Process Maps, NDVI and 3d Models for Free

Process Maps, NDVI and 3d Models for Free

With the Drone Data Management System™ officially out of beta testing, I thought it would be helpful to go through and show new users how they can still use it to process orthomosaics, NDVI maps and 3d models with imagery from any drone for free. This isn’t intended to be a comprehensive guide to mapping techniques, but I’ll go through the basics for the sake of those with no experience. If you already have some data you’re ready to try, skip to the post-processing section below.

Data Collection

First of all, to make any map, you need to collect the right kind of imagery. For a drone, that means collecting images that point almost straight down and overlap at least 60% with its nearest neighbors front and back as well as side to side. In other words, if your camera has a field of view of 100 meters on the ground along the path of travel, it should move only 40 meters between shots. In general, 60% is an adequate overlap balancing coverage and avoiding excessive data collection, which slows down processing.

Planning for overlap and sidelap for Pixhawk vehicles is straightforward if you use the Mission Planner Survey (Grid) function. You can read more about that here: ArduCopter Wiki

DJI doesn’t provide planning tools for surveying missions, but some third parties do offer these features for the Phantom 3, 4 and Inspire 1. The UgCS app, for example, lets you plan a mission on a PC and then load it onto your drone. UgCS is free for private use and supports automated survey mission planning with camera and drone presets for DJI vehicles.

If your drone doesn’t have a gimbal, do your best to fix the camera pointing straight down. This might mean aiming a little forward to compensate for a multirotor’s pitch in flight. Most drones in ordinary weather conditions should be able to maintain adequate overlap. DDMS compensates for small angles off vertical that may be in some images.

Once you’ve collected all the raw images, give them a quick look. Make sure they aren’t blurry, don’t have part of your drone in frame, and that they appear to have significant overlap. It’s not necessary to geotag your imagery before processing, but there are advantages to doing so if you can. It speeds up processing, scales your map, reduces warping artifacts and makes it possible to take measurements from your orthomosaic. If your drone is running on Pixhawk and you’ve triggered your camera using the distance trigger function, DDMS can automatically geotag your images if you upload the telemetry log (.tlog) with your images. DJI drones automatically add geotags to each image.

Post-Processing

Uploading to DDMS is simple. First, sign up here using just an email address. Then log in and click Create Mission. Enter a description for your mission and select the images and supporting files (.tlog) from your flight. Then just click Upload. At this point, your job is done, leave your browser open on this page until it prints a message that all images have been uploaded successfully!

To add NDVI or a 3d model to your mission, open the Missions Page in a new browser tab, select your mission and click the Analyze Images button. Be sure to leave the upload page open until it finishes. On the Analysis page, you’ll have the option to add NDVI and 3d Model generation. More apps are available with a paid membership.

AppsPage

Sample “Analyze Images” Page, Select Apps Here

Our NDVI process is optimized for NGB (NIR, Green, Blue) converted cameras such as our own custom filters/cameras and similar options like those from MaxMax. Some converted cameras, particularly the small, cheap ones, have serious problems with rolling shutter distortions. These distortions make stitching much more difficult as they aren’t consistent like the distortions from a lens, so try to check out some sample imagery before choosing a camera.

DDMS will take all your images and automatically process them into a 10cm/pixel geotiff (higher resolution available with paid memberships). If geotags are included, the mosaic will be georeferenced. It also automatically tiles your map for viewing online using Map Viewer. You can download the raw geotiff and NDVI mosaic for offline viewing by clicking Access Downloads on the mission page. Often times these files are too large for ordinary picture viewing software to open. QGIS or GlobalMapper are good options for offline viewing of geotiffs, but it’s almost always slower to work with these large files offline.

The Analyze Images page also shows you the status of each step of processing as it progresses. When each step reaches ‘Ready’ status, you can access the result by clicking directly on it. In Map Viewer, toggle between the ortho-mosaic and NDVI results by selecting the layer from the upper-right corner and adjusting the opacity slider.

WinterWheatSidebySide

Composite of two Map Viewer Windows, Raw NGB Orthomosaic on Left, NDVI on Right

DDMS also recreates a 3d model of each mission. Select the 3d Model app and download the files to explore using Sketchfab, Meshlab or another modeling package.

Roof1
by Event38
on Sketchfab

Although the beta period is over, we are still actively seeking feedback from the community. We see a lot of users doing things we didn’t expect them to do with drone maps and we want to keep encouraging that kind of experimentation!

You can read more about the Drone Data Management System™ here. We have more apps available for the Pro and Advanced tiers, like DVI, 3d PDF, DSM, KMZ, Volume Calculation and Point Cloud Exports.


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