* NOTE: This message has been edited. To see the new additions, look/search for the text "[ADDED]". *
***********************************************************************************
Regarding: New Celestia feature -- Locations
If you are interested in (or already are) creating a Celestia Location file, please read this message. Sorry that it's a long one, but it contains a lot of information gathered from many other messages/topics in the forums.
What is a Location file?
Starting with version 1.3.1 pre6, Celestia allows text labeling of "Locations" on planets and moons. Basically, a Location file tells Celestia on what object and where to display Location labels, by using Longitude and Latitude coordinates. The following is an example entry in a Location file:
Code: Select all
Location "Seattle" "Sol/Earth"
{ LongLat [ -122 47.5 0 ]
Size 10
Importance 100
Type "City" }
Size and Importance Values
From Chris Laurel:
Size is the diameter of the location and is used to determine how close to the location the camera needs to be before a label should be rendered. Importance can be used to override size for small locations that you still want visible from a distance, like a lunar landing/crash site.
[ADDED Aug 1, 2003]
Altitude Value
Altitude is specified as the third number value in the LongLat Parameter.
From Chris Laurel:
Altitude is the distance of the location above an object's surface. There are occasions when you might want to label a location that's above the surface of a planet. For example, you could place locations to mark the various rings and gaps in Saturn's rings.
[/ADDED]
It's my opinion that the Celestia Development Team, along with the current Location file creators, need to "get together" and define a list of Size and Importance values for specific objects, so that anyone who creates a Location file can use this pre-defined list of values to make their Location file consistent (Size & Importance) with everyone elses Location files.
Why would we want to do this? So that when a Location file has a few thousand entries in it, or the user has many Location files of different things (cities, mountains, bodies of water, landing sites, whatever), the user can better control what labels actually get displayed.
From Chris Laurel:
Yes . . . some sort of guidelines need to be established. For planets other than Earth, importance can be omitted so that it defaults to the size. The only exceptions I can think of are spacecraft landing sites, which I think are worth giving high importance.
On Earth, there are more judgement calls involved . . . What importance should be assigned to a city of one million people? A capital city? The VLA radio telescopes?
There definately needs to be some discussion about this BEFORE there are 100 different Location files out there, all with different Size and Location values that will clash with other files.
For an example of why this needs to be done ... using Fridger's Earth Locations file (http://www.shatters.net/~t00fri/earth.ssc.zip), go to Hawaii, and turn Location labels on (& key). You will see that every single Location label on the Big Island is stacked on top of one another, with no way to manipulate the display to see them all (rotate, orbit, set Size value in dialog, etc.). It's just a big green blob <frown>. And yes, every location is properly specified and valid.
By looking at this file, you will see that every location at these coordinates has the same exact Size and Importance values. BUT, even when they don't, the labels are still displayed on top of one another as you move closer to the surface. So, Celestia needs to provide a way to display multiple labels that are defined at the same, or very close, coordinates in a list-like fashion. (I also posted a message in the Bugs forum regarding this "stacking" of text labels: http://ennui.shatters.net/forum/viewtopic.php?t=2954.
By pre-defining a list of Size and Importance values for Location file creators to follow, all Location files, created by anyone, will be displayed the way the user wants to see them via one set of end-user controls (the Locations dialog box).
Here is Chris Laurel's explanation of how the "Size" slider works in the new Locations dialog box:
Internally, Importance overrides Size when specified in a location definition. I suppose it's misleading to label the slider 'Size' . . . Instead, it should probably just be labeled show less and show more at either end. In any case, it's intentional that the user never sees Importance mentioned explicitly. It's just a device for .ssc creators to make physically small but very significant locations that can be seen from a good distance away.
Below is an example (ONLY an example) of some locations the list we create might contain ...
* Denotes an object that is currently recognized by Celestia 1.3.1 pre-release 6.
- Denotes an object that is not recognized, but could be defined simply by using a specific Size value:
Code: Select all
Object Size Importance Example
------------------------------ ------ ---------- -----------------------------
* Observatory ................ 100 Kitt Observatory
* Landing Sites .............. 200 Apollo missions to moon
* Crater ..................... 300 Take your pick
* USGS Surface Features ...... ? (see list at bottom of msg.)
* Other ...................... ?
