Here is the link to my full presentation on drone use to document this process
Photogrammetry: the science of making reliable measurements by the use of photographs and especially aerial photographs (as in surveying) (1)
Digital Surface Model | Orthomosaic | Ground Sampling Distance | Point Cloud | Mesh model, using the same subject.
These have to be our top three questions from our new clients. By sharing these short explanations, they might answer some of your photogrammetry questions as well.
DSM (Digital Surface Model) is an elevation model that includes the tops of buildings, trees, power lines, and any other objects. Commonly this is seen as a canopy model and only ‘sees’ ground where there is nothing else over top of it (2)
We present here a collection of 98 2D images of an earthen dam in Northern California with a DSM heat map overlaid on top of Google earth. Blue is the lowest point and red the highest. You can clearly see where the water outlet for this dam is. Less noticeable is the uncontrolled spillway location. Hint: it is the title image of this document.
Ortho or orthoimage is an aerial photograph geometrically corrected (“orthorectified”) such that the scale is uniform: the photo has the same lack of distortion as a map. Unlike an uncorrected aerial photograph, an orthophotograph can be used to measure true distances, because it is an accurate representation of the Earth’s surface, having been adjusted for topographic relief, lens distortion, and camera tilt. (3)
Here is the same subject with an orthorectified image overlaid the latest image from Google Earth. As is the case so many times with this process, the accuracy is off. Google Earthimages are in the neighborhood of +/-30m (4), while aerial drone images from NAA are in the centimeter range typically (6). While Google Earth has great coverage for the ‘large’, the solution comes down to the high def camera on an aerial platform less than two hundred feet above the ground to get images such as the one above to cover the ‘small’.
Ground Sampling Distance (GSD) is the distance between two consecutive pixel centers measured on the ground. The bigger the value of the image GSD, the lower the spatial resolution of the image and the less visible details. The GSD is related to the flight height: the higher the altitude of the flight, the bigger the GSD value.(5)
The final image above has included: DSM and Orthro images over a Google Earth map that is geolocated. The listed partial sampling of facts below are taken directly from the generated quality report within Pix4D for this dam. Each completed project generates a report that in conjunction with a survey team produces amazing accuracy and imagery. The total time aloft to collect all of this the aerial data was less than fifteen minutes.(6)
- Average Ground Sampling Distance (GSD) 1.86 cm / 0.73 in
- Area Covered 0.074 km2 / 7.4129 ha / 0.03 sq. mi. / 18.3271 acres
- RMS Error [m] 0.415261 0.650096 1.075402
- Geolocation Orientational Variance RMS [degree] Omega 0.868 Phi 1.039 Kappa 2.454 (Geolocation RMS error of the orientation angles given by the difference between the initial and computed image orientation angles.)
- Image Coordinate System WGS84 (egm96)
- Output Coordinate System WGS 84 / UTM zone 10N (egm96)
- DSM and Orthomosaic Resolution 1 x GSD (1.86 [cm/pixel])
- Number of Generated Tiles 1 / Number of 3D Densified Points 9441467 / Average Density (per m 3) 437.92
A Point Cloud is the set of three-dimensional distributed points which result from a laser or photogrammetry scan. Each point cloud is calculated by matching several photographs (in the case of photogrammetry survey) so as it corresponds to a point of the surface of the surveyed object. The density of a point cloud is dependent on the quantity and quality of the photos taken, but also on the followed protocol of the shooting(7).
This point cloud still image above has five million points of the smallest resolution available, generating a ‘dense point cloud’ that can be 3D rotated in real time. Our internal followed protocols for all of our drone missions provide: safety, efficiency and proven results. Your second hint: the spillway is in the lower right of the point cloud image.
A Mesh Model is a surface that is constructed out of a set of polygons that are joined together by common edges. A polygon mesh is a collection of vertices, edges and faces that defines the shape of a polyhedral object in 3D computer graphics and solid modeling(8)
This is usually the final step. After the various consultants have poured over the shared copy of the point cloud, adjustments, additions and suggestions can be collaborated within the cloud. Our final contribution concludes with this ‘pretty picture’ used to tie in all the digital aspects of the project. Commonly this is the marketing showpiece and is often presented with an animated 3D fly-thru.
We welcome your comments and are happy to answer any questions you have on this sample photogrammetry workflow.
(6)Pix4D excerpts of quality control report for the Francis Dam, data processed via NewAgeProcessing on March 31, 2018
All images produced and copyrighted by NewAgeAerial.com – 2018
NAA response to the Moccasin dam emergency
March 2018, updated May 13 2018
2018: 2017 all over again.
Massive amounts of rain in a watershed causing evacuations downstream, what to do next time.
All of Northern California is acutely aware of water. Recent history dictates there is not enough of this liquid gold as we continue to endure a decade long drought. Add in a pineapple express and/or the ‘March Miracle’ two years in a row and we end up with more water than systems can handle in a short period of time. Reasons for this? The experts will continue this debate in politics and think tanks for years to come as water is the lifeblood of California. Continue reading Moccasin dam response
Western Slope Sierra Nevada Pine Bark Beetle Workflow
As per the contract dated March 8, 2017 NewAgeAerial (NAA) has provided an aerial inspection carried out in compliance with all local, state, and federal laws. The inspection has taken place on State Highway 89 from Truckee, south 9.5 miles to approximately the Homewood turnoff. Deliverables from the aerial inspection included are: excel spreadsheet of all trees in question, detailed maps, image breakdowns and overall summaries of our findings with still photograph examples of outlined areas of interest. The process of singling out the trees in question as identified by our arborist in this report in the field is done with a mobile application. We use Avenza to import our RGB map onto both Apple and Android devices. With this mobile application you can navigate via the devices GPS to within 6 feet on average of the identified tree.
