News of debris discovered off the coast of Reunion Island and the subsequent acknowledgment from the Malaysian Prime Minister has given hope as to the whereabouts and fate of Malaysia Airlines Flight 370. While we wait for additional information regarding the missing Boeing 777, I wanted to examine if GIS could add plausibility that debris may have washed up this far West from the original search areas.
According to the experts, it is possible that both deep ocean currents and wind-driven surface currents could have moved the debris the some 2600 miles from the search area to the coast of a small island just east of Madagascar. More specifically, the Indian Ocean Gyre, a large system of rotating ocean currents known to move ocean trash and debris long distances across the globe, could be partly responsible for the movement of the debris.
The Indian Ocean Gyre is composed of two major ocean currents, the South Equatorial Current, and the West Australian Current. A quick Google search for Ocean Currents yields several good maps that illustrate the gyre very well. So I wanted to try and overlay some ocean current and prevailing winds graphics on top of some additional vector data I had of the MH370 search areas and potential flight path (click the links for reference images and data).
To align the graphics with the vector data we need to perform a process called georeferencing. *Performing georeferencing inside QGIS is possible through a native plugin called the Georeferencer GDAL plugin.* “Native”, meaning the plugin is already installed and you simply need to turn it on.
Once turned on, you can access the Georeferencer plugin from the Raster dropdown > Georeferencer > Georeferencer which will bring up the Georeferencer window.
The usual procedure for georeferencing an image involves selecting multiple points on the graphic, and then tying those points to ‘real world’ locations in the map.* We call these points control points.* The more control points you create, the better the result will be.* The first step is to load the graphic you want to georeference on top of your vector data.
The image will load into the Georeferencer window and you can begin the process of selecting control points to line up the image with the real world.
There are two ways of creating control points: we can manually enter them, or we can choose them interactively by clicking on the map.* With the Control Points tool active, click a point on the graphic.* Then, either enter the coordinates of where that point should be on earth, or click the location in the vector data that corresponds to the location in the graphic.
Now the georeferencing will occur when the GIS warps the graphic according to the control points in a process known as transformation.* Depending on the transformation or warping method you use, you will need a minimum of between 4 and 10 points.* We are going to use a Polynomial 3 transformation (for more information on transformation algorithms, I encourage you to review “Available Transformation Algorithms” here), which requires a minimum of 10 control points to work correctly.* *The control points will show up in the chart at the bottom of the georeferencer window called the GCP (ground control point) Table.
Once your control points are selected, we need to configure some settings for the transformation to work correctly.* Open the Transformation Settings window under the Settings drop down.
For starters, set the Transformation Type to be Polynomial 3.* Then make sure the Resampling Method is set to Nearest Neighbor, and Compression is set to NONE.* Next, choose a name and location for the georectified graphic.* Set the Target SRS to be the spatial reference you want the output graphic to be, and check the box to Load in QGIS when done.* The settings should look similar to the graphic below.
When you are finished click OK to dismiss this dialog box.* We are now ready to start the transformation.* To do this, click the File dropdown > Start georeferencing.
When the process is done, it will add the warped graphic to the map.
I added some transparency to the now warped graphic so we could see how well it lines up with my vector country layer.* Looks pretty good.* Now all we need to do is digitize the currents as line features, add labels, and color code based on temperature.
I repeated the process for the second graphic of prevailing winds in the region.* The digitized results from both can be seen below along with the original search areas, and the location of Reunion Island.
The now georeferenced and digitized graphics illustrate how the debris could have washed on shore as the surface currents rotating around the Indian Ocean Gyre could have move the debris in a general Western direction.* Now, let me reiterate that I am not an expert on ocean currents or aircraft search and rescue, and I don’t wish to make claims about MH370.* This is an opportunity based on real-world examples to examine how to use QGIS to overlay information from a graphic on top of other vector data using the Georeferencer GDAL plugin.
It will be interesting to see whether or not the experts use their early findings to help to refine additional search areas.* If you are interested in trying the exercise for yourself, you can download the graphics from the links embedded above.
