weeks. In each folder, there are three polygon files.
New naming convention:
where, the first date string is the T1 overpass date, and the second date string is the T2 overpass date.
- The files ending seg_150 contains polygons for just the main burnt areas. This is the main file you will use.
- The files ending seg_100 contains polygons for all burnt areas including some burnt areas that maybe less clear. This file is also more likely to contain many more polygons that are not fire at all.
- The files ending seg_250.shp contain less polygons.
To load the polygons into QGIS just double click them from the QGIS browser window.
Make the infill of the polygon transparent by:
- Double clicking on the auto-map polygon layer to open the payproperties window. Make sure you have the ‘Symbology’ window seltected.
- Click on ‘Simple Fill’
- set the Fill Style to ‘No Brush’. The click ok
5. Create a new polygon shapefile
Now you need to create a new polygon shapefile that you will copy your mapped fire layers into. In the top menu select the Layer menu then ‘Create Layer’ and finally ‘New Shapefile Layer’ as shown below.
Save your new shapefile in a working directory on your computer. Make a directory that you use for all your fire mapping. Give the shapefile and the folder you save it in a name following the following naming convention.
Start with ‘FSDWN’ (this stands for fire scars Darwin) then the mapping period from the first image date to the second image date. For example FSDWN_20210419-20210423. This allows others to know where and when the mapping was conducted.
6. Copy burnt areas from the auto-segments to the new burnt area mapping shape file.
Now make the new file editable by clicking the edit (pencil) button.
Now activate the selection tool and use the cursor to draw a box around some polygons covering a burnt area to select them
When selected they will appear yellow.
Now copy the selected features either through the edit menu item or using ctrl+c.
The copied polygons should now appear in the final mapping layer you created.
Continue selecting, copying and pasting all the burnt areas you can identify into the final map shape file. It is good partice to save your edits as you work and when you have finished.
Once you have finished the mapping the next step is to give the mapping layer some identifing information and upload it to NAFI. This is explained in the next section.