4.207: Sample AutoLISP

Entity Data

4.207 | Tutorials and Samples
write requests to: takehiko@mit.edu
last revised : 2/5/01
AutoLOADERŠ Set Up

AutoLISP file, Part 1

entdata_01.lsp: : this program provides functions to manipulate entity data.

Functions Defined (click button for dispatching to AutoCAD)

(c:demo)

: no demo available currently.

(print_entity_data entity)

: prints entity data of the given entity line by line. If the specified entity does not exists, the function will prompts for a selection. It uses entget command.

The following displays the entity data associated with the given line entity.

(print_entity_data line_1 )

When you specify non-entity value (such as nil) for the parameter, it will ask you to choose an entity.

(print_entity_data nil )

To know the meaning of the printed data, you need to know the AutoCAD DXF group code. Here is an example of the information returned by entget command.

 (  
  (-1 . <Entity name: 1016f950>)     ; entity name (changes when a file is re-opened.) 
  (0 . "LINE")                       ; entity type
  (0 . "CIRCLE")                     ; entity type 
  (5 . "462")                        ; entity handle (stays the same in a re-opened file.) 
  (40 . 60.0)                        ; radius for a circle (must be described in float.)
  (67 . 0)                           ; indicates model or paper space
  (8 . "layer1")                     ; layer
  (62 . 1)                           : color number (If by-layer, this is omitted. If by-block 0) 
  (10 0.0 0.0 0.0)                   ; primary point (an endpoint for a line entity)
  (11 100.0 100.0 0.0)               ; another point (the other endpoint for a line entity)
 )

Look into this excerpt from AutoCAD Customization Guide Appendix C, "DXF Group Codes". for other group codes.

(get_data_for_group_code group_code entity)

:returns the information associated to the group code in the entity data of the given entitye by line. If the specified entity does not exists, the function will prompts for a selection. It uses entget command.

The following extracts the coordinates corresponding to the group code 10 (endpoint for a line, center point for a circle) from the given line entity.

(get_data_for_group_code 10 line_1 )

When you specify non-entity value (such as nil) for the parameter, it will ask you to choose an entity.

(get_data_for_group_code 10 nil )

(change_data_for_group_code group_code entity new_value)

:changes the information associated to the group code in the entity data of the given entitye by line. If the specified entity does not exists, the function will prompts for a selection. It uses entget, entmod and entupd command.

Notice that not all the values associated to an entity's group codes are changable. Some (such as entity type, entity handle and entity name) are read only.

The following changes the coordinates corresponding to the group code 10.

(change_data_for_group_code 11 nil (list 100 200 0) )

The following changes the entity's layer (group code 8).

(change_data_for_group_code 8 nil "y_layer" )

*** Information below this line is not compatible with AutoCAD R2000 ***

AutoLISP file, Part 2

entdata_01b.lsp: : this program provides additional functions to manuplate complext entity data such as AutoCAD pline.

Functions Defined (click button for dispatching to AutoCAD)

(c:get-pline-vertices)

:prints all point coordinates of selected pline's vertices. This only deals with a pline made of lines (that is, no arc).

(c:get-pline-vertices)

Here is how it works. If you issue (entget pline-entity), it will return something like this.

 (  
  (-1 . <Entity name: 1016f950>)     ; entity name (changes when a file is re-opened.) 
  (0 . "PLINE")                      ; entity type
  (8 . "layer1")                     ; layer
  .....                              ; other information 
 )

Next, you can get its first vertex by issuing

  (setq  first-vertex (entnext pline-entity))

The result of (entget first-vertex) will then be .

 (
  (-1 . <Entity name: 1016d580>)     ; entity name of the component point
  (0 . "VERTEX")                     ; entity type is "VERTEX"
  (8 . "layer1")                     ; layer
  (10 10.5462 28.3899 0.0)           ; DXF group code 10 gives xyz coordinates
  ..... 
 )

You can repeat the process to get all other vertices. For example,

  (setq  second-vertex (entnext first-vertex))

When you exceed the last vertex, what happens then?

  (setq  end-marker (entnext last-vertext))

The result of (entget end-marker) will then be

 (
  (-1 . <Entity name: 1016d582>)     ; entity name of the termination marker
  (0 . "SEQEND")                     ; entity type "SEQEND" signals the end of vertices
  (5 . "37")
  (100 . "AcDbEntity") 
  (67 . 0) 
  (8 . "0") 
  (-2 . <Entity name: 1016f950>)     ; DXF group code -2 points back at the pline entity
 )

Standard AutoCAD Commands

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