densifyA

Description

This program is used to increase the resolution of a shape model using albedo between landmarks.

densifyA first constructs a reference surface by interpolating the surface points of a lower resolution shape model. At each point of the reference, there is a vector V0 from the model center to that point and a normal N0 to the surface. That normal is extended some distance until it pierces one or more of the ensemble of maplets, and the average A of those distances is taken to represent the piercing point on the new model's surface. The new surface vector is V = V0 + A*N0.

(./) I need something to set up this image. It depicts ??? 

                ___...-------...___
                   |           |
                   |           |A*N0
             ______|___________|_________ reference
                   \          /
                    \        / V0
                     \      /

At the early stages (./) of what??, there are mismatches in maplet locations simply due to the formal uncertainties of the estimation process. Therefore, we have found it better to average the maplet normals N at each point, keeping a small randomly selected set of the A as conditioning heights.

Required Files

Optional Files

Output Files

Using densifyA

Although densifyA can be run interactively, the input commands are usually prearranged in a file (e.g., "tmpRun.txt") and you invoke the program from the command line like this: 

~/bin/densify < tmpRun.txt

Here is a sample "tmpRun.txt" file showing the input commands: 

SHAPEFILES/PreviousShapeFile       (input shape)
2 100 1.67773                      (K (power of 2), search range (km), random seed)
SHAPEFILES/CurrentShapeFile        (output shape)
1                                  (more iteration)
.005                               (fraction of points used for conditioning)
.025                               (conditioning weight)
1                                  (more iterations)
1
1
1
1
1
1
1
1
1
1
1
1
1
0                                  (end program)

The input commands are:

In most cases, the maplets will cover most of the surface. Where it is not covered, the normals to the input model provide the "slopes" and the integration proceeds without any randomly chosen conditioning heights from these areas.

In some cases, such as fast flybys of small bodies, only a small fraction of the surface is visible and vast areas are unknown. In these cases, conditioning heights are also taken from the input model as well. Specify this option by using a negative value for K (usually -2).

densifyA then determines the average height along each surface normal from each reference point of the densified shape. It also determines the average maplet surface normal and the standard deviation of the heights, used as a measure of uncertainty. It produces the output SHAPE file and a similar file called SIGMA.TXT that has an extra column representing the uncertainty. SIGMA.TXT can be displayed as an image to show areas that might need further work.

After it completes the commands in the file, densifyA gives these options: 

     0. end program
     1. proceed to iteration

If you enter '0', the output shape model will be the height averaged result.

The entire script, with the output model called SHAPEX.TXT, looks like this: 

     densify
     SHAPEFILES/SHAPE1.TXT        < input shape
     2, 1.0, 5639                 < K, search range (km), random SEED
     SHAPEFILES/SHAPEX.TXT        < output shape
     0                            < end program

If you enter '1', the program prompts: 

     input fraction

Enter the fraction of averaged heights (and empty heights if K<0) used to condition the integration (usually '.005').

The program prompts: 

     input weight

Input the weight given to the conditioning heights (usually '.025').

The program produces an output SHAPE file and gives these options: 

     0. end program
     1. more iteration
     2. change weight

The interim shape can be viewed to see whether you want to change the weight given to the conditioning heights using the procedure described below. Usually, you just continue iterating or, finally, exit the program.

By tradition, usually use:

If there have been no problems after you complete this run, at the command line enter:

After another densification, when SHAPEX.TXT is Q=512, at the command line enter:

SHAPE.TXT is also Q=512 and you need to update that as well.

At the command line enter:

Interactive

If you want to run densifyA interactively, the initial inputs are:

densifyA will then prompt you for the remaining inputs and iterations.

(Compiled by TC)

CategoryPrograms