Discover the DATA behind the Drawing Using A+CAD. Permission to copy

Transcription

1 Discover the DATA behind the Drawing Using A+CAD Permission to copy

2 The CAD Academy Did you ever wonder how the entities you draw on the screen look in the database? Understanding how CAD stores data makes it easier to understand the program. Today we are going to take a peek at how A+CAD stores data using LISP. Launch A+CAD. Your screen should look similar to the screen at right. In order to play with entities we have to draw some entities. An entity is a line, arc, circle, etc. Select EXPLORE LAYERS as shown at right. Select EDIT and then NEW and then LAYER to create a NEW LAYER. Right mouse click and SELECT RENAME - name this layer PART and ENTER. You will have to BACKSPACE the old name out and type in the new.

3 Page 2 Double LEFT mouse click on the COLOR box to the right and SELECT a COLOR of your choice for this LAYER. You can also RIGHT MOUSE click on the NAME and CREATE a NEW LAYER that way as well. Create a 2 nd LAYER named OBJECT and give it a color of your choice. You should end up with two layers with colors of your choice Close EXPLORE LAYERS by Using the X at the top right and Check out your new layers

4 By clicking on the down arrow. Page - 3 SET to the OBJECT layer by selecting it. Type in C at the command line for Circle and press ENTER or select the circle command ARROW down and CHANGE the layer to PART and then SELECT line. Draw some LINES to the right of the circle. It does not matter what they look like as we are just going to use them to check out the DATA.

5 Page 4 At the command line we are going to type in the following (SETQ E1 (ENTSEL)) This should echo back SELECT ENTITY. Select the CIRCLE. The first thing inside of the parenthesis is ALWAYS a LISP function. So SETQ and ENTSEL are the LISP functions. SETQ means we are using E1 (called a VARIABLE) to stand for and store the information we are getting from ENTSEL. ENTSEL just means SELECT ENTITY. Press the function2 or F2 to see more of the TEXT if you can t see it all. It should echo back that it found the entity plus the X Y Z position on the screen. Ok, let s dig deeper. (SETQ E2 (ENTGET (CAR E1))) We are using LISP functions SETQ ENTGET CAR Entget means to get the entity (the circle) CAR means the first one and since we had only one it will get the circle.

6 Page 5 This is the actual DATABASE of the circle. Items with a period (0. CIRCLE ) are known as a DOTTED PAIR. You can use any and all of this information to write a program. Being able to access this data and do mathmatical functions opens a big world to those who need custom application. Dotted Pairs start with interesting information for instance: 0 = entity type (circle) 8 = layer name (object) Close the text box on the screen and let s play with the LINES. At the command line type in the LISP expression. (SETQ LL (SSGET)) SETQ and SSGET are our LISP FUNCTIONS. You basically make up logical or meaningful names for VARIABLES. SSGET makes SELECTION SETS. CAD operators work will selection sets all day long. Press ENTER. We notice how many items are in the selection set and also that CAD gives it a unique number. Now let s say we want to do something to the lines we stored in the variable LL. Type in M (or select Move) and enter. When asked to SELECT the items type in!ll (which is our selection set).

7 Notice that by typing in!ll A+CAD finds our select set without us having to pick anything. Page - 6 Press the ESC key to CANCEL the move. One more thing to try is to type in E and ENTER for erase. When prompted for the entities type in!ll and ENTER. The lines are gone. Programming is powerful, fun and exciting. Not everyone likes to program, but if you found this interesting we have more tutorials on programming with LISP available. stephanie@thecadstore.com to dig deeper. Remember DEFUN never ends when you use LISP. Lesson is complete.