Missing altitude is not zero
02A missing height, an explicit zero and a positive height convey different information.
The public example geo:48.2010,16.3695,183 supplies 183 meters in WGS-84. Compare a height to its reference, not to an assumed floor or terrain height.
Source for this drawing: RFC 5870 · Read RFC section 3.4.2 ↗
New to this? Start hereA quick picture + helpful background
A message needs an address.
Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
- Altitude
- The optional third coordinate: height in meters in WGS-84, not a floor number or an implied height above local ground.
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
Never fill an unknown altitude with zero.
- If altitude is unknown, the altitude component and preceding comma MUST NOT be present. Unknown altitude MUST NOT be represented by 0 or another arbitrary value.
- When present, altitude MUST be in meters in WGS-84. Zero MUST NOT be mistaken for ground elevation; local terrain may be above or below the reference level.
- With missing altitude a consumer MAY assume the physical surface at the latitude and longitude. This interpretation does not make the URI equal to one containing an altitude.
The diagram is an illustrative vertical section, not real Vienna terrain. It uses the RFC’s wording “WGS-84 reference geoid” (§3.4.5); it does not teach that WGS-84 height is a measured local ground elevation. The 183 m value is the public §6.1 example.
Read the RFC section ↗