Update README.md

README.md

@@ -190,11 +190,11 @@ Transport of GNSS coordinates. Altitude and DOP are optionnal.
 
 |    1B    |     4B      |     4B      |    0/4B    | 0/4B  |
 |----------|-------------|-------------|------------|-------|
-| `header` | `latitude` | `longitude` | `altitude` | `dop` |
+| `header` | `latitude`  | `longitude` | `altitude` | `dop` |
 
-The `latitude` field is a C-type float and is mandatory.
+The `latitude` field is a C-type float and is mandatory if the `valid_gnss_position` flag is set
 
-The `longitude` field is a C-type float and is mandatory
+The `longitude` field is a C-type float and is mandatory if the `valid_gnss_position` flag is set
 
 The `altitude` field is a C-type float and its presence is annouced in the `header`
 
@@ -202,14 +202,16 @@ The `dop` field is a C-type float and its presence is annouced in the `header`
 
 ##### Header
 
-|           1b             |         1b          |    6b    |
-|--------------------------|---------------------|----------|
-| `altitude_presence_flag` | `dop_presence_flag` | reserved |
+|           1b             |         1b          |           1b          |    6b    |
+|--------------------------|---------------------|-----------------------|----------|
+| `altitude_presence_flag` | `dop_presence_flag` | `valid_gnss_position` | reserved |
 
 The `altitude_presence_flag` must be set to 1 if the `altitude` field is present in the packet.
 
 The `dop_presence_flag` must be set to 1 if the `dop` field is present in the packet.
 
+The `valid_gnss_position` must be set to 1 if the `latitude` and `longitude` fields are present in the packet.
+
 #### Type 2 : Locally referenced localisation
 
 Transport of locally referenced 2D or 3D localisation. The "repère" is identified by an UID.