Using Visual PinPoint

Introduction

Visual PinPoint is designed to make it fast and easy to plate solve and then scan sets of images for asteroids or supernovae. The automatic asteroid detection capabilities of PinPoint are unmatched in any commercially available software, and on a par or superior to most professional surveys' capabilities. The supernova detection capability is limited somewhat b the object inventory method used. Nonetheless it is useful for finding supernovae that are not heavily merged with a galaxy.

Plate Solving

There are two steps needed to use Visual PinPoint for asteroid or supernova searching. The first step is the same for either task: plate solve all of the images. Plate solving is the process matching stars in the image to known stars in a reference catalog and writing transformation info to the FITS header. This transformation info – the World Coordinate System (WCS) data – allows a FITS image to be used for direct astrometric measurements since the image scale, projection geometry, and center-point coordinates are accurately known. If the original FITS image has WCS data, it will be used as a starting point for PinPoint's plate solving process.

Requirements

• FITS image, various bit depths are supported
• You must know the approximate plate scale of your images, in arc seconds per pixel.
• FITS header has RA or OBJCTRA and DEC or OBJCTDEC fields which specify the approximate coordinates of the center point of the image. If this is missing, and you don't have all-sky solving enabled, Visual PinPoint will prompt for the coordinates and optionally save them to the FITS header permanently.

Note that the scale and approximate coordinates are not needed if you use all-sky solving (which will be much slower, and which requires an internet connection). This is available as an option on the Solve Plates tab.

One-Time Setup

1. In the Solve Settings tab of Visual PinPoint, set up the path and type for your reference catalog. Normally this will be the GSC/1.1 on the PinPoint CD-ROM, so just enter the drive letter of the CD (include the colon only), for example "D:" and select "GSC/1.1 Catalog with enhanced accuracy".
2. Enter the horizontal and vertical plate scale of your images. These will be the same unless your imager has non-square pixels (extremely rare nowadays).
3. If your imager is filtered, change the Color Band from the default Unfiltered to the best fit Johnson-Cousins color band for your imager. If you are imaging unfiltered, be sure to leave it set to "'Unfiltered".
4. Leave everything else at the default settings: Min Size = 2, Min Sigma = 2.0, Centroid = PSF, Projection = TAN, Catalog Expansion = 30%, Catalog Max Mag = 18, Solver Parameters = 0 except Maximum # Stars = 500 and Max Time = 60.

Sequence

1. In the Solve Plates tab of Visual PinPoint, use the Add Files button or drag and drop to put a few of your images into the list window.
2. Select Test - Never add WCS.
3. Click Solve Plates. Normally you'll get a plate solution for each image. If you have trouble, see Troubleshooting below.
4. Switch to Add WCS if none present.
5. Again, click Solve Plates. That's it! The WCS is in your images and they are ready to use.
6. Note the plate scale in the solution report. Enter this into the Solve Settings tab (no need for minus signs). Now your estimated plate scale is very accurate. This can reduce the solution time in the future.

NOTE: Once you get PinPoint set to reliably solve your images, you don't need to run solutions in Test mode any more.

The Force Image Rescan Option (Solving)

If you change any of the object detection settings in Solve Settings, and you want to try solving with the new settings, be sure to turn this option on. It will cause the ".stars" file(s) to be deleted, forcing the image to be re-scanned with the new settings.

All-Sky Plate Solving

If you have an internet connection, and if you have images for which the above requirements can't be met (no approximate coordinates and/or unknown plate scale), you can use all-sky plate solving. In the Solve Plates tab, check the box labeled All-Sky Solving. Then proceed as above. It may take considerable time. When the results come back, PinPoint will then use that info to perform a full local solution and update the WCS.

Note that in Solve Settings, there is an option to force the use of the actual image at Astrometry.net. Normally, PinPoint does the source (star) detection locally using your detection settings and centroiding method (you can use SExtractor on really difficult images). The list of detections is then sent to Astrometry.net for all-sky solving. If you are having problems with a set of images, you can try letting Astrometry.net's detector work on the actual image instead of PinPoint. This will further slow things, of course, because the large image data must be transmitted to the (remote) Astrometry.net server.

Solve Settings - All-sky service domain:port

This field is used to tell the PinPoint engine the internet address of the all-sky solving service. It defaults to nova.astrometry.net which is the online service provided by Astrometry.Net. As described in all-sky plate solving, you can install ansvr, a local all-sky solving engine and server, then use that for all-sky solving without an internet connection. In that case, assuming you installed ansvr to your local machine, use 127.0.0.1:nnnn where nnnn is the port you assigned to ansvr on installation.