Personally, I think Chris & team should consider changing "Seas" to "Bodies of Water", which would then include Seas, as well as the following additional types of water bodies. I would also choose to give Oceans the highest Size and Importance since they are the largest objects (at least on Earth):
Object Size Importance Example
------------------------------ ------ ---------- -----------------------------
- Bodies of Water
- Rivers ................... 500 Nile River
- Deltas ................... 1000 Mississippi Delta
- Lakes .................... 2000 Lake Geneva
* Seas ..................... 10000 Red Sea
- Oceans ................... 30000 Highest Pacific Ocean
There may be some good reasons, but why give Mountains, Valleys and Cities their own object classification? Why not have them as sub-categories under "Land Mass", like the following list shows. I would choose to give Continents the second highest Size and Importance values since they are second in size only to Oceans (at least on Earth):
Object Size Importance Example
------------------------------ ------ ---------- -----------------------------
* Land Mass (Continent) ...... 20000 NextHighest North America
* Mountain ................. 9000 Rocky Mountains
- Range .................. Wasach
- Peak ................... Pike's Peak
* Valley ................... 8000 Grand Canyon
- Country .................. 7000 United States of America
- National Forest Land ... Rocky Mtn. National Forest
- National Park .......... Yellowstone
- Gov't Headquarters ..... Washington, D.C.
- State/Region/etc. ........ 6000 Colorado
- State Capital .......... Denver
- State Attractions ...... Aspen (skiing)
* City
- Large .................. 5000 Population ? to ? (NewYorkCity)
- Medium ................. 4000 Population ? to ? (Denver)
- Small .................. 3000 Population ? to ?
- Town ................... 900 Population ? to ?
- Airports (?) ............. Denver International
- Amusement/Theme Park (?).. Disneyland, etc.
etc.
What's the First Step?
It would seem that the first step would be to figure out who will be in charge of this "meeting of the minds" (one of the developers?) so that all of us can submit to that person, our list of objects (items) to be added to the list. The list of location objects will then be compiled and updated / posted / e-mailed to all group members for comments. It doesn't have to be like a Webster's Dictionary, but should include basic items to be labeled on a planet or moon. Should it also include items in orbit, asteroids, deep space objects, etc.?
Once the initial list of items is finalized (agreed upon), each location item on the list will need to be assigned values for Size and Importance.
How to Use a Location File
In order to use a Location file, you must be using Celestia version 1.3.1 pre6 or higher, which can be downloaded from http://63.224.48.65/celestia/files/.
Then ...
1. Download the Location file(s) you want (see below).
2. Move the Location .ssc file(s) into Celestia's "extras" directory.
3. Run Celestia and goto the object (planet, moon, etc.) you downloaded the Location file for.
4. Turn on Location labels with the "&" key (On/Off toggle).
5. Move close enough to the object to see the Location labels.
Existing Location Files (as of July 27, 2003)
By Chris:
* Location files for Eros, Jupiter Moons, Mars, Mercury, Moon, Neptune Moons, Saturn Moons, Uranus Moons, and Venus: http://www.shatters.net/~claurel/celestia/files/locations/
By Fridger:
* 500 precise locations on Earth: http://www.shatters.net/~t00fri/earth.ssc.zip
* LARGE file, converted from UN ECE data: http://www.shatters.net/~t00fri/earth-UNECE.ssc.zip
By Darkmiss (Paul Roberts):
* Work-in-progress, major Earth citys (no observatorys or telescopes): http://www.bt.homepage.btinternet.co.uk/Files/Earth-Citys.ssc
[ADDED July 31, 2003]
If you use multiple Location files, and find that several labels overlap on a given location, please remember that this is a brand new, pre-release Celestia function and these files are currently on the "bleeding edge", so please don't get too upset <smile>. Some changes may be on the way that will help this, but for now you can do the following things yourself ...
If you find a location that is trying to display multiple labels get the Longitude and Latitude for that location (use Navigation/Go To... dialog) and then use a text editor to search one or more of the Location files for that specific location (Longitude and/or Latitude). There may be several to find, so make sure you search the entire file making a note of the object names.
Then, go back through the file and change one or more of the following until it gives you satisfactory results:
* Size
* Importance
* Longitude (small changes)
* Latitude (small changes)
Size and Importance are used by Celestia to determine at what altitude to show the label. So, you could change either Size or Importance for all identical entries, except for the most important one, to be a very small number. This will allow the important one to be displayed first (highest altitude).
