FMV measurements

[FaroukRohoman]

I created a FMV using a Virb Elite and # can display the video and frame outlines, points etc. without a problem.  All the data is in WGS84; however when I measure a distance on the video it is way off.  What should be ~3.5 metres shows as 50 metres.  I am using the ESRI open streets as the base map.

Where should I start looking.  full-motion video (fmv)@

Farouk Rohoman

[CodyBenkelman]

Farouk 

Can you confirm that you are measuring XY features on the ground?   Vertical measurements aren't supported yet in FMV, so if you're attempting to measure the height of an object in the video, you'll actually be getting a measurement of that object projected onto the earth...

If that does not answer the problem, can you describe a bit more?  Does the video footprint appear to be the correct size?  Are your videos captured at an oblique angle or a nadir view?  Also, what version of ArcGIS are you using, and are you working at an extreme north or south latitude?  

Cody B

[FaroukRohoman]

Hello Cody:

Thanks for the quick response.  Working around Niagara Falls Canada. The video footprint seems to be the correct size.  The Virb is mounted on a bike and the pitch angle recorded averages 30 degrees down.  I tried measuring the width of the bike path "on the ground" which should be ~3 metres and got ~50 metres.  I suspect that the distortion is occurring because the image is oblique and not nadir.  The following is a couple of lines from the csv file from the camera

microTime,latitude,longitude,altitude,heading,pitch,roll,horizFOV,vertFOV,relAzimuth,relElev,relRoll
1500642104000000,43.40325,-79.81407,149,132.0414,-33.13308,0.9303337,115.4,70.3,0,0,0
1500642105000000,43.40324,-79.81407,149,132.7302,-33.34009,8.095687,115.4,70.3,0,0,0

Farouk Rohoman

[CodyBenkelman]

Sorry, I should have thought of this.  The altitude values passed into the multiplexer have to be adjusted to represent height above ground - your altitude values represent height above sea level. 

If you have relatively flat terrain, you can simply enter the ground elevation into the multiplexer.  If your terrain varies and you want accurate measurements everywhere, you'll need to adjust each altitude value (using a DEM such as from ArcGIS Online World Terrain) so each sample is height above ground.

from the user doc at http://esriurl.com/FMV132Manual

SensorAltitude: Although the MISB specification defines sensor altitude as the altitude of the sensor Above Mean Sea Level (AMSL – also known as orthometric height), the current version of the multiplexer does not allow input of a Digital Elevation Model (DEM), so adjustment for variable height above ground are not supported. As a result, input of SensorAltitude into the multiplexer must represent height above ground in meters. See below for alternative workflows for calculating these values.

Please review section 5.2.2 in detail 

[FaroukRohoman]

Thanks Cody:

This makes sense.  I will try adjusting to agl

Farouk Rohoman