Troubleshooting Plate Solving

• If you have an internet connection, enable all-sky solving. This will be much slower but it will solve regardless of how far off the center point and scale hints are. Otherwise...
• If your images don't plate solve first double check your plate scale. This doesn't have to be super accurate but if it is off by 25% or more (outside the range of 75% to 125% of the actual) it could prevent solution.
• Check the approximate center point coordinates. If these are off by half a field of view or more, it can cause solution failures. Use All-Sky solving if possible. Your images must be within half a field of view at a minimum, and if the area is star-poor, it may need to be much closer than that. PinPoint must have at least 8 matching stars to make a solution.
• Once you have a good solution, update the plate scale in your settings. It doesn't hurt if it's close to correct!

The Force Image Rescan Option (Searching)

If you change any of the object detection settings in Asteroid or Supernova, and you want to try searching (only) with the new settings, be sure to enable Force Image Rescan. It will cause the ".stars" file(s) to be deleted, forcing the image to be re-scanned with the new settings. Normally you'll use the stars that were detected during plate solving, maximizing your searching efficiency by allowing you to skip re-scanning the image(s).

Asteroid Searching

Requirements

• Images must be plate solved by PinPoint. Other programs will not include the optical distortion mapping that PinPoint does, and therefore your postions will not be as accurate as PinPoint is capable of producing. For somme optical systems this can result in gross astrometric errors.
• Images must have been solved using an MPC-acceptable reference catalog. As of 2013, the USNO UCAC4 catalog is the preferred choice.
• One or more sets of images of the same area (no practical limit)
• Two images in a set for manual detection via blinking
• Three or more images in a set for automatic and/or manual detection

One-time setup

In order to get the most out of Visual PinPoint's automatic detection feature, you must do the engineering tests needed to establish your limiting magnitude and the exposure duration needed to reach it! See step 7 below.

1. In the Asteroid Settings tab of Visual PinPoint, fill in the MPC Report section. For info on what all of this is, see the Minor Planet Center Specifications for this info.
2. If you are using TDI (drift scanned) images, check the Enable TDI corrections box. This applies observation time corrections.
3. If you are doing high-precision work and wish to report this extra precision to the MPC, check the Enable high precision reports box. This makes the RA precision 0.001s, Dec 0.01s and observation time to 0.000001 days. NOTE: Do not use this unless you meet the requirements of the MPC as described on this web page, namely where such precision is justified.
4. Most people search for asteroids with unfiltered imagers. If your imager is filtered, be sure to select the appropriate Johnson-Cousins color band in the Solve Settings tab before solving your survey images. This will result in the correct color band being reported in your MPC reports. Note that 'R' is reported for unfiltered images, and no color is reported for B-band images. This is per the MPC's reporting preferences.
5. Normally, the Object Detection section is not used, since the detection list is saved from plate scanning. Only if you are processing images with no saved scan list (or if you turn on Force Image Re-Scan) will these settings be used. Typically you will use the same high-sensitivity settings as you used in the Solve Settings tab.
6. If you solved your images in another VPP session verify that the reference catalog you used for solving is still set in the Solve Settings tab. Thjis will result in the correct catalog appearing in your MPC reports.
7. In the Acceptance Tests section, the most important items are the Limiting Mag and @Exposure settings. This determines what PinPoint considers to be "impossibly faint" and is scaled by the exposure duration. Here's how to get this right:
   1. Take a series of images of increasing exposure length. Make each one about twice as long as the previous. The actual length depends on your setup and skies. The goal is to reach your limiting magnitude, the point beyond which longer exposures will not result in fainter stars being recorded. Pick a "good" night for these tests.
   2. Plate solve your test images in Visual PinPoint. The report will include a limiting magnitude and exposure interval for each image. If you are successful, you'll notice that the limiting magnitude will reach a maximum (faint) value and not go any fainter on longer exposures.
   3. Note the limiting magnitude and the shortest exposure duration that gets you there.
   Now enter these values into the Limiting Mag and @Exposure settings fields.
8. Leave the rest of the Acceptance Test settings at their default values: Min X-Y = 0.5 pixel, Max Fit Residual = 0.75 pixels, Max Trail = 3 pixels.

Sequence

1. In the Find Asteroids tab of Visual PinPoint, use the Add Files button or drag-and-drop to put a few sets of your images into the list window. They will automatically organize themselves into sets in a tree display. You can also use the Get Solved button to automatically transfer any images listed in the Solve Plates list into the Find Asteroids list.
2. Select Blink All Image Sets.
3. Select Brief tracing.
4. Click Find Asteroids. All sets containing three or more images will be scanned for asteroids, and those that are found automatically will be entered into a database.
5. After a while a blink display will appear. If there are automatically detected asteroids, they will be indicated by cross hairs. The yellow/green marked one is the one you are verifying. If you think it's real, click Accept, otherwise click Reject. Repeat for all automatic detections.
6. Eventually the blink display will switch to manual mode. You can tell this my the appearance of the Report button in place of the Accept button. You will see all of the automatic detections and previously reported manual detections marked by blue cross hairs.
7. If you see an unmarked asteroid, click anywhere once to stop the blinking. Use the mouse or F6-F7 keys to step between the frames and mark the asteroid. Click Report to add it to the MPC report.
8. Repeat for each manual detection. When you have reported everything you found manually, click the Done button.
9. A report containing information on automatic detections, and MPC report lines for accepted automatic detections and all manual detections will be in the file. To get only the MPC report info, turn off tracing.

