1. Troubleshooting
  2. WingtraPilot - Troubleshooting

Using SRTM Tiles from EarthExplorer as Custom Elevation

For some locations, WingtraPilot and WingtraHub are unable to retrieve elevation values for flight planning. In this article, we go through an alternative method for acquiring elevation data.

To assist in flight planning, both WingtraHub and WingtraPilot use an API that fetches elevation data collected by the Shuttle Radar Topography Mission (SRTM). However, there are certain locations where this API fails. As a workaround, this process details how you can manually download the SRTM tile that you need and prepare it for import as a custom elevation data layer.

Workflow Prerequisites 

For this workflow, we will be using the EarthExplorer service managed by the US Geological Survey. This platform provides a user-friendly interface for downloading various publicly available GIS datasets.

You will have to create an EarthExplorer account to download the datasets that you need. Note that the service is free of charge.

In addition to EarthExplorer, you will also need a GIS software to modify the SRTM tile to an appropriate custom elevation dataset format. Here, QGIS will be used as it is an accessible open-source platform.

Acquiring the SRTM Tiles in EarthExplorer

Once you open EarthExplorer and log into your account, the first step is to delineate your area of interest so that the SRTM tiles that cover this region can be selected. There are two recommended ways to go about this, which are highlighted in the screenshot below.

The first option is to upload a KML or a shapefile of your region of interest. This is the best option as it will ensure that the tile fetched covers the entirety of the flight plan.  In the absence of a KML or shapefile, the second option is to manually add in coordinates (latitude and longitude) to pin the region. 

Once you've demarcated the area, go to the Data Sets tab so you can select the data layer that you need.

In the Data Sets tab, navigate to Digital Elevation, go to SRTM and select SRTM 1 Arc-Second Global. The other layers under SRTM are derivative products with coarser resolution, down to 3 Arc-Seconds. After choosing the layer, click on the Results button to retrieve the relevant tiles.

Upon clicking on Results, you'll find the SRTM tile where your flight plan falls in. To download it, click the button highlighted below and select GeoTIFF when asked for the file format in the download options.

Preparing the Dataset for Custom Elevation Import

Before you can import the SRTM tile as a custom elevation layer, some adjustments need to be done in QGIS. By default, the tile will have WGS 84 as its projection. This means that the horizontal units will be in decimal degrees. As noted in the linked article on custom elevation, the units have to be in meters for the import to work. This means that the tile needs to be reprojected to a different CRS, specifically WGS UTM. To do this, start by opening the file in QGIS.

We will be using the QGIS Warp tool to reproject the tile to the appropriate WGS 84 UTM datum. To find this tool, go to RasterProjectionsWarp (Reproject).

In the prompt that opens, you first have to set the Target CRS. As mentioned, you will be projecting to WGS 84 UTM. This website simplifies the determination of the appropriate UTM zone. Start by choosing a random coordinate within the SRTM tile. After which, add this coordinate (latitude and longitude) on the address bar of the linked site. This will then display the UTM zone you need.

For the SRTM tile used as an example in this workflow, the corresponding UTM Zone is 32 N so this is selected among the options in QGIS.

After selecting the target projection, scroll down to set the output file resolution to 30.1 since this is the equivalent of the 1 Arc-Second in meters. Finally, designate the output location and filename.

Now you have an elevation dataset that follows the requirements of WingtraHub and WingtraPilot. To import it, follow the instructions in this article.