(Instruction 511 in OR TEP-II has been renamed as 1001 in ORTEP-III. Instruction 511 continues to work as it did in OR TEP-II, but users should use 1001 in the future since 1001 has greater versatility.)

Instruction 1001 activates the hidden line removal feature of ORTEP, which corrects the illustration for overlapping atoms and bonds. It stores the projected atom boundary ellipses for all atoms in the ATOMS array. It is important that the contents of the ATOMS array, the scaling and positioning, and the structure orienting parameters (controlled by the 400, 600, and 500 series of instructions, respectively) not be changed between the 1001 instruction and the drawing of the atoms and bonds by the 700 and 800 series of instructions. Otherwise, the projected outlines may be destroyed or become inappropriate.

The projected outlines of bonds are approximated as quadrangles. Those of implicitly specified bonds may be stored for overlap correction by adding Format No. 2 trailer cards to the 1001 instruction that are identical to those of the 802/812 instructions used subsequently for plotting the implicit bonds. Alternatively, implicitly specified bonds may be stored with one or more 822 instructions with the Format No. 2 trailer card set. A 1001 instruction must precede the first 822.

If more than one 802/812 instruction is used to draw the bonds, there should be a corresponding 822 provided for each. This allows different atom features to be treated separately with separate 822 (and corresponding 802/812) instructions.

Explicit bonds may only be stored by using one or more 821 instructions following a 1001 instruction. These will be identical to the 801/811 instructions (except for the instruction number) used subsequently for plotting the explicit bonds. The thiourea-tellurium example illustrates the use of the 821 instruction.

As currently dimensioned, the maximum number of projected atoms and projected bonds that can be stored is 500 and 599, respectively. A list of the projected atoms and bonds is given in the ORTEP output file.

The projected outline information for atoms and bonds must be recalculated for each member of a stereo pair; consequently the 1001 and 821 or 822 instructions are usually the first instructions within the save sequence. The old overlap information is deleted whenever a 500 or 600 series or 1001 instruction is executed.

All details inside atoms and bonds, including chemical symbols and bond-distance labels, will be corrected for overlap. Chemical symbols drawn by 700 series instructions and bond-distance labels drawn by 800 series instructions that are outside the atoms or bond boundary will not be corrected for overlap unless the overlying atom or bond outline actually intersects (in projection) the atom or bond being drawn. Labels and symbols drawn with the 900 series instructions will not be corrected for overlap.

• 1001: Projected Outline Storage
• 821: Explicit Bond Outline Storage
• 822: Implicit Bond Outline Storage

A constant width overlap margin (i.e., a blank strip at the intersection of overlapping elements) is included in the dimensions of each projected atom ellipse and projected bond quadrangle. The width of this margin (in inches) may be specified as a parameter with the 1001 instruction if desired; otherwise, the margin is set by default. The default value is calculated as follows:

for SCAL1 < 0.25: OVMRGN = max (0.010, SCALl^1/2 0.05)

for SCAL1 0.25: OVMRGN = max (0.025, SCALl^1/2 0.03)

Some users prefer an overlap margin of 0.0 for stereoscopic drawings.

If the value in column 3 is "2", Format No. 2 trailer cards are included. In general, all the trailer cards included with the 802/812 instruction sets are used.

New on this card in ORTEP-III is the second parameter, which specifies the number run type of the number runs that follow on the Format No. 2 trailer cards.

If explicit bonds are to be stored for the overlap correction, the attached atoms must be in the ATOMS array even though this is not a requirement for the 801/811 instructions used for plotting the explicit bonds. In general, the 821 instructions will be identical to the 801/811 instructions (except for the instruction number) used subsequently for plotting the explicit bonds. The thiourea-tellurium example illustrates the use of the 821 instruction.

Usually, the information on implicit bond outlines is stored with the 1001 card. However, if more than 20 Format No. 2 trailer cards are needed to specify all bonds, the extra ones can be entered with this instruction. Also, 822 instructions in addition to the 1001 may be used to treat different atom features in different ways. In general, the 822 instructions will be identical to the 802/812 instructions (except for the instruction number) used subsequently for plotting the implicit bonds. The thiourea-tellurium example illustrates the use of the 822 instruction.

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Page last revised: July 11, 1997