Troubleshooting Asteroid Searching

If so, then the object detection did pick it up, but it failed some test of non-uniform motion, brightness, or brightness variation. The Limiting Magnitude and @Exposure will impose an "impossibly faint" limit on automatic detections. The Max Trail imposes a maximum speed limit. If the asteroid would have moved (e.g.) more than 3 pixels during the exposure, it is moving too fast and will be rejected. If the astrometry is bad or noisy, maybe the least-squares test for straight-line motion at a constant speed failed. Increase the max Fit Residual to 1 or 1.5 pixels and try again. You can turn on High tracing and try to figure out the massive amount of output. If you get this desperate, ask me to analyze a set of images and I'll try to figure out what's happening.

If you cannot mark the object on all frames in the set, then either the detection sensitivity is too low, or the object is merged with something else on one or more frames. More images in a set will reduce false detections, but it will also increase false rejections and cost you sky coverage. You have to determine where to operate in this space. You are the astronomer! If you change the detection settings in the Asteroid Settings tab, be sure to enable the Force Image Rescan option so the new settings will be used to detect objects.

Supernova Searching

This works similarly to Asteroid searching. For supernova searching, you need to put pairs of images into the list. One image of each pair is the "reference" image which does not contain any supernovae. The other, the "search image" may contain objects that are not present in the reference image. Visual PinPoint will attempt to identify objects present only in the search image. It does this by inventorying detected objects in each image, then eliminating those that appear in both.

If you are willing to learn about SExtractor, you can use this tool from within Visual PinPoint to scan supernova search and reference images. While much slower than PinPoint's built-in image scanner, SExtractor has superior abilities to pick out point sources out when embedded in galaxies and nebulae. For more information on PinPoint's integration with SExtractor, see the page on the Plate.UseSextractor property.

Visual PinPoint will not detect extremely faint supernovae, or those buried deeply within a galaxy core. It is useful for detecting fairly bright supernovae towards the edge of galaxies. SNe detection software used by the professionals is far more sophisticated and complex to use than Visual PinPoint, and is optimized for a particular telescope. Blinking gives your eyes a chance to be that sophisticated detector!

Requirements

• Images must be plate solved by PinPoint
• Exactly two images of the same area. They may be from different telescope/imager systems.

One-time setup

1. Start with the default settings for Supernova Detection and Reference Detection:

   Setting	Supernova	Reference
   Min Flux	500	0
   Sigma	4.0	3.0
   Filter FWHM	1.0	1.0

2. Always use the Filter, set for 1.0 pixel FWHM. This filter is an edge enhancer, and will do wonders for bringing stars out of galaxies.
3. Do not mess with Size Gain or Min Distance. Contact DC-3 Dreams support if you want more info on these.
4. In Common Detection, start with Min Magnitude of 15. If you think you can reliably image deeper, try increasing this (going fainter) after you get some experience.
5. Leave Galaxy Box at 0.0 to start with. This is used to restrict the search to the central area of an image, to reduce false detections. If your telescope points very well, and you typically shoot small galaxies, you can eventually try setting this to enclose the galaxy area.

Sequence

1. In the Find Supernovae tab of Visual PinPoint, use the Add Files button or drag-and-drop to put a few sets of two images into the list window. You can also use the Get Solved button to automatically transfer any images listed in the Solve Plates list into the Find Supernovae list.
2. Select Blink All Image Sets.
3. Select Brief tracing.
4. Click Find Supernovae. All sets will be scanned for supernovae, and those that are found automatically will be entered into a database.
5. After a while a blink display will appear. If there are automatically detected supernovae, they will be indicated by cross hairs. If you think a detection is real, click Accept, otherwise click Reject. Repeat for all automatic detections.
6. Eventually the blink display will switch to manual mode. You can tell this my the appearance of the Report button in place of the Accept button. You will see all of the automatic detections and previously reported manual detections marked by blue cross hairs.
7. If you see an unmarked supernova, click anywhere once to stop the blinking. Use the mouse or F6-F7 keys to step between the frames and mark the supernova. Click Report to add it to the report.
8. Repeat for each manual detection. When you have reported everything you found manually, click the Done button.
9. A report containing information on automatic detections, and report for accepted automatic detections and all manual detections will be in the file. To get only the basic report info, turn off tracing.

Troubleshooting Supernova Searching

If not, then your search image detection parameters are not set sensitive enough. Try reducing the sigma first. Re-scan (make sure Force Image Rescan is on) and try again. Eventually, you'll reach a point where there are too many false detections are made. This is the limit of PinPoint's capability.