Rice Crop Stress Mapping
Our flight today took us out of Yuba City, Sutter Co. Airport O52 before 0800 on October 26, 2017. Flying at 1500AGL out of controlled airspace toward the city of Oroville, following the Thermalito forebay we flew four grids of various altitudes and directions shooting with a Canon 80D and various telephoto lenses in RAW 4K. On the return leg we flew downstream back to Marysville and Yuba City taking note of the levees and ongoing upgrades. This is a small sampling of some of the 500+ images shot in an that hour flight.
Morning flight out of Sutter County to document the continuing process of the February 2017 event at the Oroville dam. All images shot from the Piper Cherokee 6 at 2000’AGL and are property of NewAgeAerial.com and not to be used without permission. No UAVs where used in any of these images
As we continue to expand our knowledge base with California rice growers, we took some time to say ‘thanks’ with this short clip
noun: a large accumulated stock of goods or materials, especially one held in reserve for use at a time of shortage or other emergency.
Going back to pen and ink drafting 101 – this is a projection, with the new green digital point cloud projected above the stockpile. All green lines are real 3D data, spatially located.
- On the right side there is a ‘void’ where material is actively being withdrawn
- The surface is not a ‘mesa’ and flat, of course not – but some LIDAR equipment will not be able to pick up these variations from the ground
- There is some red on the left side – that actually indicates below ‘grade’. The soft purple color is ‘grade’ and is not counted toward the volume. Looking back to the original image you can also see where the water is puddling, again the lower elevations.
- There are some calculations in the left margin telling the user that this ‘huge’ pile(using a multiplier of 1.33) has a volume of 63,299.13 cubic yards.
- With this process it took less than 17 seconds to define the shape, input the density factor and generate the result, really 🙂
- This process is accurate to +/- 9% and can be used in a variety of ways as it is GeoLocked 3D data. Want to find and remove 38,000 cubic yards of material from this pile? Do you want to load it from the outside road or on the inside track? Draw a new polygon projection and experiment in real time to decide which would be the best solution for your crew.
This is a sample page of our FINAL report for the stockpiles for this location.
It has all the information you would expect to see:
- Material type
- Stockpile name
- Multiplier for cubic yards
- GeoLocked coordinates
- Volumes for cubic feet / yards / tons
So THIS HUGE number is 62,357.99 and the cool 3D projection above is 63,299.13 – a difference of 941.14. What gives? “Isn’t this all Geo something or other 3D pointy things data?”
Here is the backstory without getting ‘geeked up’.
The down and dirty quickly done green point cloud that was generated on the fly is ‘good’ at approximately 9% error. When you let our other applications process this same pile and generate the final report – it is +/- FIVE PERCENT.
That is HUGE
How accurate are your stockpiles? Do you have reserves? NewAgeAerial.com can be your 5% inventory asset. Contact us today and we can talk about your needs.
Without the Wiki ‘testament’ and boring history lesson, man moves dirt – lots of it, all the time.
Strap in because this whole industry has changed overnight, and it is only going to go faster and reach wider. NAA has the legacy behind us with soils, levees, geotech, RC, fixed wing airplanes and had more camera platforms to count.
Traditionally to get aerial photography it went something like this;
Find a pilot who has a Cessna 172, minimally you had some useful skills with your Minolta camera and your new 200mm zoom lens and you loaded up with Fuji film with some different ISOs. Open up your wallet, call ‘CONTACT’ and zoom off into hopefully blue skies on the only day you and pilot are in the same zip code, to take ’10s’ of images. Now when you got back down to terra firma and rushed your film canisters to Longs Drugs and in a short 10 days or so you would actually get a call on your rotary phone from a live human to ‘invite’ you to come to photo department to pick up your 5x7s and oh they ‘just happened ‘ to be having a sale on Kodak film. Rush right over and open wallet. Tear open the package on the counter careful not to spill or touch the negatives and leaf thru the 4 rolls of 36 exposure images looking for just ONE good shot from those 144 ‘attempts’.
Wing was in the way – nope
Strut was in the way – nope
Light flare bounce back – nope
Tons of blurry images – nope
with 138 images scattered all over the counter, you and your instant expert ‘friend’ on the other side of the counter marvel at the ONE shot that made it all worth it. After many ooohs and aaahs, you scoop up all the rejects, grab 4 more rolls of Fuji film at full price and head home knowing it was a good day because you don’t have to do it all over again, this time. The client will LOVE this aerial of their project and pay you extra to have it blown up to mount on the wall like a trophy with a nice little bronze tag embedded into the frame with the date.
Here is where the New Age part comes in.
Fast forward to April 21, 2016.
Arrive at client location 0830, sign in and gear up. Discuss safety briefing, define potential areas of concern and no fly zones.
0900: Discuss mission parameters for the day, main targets and secondary locations and angles needed for the best results.
0930: Preflight and safety check
0945-1230: Fly missions via computer with safety officer. All missions VLOS (visual line of sight) and flown under 200′
1300: Review raw images and videos on laptop in field. 950 stills taken and over 18mins of critical video retained.
1330: Packed up and on the road
48 hours later all 28 piles have volumetrics computed with a 3D interactive cloud based map that is shareable across the net to any web enabled device.
Enjoy some of these images of the New Age of aerial survey!