[/ADDED]
.
.
For those folks who are interested in creating their own Location files...
Creating a Location File
The filename format for a Celestia Location file is <filename>.ssc, where <filename> is any filename you define.
Here is the correct syntax to define a Location of Type=City, from Chris:
Code: Select all
Location "Seattle" "Sol/Earth"
{
LongLat [ -122 47.5 0 ]
Size 10
Importance 100
Type "City"
}From Chris Laurel:
Size is the diameter of the location and is used to determine how close to the location the camera needs to be before a label should be rendered. Importance can be used to override size for small locations that you still want visible from a distance, like a lunar landing/crash site.
[ADDED Aug 1, 2003]
Altitude Value
Altitude is specified as the third number value in the LongLat Parameter.
From Chris Laurel:
Altitude is the distance of the location above an object's surface. There are occasions when you might want to label a location that's above the surface of a planet. For example, you could place locations to mark the various rings and gaps in Saturn's rings.
[/ADDED]
According to Chris, the current pre-release (1.3.1 6 or 7) includes recognition of the following 2-letter values for the Type entry, listed in alphabetical code order:
Code: Select all
Type USGS Definition
---- ----------------------------------------------------------------------------
AA Crater, craters A circular depression
AS Astrum, astra Radial-patterned features on VENUS
CA Catena, catenae Chain of craters
CH Chaos, Distinctive area of broken terrain
CM Chasma, chasmata A deep, elongated, steep-sided depression
CR Corona, coronae Ovoid-shaped feature
DO Dorsum, dorsa Ridge
FE Flexus, A very low curvilinear ridge with a scalloped pattern
FL Fluctus, Flow terrain
FO Fossa, fossae Long, narrow, shallow depression
FR Farrum, farra Pancake-like structure, or a row of such structures
LF LandingSite, Lunar features at or near APOLLO LANDING SITES
LI Linea, lineae A dark or bright elongate marking, may be curved or straight
ME Mare, maria "Sea"; large circular plain (MOON only)
MN Mensa, mensae A flat-topped prominence with cliff-like edges
MO Mons, montes Mountain
PE Patera, paterae An irregular crater, or complex one with scalloped edges
PL Planitia, planitiae Low plain
PM Planum, plana Plateau or high plain
RE Regio, regiones A large area marked by reflectivity or color distinctions
from adjacent areas, or a broad geographic region
RI Rima, rimae Fissure (MOON only)
RT Reticulum, reticula reticular (netlike) pattern on VENUS
RU Rupes, Scarp
TA Terra, terrae Extensive land mass
TE Tessera, tesserae Tile-like, polygonal terrain
UN Undae, Dunes
VA Vallis, valles Valley
Additional Celestia Types
-------------------------
XX = Other
City
Observatory
Currently listed by the USGS but missing from Celestia
------------------------------------------------------
AL Albedo Feature Geographic area distinguished by amount of reflected light
CB Cavus, cavi Hollows, irregular steep-sided depressions usually in arrays
or clusters
CO Colles Small hills or knobs
ER Eruptive center Active volcanic centers on IO
FA Facula, faculae Bright spot
LA Labes Landslide
LB Labyrinthus, labyrinthi Complex of intersecting valleys
LC Lacus "Lake"; small plain (MOON ONLY)
LE Lenticula, lenticulae Small dark spots on EUROPA
LG Large ringed feature Cryptic ringed features
MA Macula, maculae Dark spot, may be irregular
OC Oceanus A very large dark area on the moon (MOON ONLY)
PA Palus, paludes "Swamp"; small plain (MOON ONLY)
PR Promontorium, promontoria "Cape"; headland promontoria (MOON ONLY)
PU Plume
SC Scopulus, scopuli Lobate or irregular scarp
SI Sinus "Bay"; small plain
SU Sulcus, sulci Subparallel furrows and ridges
TH Tholus, tholi Small domical mountain or hill
VS Vastitas, vastitates Extensive plain
From Chris Laurel:
The two letter codes are the ones used by the USGS. I also permit "Crater" instead of writing "AA"--I'll introduce similar aliases for the rest of the feature types. You would add a city like this:
Code: Select all
Location "Wellington" "Sol/Earth"
{
LongLat [ 174.823 -41.275 0 ]
Size 10
Importance 500
Type "City"
}