Skip the expensive RTK and PPK gear. Get it close. Then fix it.
A new way to get highly accurate aerial maps without the complexity or cost.
As of April 6, 2018 we have enabled our new Manual Georeferencing workflow for all jobs that still have active Advanced Outputs available (i.e. within the last 30 days). This new workflow utilizes surveyed Ground Control Points (GCPs) to increase the accuracy of data that has already been processed by Maps Made Easy.
The new adjustment process is far simpler than before and will allow for the fine tuned adjustment of data that has already been processed to be pretty close to the actual location. This process is meant to augment the accuracy of maps that have already been processed using geotags.
NOTE: This feature is currently free to use but it may eventually have a cost associated with it that is proportional to the size of the original job.
Manual Rereferencing turns this:
Into this (less than 1 cm of error):
This should probably come with an epilepsy warning...
1. Run a job using our 'Camera GPS' workflow that uses the image geotags to georeference.
2. Click the 'Adjust Alignment' button at the bottom of the 'Job' section of job's the Map Detail page.
3. Import a CSV file that contains the surveyed GCP data.
4. Adjust the location of the GCP markers to where they are supposed to be.
5. Click 'Realign Now' and the job will run as you are used to but without the upload step.
Use 5 to 8 GCPs that are spread out throughout the coverage area. More is OK but not always helpful. 3 GCPs is the bare minimum.
Once the job is processed a new map will be placed in your list of completed maps. The realigned map will show that there are 0 source images. Measurements, annotations, and sharing will all work the same.
The DEM and colorized elevation layer will be reprocessed according to the GCP data. Here you can see a comparison between an slightly tilted area and its flattened version done with GCPs.
Rereferenced maps can be added to Location Maps in the same way that normal ones can. Here is a sample of 2 visits to a park with lots of active construction around it. Try zooming way in on some features and hide the latest layer to see how close they line up. These maps are within 1 inch (1 inch/pixel data) over the entire 160 acre area (65 hectares).
Play with it full screen here:
3D related files (XYZ, LAS, OBJ, KMZ) are not reprocessed and are not provided.
The GCP File
The GCP file that gets imported needs to be a .CSV file that contains a header line and no spaces after the commas.
This is what it looks like in Excel:
This is what it looks like as text:
44.040066,-121.415358,20.14,Little Rock of 3
A sample file is available for download in the Step 1 section of the rereferencing page.
Adjusting the Markers
Once the file is imported properly, you will see the GCP locations that were contained in the file drawn at the locations that were defined.
The markers are where the GCP locations say they should be and will not likely line up with the processed imagery. Why would you be doing this otherwise?
The GCP location for this marker was supposed to be in the center of the stump.
Click on the marker and drag it to where it is supposed located to be at the time of your GCP survey.
The accuracy of the reprocessing will only be as good as the surveyed points and the marker placement will allow.
While all the markers are being adjusted you can see the offset for each point in the table:
Once everything looks good, hit the 'Realign Now' button.
So to do this now....we make a map the usual way but after processing we go back open it...add GCP and run the process again?
You run the GCP process after using the geotags to create the map. The manual and basemap workflows have been disabled. You should use your geotagged images to make your initial map and then use the GCP process to refine it.
Dumb question. Do the selected GCPs have to be visible both on the Google Maps (GM) basemap and the original Camera GPS map? If I'm mapping a construction project, which of course is too new to show on GM, choosing a feature recently built would not be correct. Right?
Nope. All you need is the coordinates and elevation. You can then drag the markers around to match up with the wherever the measurements were taken in the processed map.
alright, I'll give it a try. Thanks.
Would it be correct to refer to the number under OFFSET(m) as the accuracy, i.e. in your example above "submeter accuracy" ?
The offset is the distance between the initial reconstruction and the measured points. It will always be up to a few meters off since it relies solely on the GPS of the aircraft. Once the rereferencing is done it can easily be within 1 cm.
Thanks, Zane. I did my first Manual georeference job w/ 5 GCPs (white paint crosses). The straight map (without correction) is more accurate than after corrections. I used a TRIMBLE GEOXT for the coordinates. The map name is MARBLE MTN 5/18/18. At the top left corner you can see that AFTER corrections the roadway is a full width off. BEFORE corrections is only about a foot off.
Should I go back and get more CGPs?
Off of what though? It looks like the markers are now right on your Xs now. Your Trimble is more accurate than Google Maps and if the coordinates for the markers are where you measured them to be this map is looking good. The real check is to measure some locations and compare them against the processed map.
I see, I was "assuming" the GM was the end all be all, when in fact my Trimble readings are more likely to be correct. My clients understand I'm not offering survey-quality geomaps (not a surveyor) but with this feature I feel comfortable using the term submeter precision.
"The real check is to measure some locations and compare them against the processed map." Would this be collecting Trimble readings, then right clicking on the manually corrected geomap and checking the difference?
GM is certainly not the end all be all. It is better than others, which is why we recently switched over but I will give you $100 if you can find a spec for it anywhere on the web. They don't publish it.
Pick a few specific points on the map and right click on them to bring up the coordinates. Then go measure them. They will be VERY close. That is your measured error and it will likely be a centimeter or two if the input GCPs were good.
Sorry to be dense, Zane. You lost me here: "Pick a few specific points on the map and right click on them to bring up the coordinates. Then go measure them." Exactly how would I measure them?
