How do I create a geospatial PDF?

Intro

Custom Terminal Procedures and Charts can be great tools for use in ForeFlight Mobile EFB. These files are commonly found in the standard PDF format. However, a standard PDF many not contain the geospatial data necessary to allow that procedure to be displayed as a Map Layer. A Geospatial PDF (geoPDF) file is one that contains the necessary geospatial data to allow those charts to be imported and displayed on ForeFlights Moving Map. 

In order to create a geoPDF, you will need to add the geospatial data to the existing file. GIS Software options such as Avenza MAPublisherTerraGo Composer, and QGIS are available for accomplishing this task. ForeFlight supports both the Adobe and OGC geospatial standards for geoPDF files.

 

QGIS Example

This article will cover georeferencing a terminal procedure using the free, open-source program called QGIS. This same process can be applied to any map in a Spherical Mercator Projection with a Coordinate System using WGS84:4326. Note that larger files will be harder to reference as "projection error" is greater toward the edges of the map. A tip is to limit the map to an E/W size of 7 minutes Lattitude and a N/S size of 5 minutes Longitude, 1:500,000 scale. 

 

Setup

We recommend downloading the Long Term Release version. Once you have the program installed, you will need to verify that the plugin, Georeferencer GDAL is currently installed. This plugin is found by going to RASTER > GEOREFERENCER in the Raster menu at the top of the page. If you do not see the Georeferencer option, add the Georeferencer GDAL plugin, by select going to PLUGINS > MANAGE AND INSTALL PLUGINS. Search for GEOREFERENCER GDAL. Once you see it in the list, make sure it is installed and that the box is checked to the left of its name. 

Georeferencer_Plugin.png

Image 1. Install the Georeferencer GDAL plugin and check the box next to it.

 

GeoReferencer

Once the plugin is installed, begin a new project and select RASTER > GEOREFERENCER.  

Georeferencer.png

Image 2. Open a new project and select RASTER > GEOREFERENCER. 

Once the Georeferencer opens, click on the OPEN RASTER button to choose your terminal procedure. 

File_Selection.png

Image 3. Select OPEN RASTER and choose your file.

NOTES: QGIS does not support the direct georeferencing of a PDF file.  You will first need to convert the PDF file to an image format. We suggest either a JPEG or TIFF file. Your file may have been produced with a large white border, this border is crucial for the correct scaling to occur on the plate. You can remove the white border later in the process.

After you select OPEN, you MAY see a Coordinator Reference System Selector popover. Make sure WGS 84 EPSG:4326 is selected and then choose OK.

CRSS.png

Image 4. Select WGS 84 EPSG:4326 and then select OK.

After your plate has opened in the Georeferencer, you MAY see a window to add Lat/Long values. Click CANCEL. Use the ADD POINT button to define at least four easily identifiable points on your plate using Lat/Long values. If you don't see the Lat/Long entry window, it may be behind your Georeferencer window. The more precise you are, and the more points you specify, the more accurate your plate georeferencing will be.

Define_Points.png

Image 5a. Define a minimum of 3 Lat/Long points on the plate.

We recommend defining the waypoints that make up your approach. The coordinates of these waypoints are normally provided by the Procedures' Designer. If the waypoints are published by the FAA, we suggest entering them into ForeFlight to find the Lat/Long for each point. Decimal Degrees (DD:dd°) is the best format for entering waypoint coordinates.

The following procedure will help locate the waypoints positions to the 5th decimal point in ForeFlight. We will use the RNAV RWY14 Approach into KHPY for our example. 

HPYRNAV14.jpg

Image 5b. Example Procedure Plate.

Enter each of the four waypoints into the FPL window in ForeFlight. Tap on the waypoint and choose Show on Map. An info window will show you the coordinates of that location. If you have your map units set to DD:dd°, this window will only display to the second decimal. To get a more accurate point, you may need to use Google Earth or go to the FAA FIX/WAYPOINT SITE at   https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/loc_id_search/fixes_waypoints/.

 

After defining a minimum of 4 points, click the TRANSFORMATION SETTINGS button and verify the following settings:

-Transformation Type is set to LINEAR.

-Resampling Method is set to NEAREST NEIGHBOUR.

-Target SRS is set to EPSG 4326: WGS 84.

-Check the box for "Load in QGIS when done."

Transformation_Settings.png

Image 6. Transformation Type is set to LINEAR. Resampling Method is set to NEAREST NEIGHBOUR. Target SRS is set to EPSG 4326: WGS 84. Check the box for "Load in QGIS when done."

After verifying the Transformation Settings, click on the START GEOREFERENCING button.

Start_Georeferncing.png

Image 7. Select START GEOREFERENCING.

 

Saving the geoPDF (Without removing white border)

Once georeferencing is complete, the plate will be copied from the Georeferencer to the QGIS home page. From the home page, select RASTER > CONVERSION > TRANSLATE (CONVERT FORMAT). 

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Image 8. Select RASTER > CONVERSION > TRANSLATE (CONVERT FORMAT).  

Selecting Convert Format will open a new window. Select the Converted "..." button and choose SAVE TO FILE. Specify the destination and verify PDF FILES (*.PDF) is selected as the exported file type. Select SAVE. Select RUN in the Translate (Convert Format) window. Your plate will be exported as a geospatial PDF that can be used in ForeFlight. *Mac users may see a warning saying that the action could not be completed, but the PDF file should be located in the location you selected above. 

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Image 9. SAVE TO FILE > Choose Destination > Specify PDF FILES (*.PDF) as export format.

 

Saving the geoPDF (While removing the white border)

To remove the extra border around the plate or the areas of the map you wish to not display, go to RASTER > EXTRACTION > CLIP RASTER BY EXTENTA02ABA60-82E3-4475-B876-DB4E80CBA8FD.png

Image 10. Steps to Remove the White Border and save geoPDF file.

Click on the "..." in the Clipping Extent row and choose Select Extent on Canvas. Now click to the Chart to create a cropping window. Select the area that you wish to see in your file. Finally, tap on the "..." on the Clipped Row and choose the path for the file to be saved to. Now Run the Extractor. *Mac users may see a warning saying that the action could not be completed, but the PDF file should be located in the location you selected above.