If you have not come to this page from the sequence starting at Starting a New Cave" then go and read that first.
This page follows directly on from creating a new cave. If you haven't read thos pages, please go back and do so.
exactly analogously to creating a new cave.
As with a cave, you will find the process a lot easier to follow if you Edit an existing entrance first.
New in 2021 are fields for the latitude and logitude (WGS84 - the same as your GPS displays). Unless someone has already created the *fix point for the cave, these should be entered in the form. IF the *fix has been done, then leave the WGS84 fields blank.
We always write degrees with decimals for fractions of a degree, e.g. 42.357 (not 42 degrees 21 minutes 25 seconds, or 42 degrees 21.42 minutes).
These WGS84 fields exist for newly-discovered cave entrances for which we currently have no location information except for a GPS reading by the original discoverer. These discoveries have a habit of getting completely lost: so enter it so that someone can find it again to properly survey it. In due course the cave will be linked in to the survex survey system using *fix statements. If this *fix work has been done, then that is authoritative and you do not need to enter location information on this form.
When a nerd creates a *fix statement, in the right place, the nerd will manually delete the WGS84 values on the Entrance.
The survex location uses a *fix statement and it looks like this:
*cs LONG-LAT
*fix p2023-js-02 reference 13.80841 47.69055 1745
*entrance p2023-js-02
If you are doing this for the first time, it might be a good idea to put it in the same survex file temporarily. A nerd will move it to the right place later.
For the 1623 area it is easy. Each year has a different file. For 2019 there is a file gps/gps19.svx which contians all the *fix statements for new locations that year.
For the 1626 area it has got horribly complicated and you should talk to Wookey and Becka. Most likely it will have to go into fixedpts/1626-no-schoenberg-hs-not-tied-to-caves.svx
And in your main survex file you will need to make the connection between the survey points in the cave and the external location. This would be something like this (not real data), where survey station "1" is the tag at the entrance of the cave, and outside the begin/end section it is called "2023-js-02.1"
*equate p2023-js-02 2023-js-02.1
*begin 2023-js-01
*export 1
...
*data normal from to length bearing gradient ignoreall
1 2 4.46 099.3 -54
...
*end 2023-js-01
There is a lot more to say about how to record the best GPS data, and how to link GPS with survey points, e.g. see Getting a GPS fix
The altitude is not nearly as vital as the lat/long numbers. GPS altitudes are still pretty bad, and even the new Galileo system won't promise anything better than ± 0.4m in 2030. (If you take the altitude from a track while moving the altitude can easily be 15m wrong.)
In practice, for us on the plateau, we get repeat measurements of the same spot by different teams in different years to be accurate to only about 3m. This is fine for finding entrances, and for checking whether two different teams have found the same cave, but it is not adequate for loop-closure. That requires particular care with averaging the reading over 2 minutes, and use of a location with good view of the sky, away from vertical rock, and surface survey using instruments to get from the GPS point to the actual cave entrances. To get a decent altitude measurement requires averaging over 10 minutes, and it is still not good.
In previous decades the location of an entrance was the output of a whole lot of surveying and position fixing (e.g. see laser points). Today, an initial location of an entrance is available by GPS at the beginning of the process. So we have these fields to record the data. [We don't yet have the code to automatically add the *fix statements into the fixedpts data, or to the essentials.gpx download to be used for prospecting though.]
The full list of fields is documented: the full list of data-entry fields when creating an entrance.
Back to the previous page in this sequence New rigging guide.
A side trip to see how to do this as a file upload process using git, the cave description data file
Now go the the next page in this sequence Write the full cave descriptions with diagrams.