Peter Briggs: mapslice - a map viewer for CCP4i

• User requirements
• Programming issues

User Requirements

The basic list of requirements from a user perspective is:

• Colour contours or level
• Specifying contour levels either absolute or rms
• Info about the map - rms and mean of density
• Dispaly PDB files (peaks or atoms)
  - need to be able to alter slab search distance & label atoms
• Scaleable (ie must be able to resize window)
• Plottable (ie must be able to print out)
• All harker sections
• Cursor position in fractional and/or absolute coordinates
• Choosing actual section and/or axis

This list is not in any order of importance.

Programming Issues

The basic mapslice program will consist of Tcl/Tk code interacting with external (non-Tcl) code of some description. The purpose is to perform the following basic functions:

1. Read in an arbitrary map section
2. Generate contour lines
3. Display the contours

My present thinking is that steps 1 and 2 should be performed by non-Tcl code, producing a set of Tcl drawing commands which are then executed by the Tcl code (step 3). Some possible ways of achieving this are:

1. Use an external program to read sections from a map directly each time a section is required. Call mapmask to reorder the map axes if sections along other axes are required.
   Issues:
   a. Requires calls to two programs (speed)
   b. Requires creating external temporary map files

2. Use an external program to read in a whole map each time a section is required. Any axis reordering can be done inside the program before generating the contours.
   Issues:
   a. Reading in a whole map is slower than reading in a single section

3. As (2) above, but: the external program runs "interactively" with the Tcl code. Each map is read into memory only once.
   Issues:
   a. Difficulties with extracting Tcl information from the interactive output.

Beyond this are options (?) which involving interfacing the Tcl directly with compiled Fortran (or C/Fortran) subroutines to read in and contour the sections. I really have no idea at this stage how feasible this would be, and how easy it would be to maintain.