Convert meters to feet prior to processing?

[RockRunEnterprises]

Is there any way to convert Z data of images prior to processing? My camera (DJI X5) only captures the data in meters which in turn Drone2Map views as feet. Everything I do in ArcGIS is in feet, typically State Plane.

I suppose this is a silly question, but all of the products D2M creates are unusable to me as far as real life elevation data is concerned.

A simple Z converter would be a great feature to have in D2M under the "Image Properties" section.

[DanPatterson_Retired]

The owner of the group is jschuyler-esristaff I have flagged him.  Perhaps you can be directed to a fuller help file, than I could find.

[AaronWoods]

I'm a little confused by the question.  The Images from a drone don't have any unit a measure, they exist in Image space, not coordinate space.  The only Z value I can think of for the drone Images (when taken from the SD card) is the "Altitude" taken from, which is really just height above takeoff location as opposed to a real elvation/altitude (MSL).  The images are Geotagged by the Drone, but that is simply a point location from which the image was captured.  When the images are processed by Drone2Map (which is essentially Pix4D) the software uses the camera specification/metrics  and builds a 3D Pointcloud from automatically generated keypoints that are identified in multiple images.  If you are not applying/using any ground control points, your Z measurements will be off (when compared to local Topo maps/data, however the relative heights of objects will be correct within the scene).  I think you may just have issues with reprojecting the data generated by Drone2Map.  If I recall, the default output is UTM (which is Meters) but can be reprojected into State Plane or other Feet based coordinate system

[RockRunEnterprises]

I've taken photos on the ground to spot check elevations and I'm getting height values assigned. Doing a conversion from meters to feet, I'm coming up around 19% under from true elevation above sea level. I'm starting to think it's some kind of error in the camera. Horizontal accuracy is near perfect though. Like you said, the DSM Drone2Map creates is still relatively correct, but not globally.

[AaronWoods]

A GPS doesn't collect Z information in relation to MSL (mean sea level), but for a theoretical Elipsoid, and to be honest, I don't think the DJI drones even get height from the GPS, but from barometric readings estimating height above takeoff. I'm afraid a detailed explanation of MSL heights, vs elipsoidal and the resulting Geoid seperation is beyond me personally (there is a entire scientific area known as Geodesy that just studies this kind of thing) but ESRI has somehelpful information about this, http://www.esri.com/news/arcuser/0703/geoid1of3.html.

In a nutshell, if you require accurate heights, you will need to establish some Ground Control points (GCPs) that are differentially corrected to NGS benchmarks. Here is another link to NGS/NOAA presentation. http://www.ngs.noaa.gov/GEOID/PRESENTATIONS/2007_02_24_CCPS/Roman_A_PLSC2007notes.pdf

Sent from my iPad

[RockRunEnterprises]

Thanks Aaron. I need to do some more research about GCPs. I did try using GCPs from the basemap in D2M to no avail. I must be doing something wrong still.

[RockRunEnterprises]

As an update to the original question, I am producing accurate DSM files that are using GCPs in meters. However these rasters are not usable to me in a global scene without being converted to feet. Short of having higher level licensing privileges, I have to create contours in 3D analyst(create TIN, convert TIN to Raster) and do a conversion to feet with this process. It's just a little cumbersome.

I would still love it to have the feature built in to D2M as a way to convert to your working coordinate system within the processing functionality.

I'm all ears as to a better way forward.

[DouglasRidenour]

Patrick - The Drone2Map 1.1 update likely solves your elevation unit issue. Aaron is right on target that you need to use Ground Control Points if you want greater accuracy in the solution. However, the answer to your original question is that you can batch edit the exif metadata in your collected images using the freeware ExifTool by Phil Harvey. It is a command line tool but it can rapidly change the metadata values. As as always don't change your source data but work on a copy of it so you can easily revert.