The post Georeferencing Imagery in the Hunt for MH370 appeared first on Boundless.
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According to the experts, it is possible that both deep ocean currents and wind-driven surface currents could have moved the debris the some 2600 miles from the search area to the coast of a small island just east of Madagascar. More specifically, the Indian Ocean Gyre, a large system of rotating ocean currents known to move ocean trash and debris long distances across the globe, could be partly responsible for the movement of the debris.
The Indian Ocean Gyre is composed of two major ocean currents, the South Equatorial Current, and the West Australian Current. A quick Google search for Ocean Currents yields several good maps that illustrate the gyre very well. So I wanted to try and overlay some ocean current and prevailing winds graphics on top of some additional vector data I had of the MH370 search areas and potential flight path (click the links for reference images and data).
To align the graphics with the vector data we need to perform a process called georeferencing. *Performing georeferencing inside QGIS is possible through a native plugin called the Georeferencer GDAL plugin.* “Native”, meaning the plugin is already installed and you simply need to turn it on.
Once turned on, you can access the Georeferencer plugin from the Raster dropdown > Georeferencer > Georeferencer which will bring up the Georeferencer window.
The usual procedure for georeferencing an image involves selecting multiple points on the graphic, and then tying those points to ‘real world’ locations in the map.* We call these points control points.* The more control points you create, the better the result will be.* The first step is to load the graphic you want to georeference on top of your vector data.
The image will load into the Georeferencer window and you can begin the process of selecting control points to line up the image with the real world.
There are two ways of creating control points: we can manually enter them, or we can choose them interactively by clicking on the map.* With the Control Points tool active, click a point on the graphic.* Then, either enter the coordinates of where that point should be on earth, or click the location in the vector data that corresponds to the location in the graphic.
Now the georeferencing will occur when the GIS warps the graphic according to the control points in a process known as transformation.* Depending on the transformation or warping method you use, you will need a minimum of between 4 and 10 points.* We are going to use a Polynomial 3 transformation (for more information on transformation algorithms, I encourage you to review “Available Transformation Algorithms” here), which requires a minimum of 10 control points to work correctly.* *The control points will show up in the chart at the bottom of the georeferencer window called the GCP (ground control point) Table.
Once your control points are selected, we need to configure some settings for the transformation to work correctly.* Open the Transformation Settings window under the Settings drop down.
For starters, set the Transformation Type to be Polynomial 3.* Then make sure the Resampling Method is set to Nearest Neighbor, and Compression is set to NONE.* Next, choose a name and location for the georectified graphic.* Set the Target SRS to be the spatial reference you want the output graphic to be, and check the box to Load in QGIS when done.* The settings should look similar to the graphic below.
When you are finished click OK to dismiss this dialog box.* We are now ready to start the transformation.* To do this, click the File dropdown > Start georeferencing.
When the process is done, it will add the warped graphic to the map.
I added some transparency to the now warped graphic so we could see how well it lines up with my vector country layer.* Looks pretty good.* Now all we need to do is digitize the currents as line features, add labels, and color code based on temperature.
I repeated the process for the second graphic of prevailing winds in the region.* The digitized results from both can be seen below along with the original search areas, and the location of Reunion Island.
The now georeferenced and digitized graphics illustrate how the debris could have washed on shore as the surface currents rotating around the Indian Ocean Gyre could have move the debris in a general Western direction.* Now, let me reiterate that I am not an expert on ocean currents or aircraft search and rescue, and I don’t wish to make claims about MH370.* This is an opportunity based on real-world examples to examine how to use QGIS to overlay information from a graphic on top of other vector data using the Georeferencer GDAL plugin.
It will be interesting to see whether or not the experts use their early findings to help to refine additional search areas.* If you are interested in trying the exercise for yourself, you can download the graphics from the links embedded above.
The post Georeferencing Imagery in the Hunt for MH370 appeared first on Boundless.
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