densify

Description

This program is used to increase the resolution of a shape model by interpolating heights between landmarks.

densify 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

• LMRKLIST.TXT - List of all landmarks to be used

• LMKFILES/ - Directory of .LMK files for each maplet

• MAPFILES/ - Directory of .MAP files

• SHAPEFILES/ - Directory of built shapes

Optional Files

• LMRKLISTR.TXT - Specific list of landmarks desired

== Using densify ==

The input commands for densify are usually prearranged in a file, which is then used by entering:

~/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)

• Should we do the following according to the lines in the code above??? And present as if user is typing the lines in??

The initial inputs to densify are:

• the names of the input and output SHAPE file
• a multiplicative scaling factor K (usually 2)
• a limit in km specifying how far along the surface normal the program should search for a maplet
• a random seed in the form of a large integer.

  • This random seed is superceded if you enter one on the command line after you invoke densify.

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).

densify 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.

The program now 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:

• SHAPE0 for Q=64
• SHAPE1 for Q=128
• SHAPE2 for Q=256
• SHAPE3 for Q=512

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

• cp SHAPEFILES/SHAPEX.TXT SHAPEFILES/SHAPE2.TXT

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

• cp SHAPEFILES/SHAPEX.TXT SHAPEFILES/SHAPE3.TXT

SHAPE.TXT is also Q=512 and you need to update that as well. For historical reasons, some scripts change permissions on SHAPE.TXT to read only. At the command line enter:

• chmod +w SHAPE.TXT cp SHAPEFILES/SHAPEX.TXT SHAPEFILES/SHAPE.TXT

Output

• SIGMA.TXT - list of sigma values associated with the shape model (found in SHAPEFILES/)

• Shape file in ICQ format

(Compiled by TC)

CategoryPrograms