This program shows how well SPC has performed. residuals tests the landmarks to look for problems and gives reports about how well the landmarks were processed. The reports it generates are listed in the Output section.
LMKFILES/ - a directory containing the full suite of landmarks
NOMINALS/ - a directory containing the image .NOM files (starting solution image, S/C and camera information)
SUMFILES/ - a directory containing the image .SUM files (updated solution image, S/C and camera information, lmrks and limbs)
IMAGEFILES - a directory containing the image .DAT files
LMRKLIST.TXT - a list of the landmarks contained in the solution
check.txt - List of landmarks and overlaps for landmarks whose linear residual is greater than the user-specified limit.
FLATLIST.TXT - List of flat maps (landmarks containing no topography).
MAPCHK.TXT - List of maplets whose difference between predicted and observed pixel/line locations in attached images is greater than a user-specified limit, or who have two or fewer overlaps attached to them.
MAPRES.TXT - Maplet resolution information for maplets contained in at least one picture or limb.
no_update.txt - List of landmarks whose associated pictures are not listed by increasing mission time in the .LMK file.
After you invoke the program, it prompts:
enter 3 values (px,km,km)
value 1 - the value of the pixel residual limit. Images and maplets are flagged for a pixel residual limit greater than this.
An image in a landmark will be flagged if the RSS of the pixel and line residuals in units of image pixels exceeds the input value
value 2 - the value of the linear residual beyond which images and maplets are flagged.
An image in a landmark will be flagged if the RSS of the pixel and line residuals in metric units (km) exceeds the input value
value 3 - the max scale (km/px) that sets the scale for the histogram at the end of PICINFO.TXT.
The two criteria, km and pixels, allow flexibility when there are images of great range in resolution in the same landmark. These criteria also apply for outliers in the limb apparitions of images in landmarks and in the case of the metric criterion, second input parameter, for the map-to-map overlaps. The limb and overlaps outliers are collected in the file veto.txt and you can delete them from the landmarks by running lithos with veto.txt as input.
Here is a sample of inputs for residuals:
10, 0.01, 0.01
Here is a sample MAPINFO.TXT file:
Here is a sample of a single landmark in RESIDUALS.TXT:
The following shows what a bad and a fixed image look like:
Figure 00: Results from Using Residuals to Improve Processing
residuals is not the only way to check how well SPC performed. You can simply observe the maplets generated.
Here is a list of what to look for when you visually inspect a maplet to judge its quality:
- Verify that the quantitative error estimates are believable.
- Render a single maplet, or a DEM synthesized by a collection of maplets, at the same geometry and illumination conditions as the images themselves.
- Determine if all the features in the images appear in the DEM.
- Determine if the smallest discernible features in the images (e.g., boulders, craters etc.) are visible in the DEM as well.
- Determine if the relative albedo solution is such that the relative brightness of adjacent image features matches that of the DEM.
- Determine if the heights solution is such that the length and overall appearance of the shadows in the DEM match those of the image.
How Uncertainties are Introduced in the Data
These are the main types of uncertainties and how they manifest:
- S/C trajectory, camera pointing, image timestamp
- Manifest themselves mostly in the projection of image template onto the surface. Corrected by global geometry solution.
- Image noise, artifacts, smear, overall image quality
- Manifest themselves in predicted image template brightness and in its fit to the extracted image brightness.
- Photometric model and reflectance function models
- Show up in slopes and heights integration
- Poor choice of a-priori parameters and data weights
- Are evident at the end of each estimation step. Data won’t fit well.
Often the above contributions are correlated; you may not be able to separate individual contributors until you have taken many processing steps.
If overlap and limb weights in INIT_LITHOS.TXT (i.e. PICWTS and LMKWTS keyword) are set to 0, then RESIDUALS.TXT will not display the residuals of these values.
(Compiled by KD)