Date: Wed, 21 Jul 1999 16:32:59 -1000 (HST) From: Claude Roddier To: SHOWALTER@ringside.arc.nasa.gov Mark, I followed your recommendation and here are my comments on the disks. I am leaving tomorrow and I am not sure that I'll be able to read my e-mail until end of August. I am going to a small French village and until recently there was no access to the internet! Best regards Claude ************************ Comments on the data set: My comments are very positive in the sense that I have been able without difficulty to understand the whole organisation of the data set and look at the files and labels. It seems to me that if I wanted now to use these data I could do it. There are only two points I'd like to comment. The first one is in the display of the GIF files in the subdirectories "browse". The images of PC1 have been rescaled and rotated to show the whole image of Saturn when the image has been taken on PC1 and WF4. This is a good idea but this should be explained in the tutorial in the fourth paragraph (4. HST/WFPC2 Images and Filters). If you have never seen the images, it is difficult to realize why the PC1 images are so small whereas the pixel size is twice smaller than the pixel size of the WF. My second remark is more important. I think an easy index to the files is missing. There is an index for each disk and an index for the whole set in the subdirectories "index", but they are quite impossible to read. If you display them on the screen of your computer you have to make an enormous window, and even like this each image is described in several lines on the screen. I would call this index the "formal" index and I think it has to be there. But I am sure potential users would find useful another index which gives only the most useful information, so that it is much smaller and easier to read. In the headers the main part of the information has already been given many times, and after a while you don't even look at it, but since it is there, it hides the particular information which has to be given just for the image described. I have tried to write down such an index with the information taken in the headers. I think this index should be in the "browse" directories for each of these directories and a general one somewhere on the disks. I did it for the cd 5 but in fact I realised it was missing when I looked at the images of the cd3 which are the images of the August ring plane crossing. Since I had reduced these data, I had my own notes and images and I compared them to the gif files of RPX_0003/199508XX/U2TFXXXX which are the images of the proposal 5836 by Nicholson. I was unable to find some of the files that you (Mark Showalter) had sent to me. When I looked carefully, I found that these images had been taken in the proposal 6216 by Trauger. So I had to go to another directory and look at the labels. If I had not known that these images were in fact taken at the same time as the Nicholson images I am not sure I would have found them. I wrote the "easy index" for the CD 5 that I did not know. Here is an attempt of what I think would be useful: RPX_0005 199511XX/U2OOXXXX/BROWSE TRAUGER 1995-11-20 0401 ,"U2OO0401T.GIF","SATURN " START_TIME = 1995-11-20T07:11:17 STOP_TIME = 1995-11-20T07:32:57 FILTER_NAME = F300W EXPOSURE_DURATION = 1300.00 Aperture type: WF2-FIX NO APPARENT PROBLEMS . . . 199511XX/U2TFXXXX/BROWSE NICHOLSON 1995-11-21 0301 ,"U2TF0301T.GIF","SATURN " START_TIME = 1995-11-21T10:40:17 STOP_TIME = 1995-11-21T10:45:17 FILTER_NAME = FQCH4P15 EXPOSURE_DURATION = 300.00 HST Target name: SATURN-EAST-ANSA Aperture type: PC1-FIX (PC1-WF4) MUCH OF SATURN 0302 ,""U2TF0302T.GIF","SATURN " START_TIME = 1995-11-21T10:48:17 STOP_TIME = 1995-11-21T10:53:17 FILTER_NAME = FQCH4P15 EXPOSURE_DURATION = 300.00 HST Target name: SATURN-EAST-ANSA Aperture type: PC1-FIX (PC1-WF4) MUCH OF SATURN 0303 ,"U2TF0303T.GIF","SATURN " START_TIME = 1995-11-21T11:00:17 STOP_TIME = 1995-11-21T11:06:07 FILTER_NAME = FQCH4P15 EXPOSURE_DURATION = 350.00 HST Target name: SATURN-WEST-ANSA Aperture type: PC1-FIX (PC1) MUCH OF SATURN THERE WAS ONE 4 SECOND RECENTERING 0304 ,"U2TF0304T.GIF","SATURN " START_TIME = 1995-11-21T11:09:17 STOP_TIME = 1995-11-21T11:15:07 FILTER_NAME = FQCH4P15 EXPOSURE_DURATION = 350.00 HST Target name: SATURN-WEST-ANSA Aperture type: PC1-FIX (PC1) MUCH OF SATURN 0305 ,"U2TF0305T.GIF","SATURN " START_TIME = 1995-11-21T12:07:17 STOP_TIME = 1995-11-21T12:15:37 FILTER_NAME = FQCH4P15 EXPOSURE_DURATION = 500.00 HST Target name: SATURN-EAST-ANSA Aperture type: PC1-FIX (PC1-WF4) Data quality: UNKNOWN MUCH OF SATURN BAD TELEMETRY FOR FIRST 150 SECONDS OF EXPOSURE 0306 ,"U2TF0306T.GIF","SATURN " START_TIME = 1995-11-21T12:18:17 STOP_TIME = 1995-11-21T12:26:37 FILTER_NAME = FQCH4P15 EXPOSURE_DURATION = 500.00 HST Target name: SATURN-EAST-ANSA Aperture type: PC1-FIX (PC1-WF4) MUCH OF SATURN 0307 ,"U2TF0307T.GIF","SATURN " TART_TIME = 1995-11-21T12:34:17 STOP_TIME = 1995-11-21T12:40:57 FILTER_NAME = FQCH4P15 EXPOSURE_DURATION = 400.00 HST Target name: SATURN-WEST-ANSA Aperture type: PC1-FIX (PC1) MUCH OF SATURN . . . 199511XX/U2TFXXXX/BROWSE NICHOLSON 1995-11-27 . . . I think that if you have such an index you can easily see which are the dates and the filters. A problem is "where are the images". With all the informations given in the header you cannot find this information anywhere and you are obliged to look at the images. In fact if you realize that there is some kind of code you can derive this information. Here for instance on some images is written "HST Target name: SATURN-WEST-ANSA". That means that the image has been taken on PC1 only. On others is written "HST Target name: SATURN-EAST-ANSA": the image is taken also on WF4. But the label "SATURN-EAST-ANSA" is wrong since you have both ansae. I think that since the kind of index I am proposing is not a "legal" one you could change the legal appelation "PC1-FIX" which gives only the information that the image has been taken on the right side of the mosaick by the appelations "PC1" or "PC1-WF4". Otherwise I am very impressed by the amount of excellent work made to help people to use this data set.