In your rereferenced map, get the coordinates of a couple of locations by right clicking. Then take your Trimble unit out and take location measurements for those spots. They should be very similar. We usually like to verify things like the corner of a storm drain or existing feature on a roadway.
I understand that step, but how do I measure the measured error? How do I come up with an error of an inch or a centimeter. I'm not getting that step.
Take your coordinates from our map and calculate the distance from the coordinates of the measured location. That will be your error.
You can use this calculator:
Thanks Zane! My first attempt gave me a 129 CM error but that was quick and dirty, am sure I can refine this down. Appreciate the help!
Got em all down to 10CM.
I'm new on this site.
Please bear with me.
Can you confirm when referencing images:
Can I get a las (or other 3d) model after correcting the mission with my GCPS.?
Can the coordinate file format be in northings and eastings ?
Ross: As noted above, "3D related files (XYZ, LAS, OBJ, KMZ) are not reprocessed and are not provided."
All coordinates must be provided in decimal degrees as shown in the provided sample.
I've been trying to make the alignment but nothing seems to happen. It's like there's a button missing. I am able to select my CSV file (and I'm pretty sure it's in the correct format), but nothing comes up in step 2. I've tried a few different browsers to eliminate that. (Safari, Firefox, Chrome). Any hints? Thanks.
here's my map: https://www.mapsmadeeasy.com/maps/detail/894cfcf34ca74ef3b05eda532b60f804
There are some very visible fence corners and a very visible old rusty tank that appear in both the drone photo map and in Google Earth. I only want my map to fit onto the Google Earth map. How can I slide my map to suit and fit Google Earth? For the purpose of making the map suitable for visualization purposes only. I don't want to go to the trouble of setting GCP's for this. Thank You
Just tried this out on a map the standard DJI workflow "tilted". Worked very well. Two suggestions in the spirit of beta feedback:
1. Raise an error before processing if user (accidentally) has specified no valid GCPs. In my first attempt, I somehow switched LAT and LON, so had all my GCPs outside the ROI. I should have twigged since I had no markers to drag around on the map, but I didn't pay attention, since I was happy with the x,y and just wanted to clamp the elevation right. But MME cheerfully went and calculated for an hour, and then came back with a ~800kb empty TIFF. My mistake, but something failed inelegantly in processing an empty set's worth of GCPs to generate the empty TIFF.
2. In the table generated as you move GCPs around, you show each GCP's delta (x,y)-distance. Could you also show the delta-elevation, either "raw" (specified ELEV - current z) or rebased in some way so e.g. the delta z is 0 for the 1st GCP? The latter is so a simple translation to a different reference elevation (absolute vs relative, or different truth DEM vs the one you look up) would not generate high delta z for all GCPs, only a tilt/deformation would. The goal of all of this is to indicate the amount of deformation being corrected during data entry, and thus alert user if a specific GCP is bad. For instance this got me when I wanted to get the top of a cliff but instead got its bottom (more accurately, my "truth" DEM erroneously did), and the spurious delta Z of 5m in the MME map transformation made a nearby lake tilt. Fixable when I re-examined each GCP to debug, of course, but this would have found it sooner, more elegantly.
I processed a map with survey located ground control points. When I insert the geotiff file into the survey file (autocad) the aerial is shifted approximately 4 ft to the southwest. Is this the level of accuracy I should expect or is there a more logical explanation? My survey is based in in Florida State Plane Coordinates (FL83-EF - NAD83 Florida State Planes, East Zone, US Foot)
Everything we do, input and output, is in WGS84 EPSG:4326 decimal degrees in Latitude and Longitude. GCP coordinates should be supplied in this way. Any projections of the outputs to other coordinate systems is up to the user.
Do you have any advice for an entry-level means to capture the GCPs?
I was looking at Luis's Trimble GEOXT. Assume it's the 3000 as 2008 was superseded.
Assume you need a GPS receiver suitable for GIS-based tasks in the first place otherwise how would you capture the data?
Trying to get a handle on the workflow is all part of the process.
The other people on this thread will likely have more to say on this topic than we will.
Anthony Nixon, if you need to achieve survey grade accuracy (cm level) you should measure your GCPs with base and rover GNSS receivers. Also, If you need absolute vs. relative accuracy, then your base will need to be setup over a known point (unless you can use CORS or Ntrip service as your base). Someone else above inquired about overlaying and aligning their map output to google sat image rather than accurately georeferenceing. I do this quite a bit for visual displaying only, it’s easily done with the georeferencer tool in QGIS. If you are GIS capable, just google search the process, there’s good ‘how to’ documentation and video available.
I'm trying to adjust elevations on my map to correspond to a survey with accurate elevations and despite adding uploading a .csv file with five GCP details (I'll add more once I get the principle working!), which looks the same as the sample, I don't get the option in Step 2? I see just one single marker on my map, which I can move and the lat/long changes, but no other information is shown and the realign button isn't available. What am I missing?
Douglas MATTESON: If you use QGIS, you can align your aerial orthoimage to Google Sat in Q with the 'Georeferencer Tool'. There are a few 'how-to' videos on Youtube and other general help blogs also, its not difficult at all. If fact, I think they may even be a 'Q-georeferncer' tutorial somewhere on this form.
Thanks Chris Campagnaro, but I wanted to regenerate the MME map and I am pleased to say that Tudor spotted an error in the uploaded .csv file, where one of the longitude coordinates had a rogue space added from the copy/paste I had done. So, I removed the character, Step 2 then worked and the map has been reprocessed and includes the revised elevations I needed.