Altitude Discrepancy Issue

CesiumJS
1

ALTITUDE DISCREPANCY ISSUE

1. Notice the Altitude at the head of runway 08 at Burbank airport is 727 feet MSL.

http://155.178.201.160/d-tpp/1510/00067AD.PDF

2. When I add a marker at 727 feet, it floats a little over 100 feet above the runway. http://paperdrone.com/devq/727_feet_elevation.png Notice the Altitude in Feet form field.

3. But to place the cursor at ground level in Cesium, I have to put it at 620 feet to appear 2 feet above the numbers, (08). http://paperdrone.com/devq/620_feet_elevation.png Notice the Altitude in Feet form field. That's a 107 feet off.

The reason I bring this up, is because if using Google Earth, the ground level as illustrated is pretty close to the actual ground level and I'm trying to to get my Cesium planner to appear as when interacting with the ground plans for landing precision. http://paperdrone.com/devq/GE_at_KBUR_727ft.png

My previous developer is off the project for the time being and I'm trying to make sense of it myself during the lapse. I was told that Cesium's height is above the ellipsoid, while Google Earth's is above mean sea level. BUT... practically, I'm not sure how to account for the offset to fix this.

Appreciate the help in advance
j.

2

Hi,
The discrepancy you see is the difference between mean sea level and the WGS84 ellipsoid. You will need to convert your altitude from MSL to Ellipsoid height. We use the EGM96 model, which encodes a grid of height offsets from the WGS84 ellipsoid to define a shape that approximates mean sea level. After plugging in the latitude and longitude from your screenshot, I see the difference between MSL and the ellipsoid is -34.444m (113 ft).

There’s a handy online calculator you can use to verify yourself if you’d like:

http://www.unavco.org/software/geodetic-utilities/geoid-height-calculator/geoid-height-calculator.html

Alex