capocad Posted February 5, 2021 Share Posted February 5, 2021 (edited) Hi! I have a question related to rtos and rounding real numbers. If i do the following in autolisp: (setq number 0.925) (setq roundedNumber (rtos number 2 2)) I get as a result "0.93", and that's ok, is what I expected. But if I do this: (setq ss (ssget)) (setq e (ssname ss 0)) (setq ent (entget e)) (setq dimValue (cdr (assoc 42 ent))) (setq roundedValue (rtos dimValue 2 2)) And select a dimension with a value of 0.925, the result is "0.92", despite both variable types, "number" and "dimValue" are REAL and have the same value. Does anyone know why this happen? Thanks in advance Edited February 5, 2021 by capocad Quote Link to comment Share on other sites More sharing options...
BIGAL Posted February 5, 2021 Share Posted February 5, 2021 I drew a line then offset 0.925 then did code and get 0.93 is the 0.925 an overide dimension ? Quote Link to comment Share on other sites More sharing options...
Lee Mac Posted February 5, 2021 Share Posted February 5, 2021 What is returned if you change (rtos dimValue 2 2) to (rtos dimValue 2 15)? Quote Link to comment Share on other sites More sharing options...
capocad Posted February 5, 2021 Author Share Posted February 5, 2021 23 minutes ago, BIGAL said: I drew a line then offset 0.925 then did code and get 0.93 is the 0.925 an overide dimension ? No, it's not a override dimension. 1 - I create a new file using acadiso.dwt as template 2 - Create a line of 0.925 length 3 - Create the dimension for the line using the default ISO-25 style 4 - Use this code to test: (defun c:testrtos( / ) (setq ss (ssget)) (setq e (ssname ss 0)) (setq ent (entget e)) (setq dimValue (cdr (assoc 42 ent))) (setq roundedValue (rtos dimValue 2 2)) (princ roundedValue) (princ) ) As a result, I get "0.92" Quote Link to comment Share on other sites More sharing options...
capocad Posted February 5, 2021 Author Share Posted February 5, 2021 12 minutes ago, Lee Mac said: What is returned if you change (rtos dimValue 2 2) to (rtos dimValue 2 15)? Despite creating the line of exactly 0.925, the result with (rtos dimValue 2 15) is "0.924999999999955". Is there any way to get 0.93 as a result to match what the dimension shows on screen? Quote Link to comment Share on other sites More sharing options...
BIGAL Posted February 5, 2021 Share Posted February 5, 2021 I did a line Length =0.92500000, Angle in XY Plane = 90d0'0" (setq x 0.924999999999955) 0.925 Command: (rtos x 2 2) "0.92" Command: (rtos x 2 3) "0.925" Command: (setq x 0.925) 0.925 Command: (rtos x 2 2) "0.93" Hmmmm ? Quote Link to comment Share on other sites More sharing options...
capocad Posted February 5, 2021 Author Share Posted February 5, 2021 I came to a clunky solution but it works: (defun c:roundDim (/ ss e ent dimValue d e f g) (setq ss (ssget) e (ssname ss 0) ent (entget e) dimValue (cdr (assoc 42 ent)) d (rtos dimValue 2 3) e (atof d) f (rtos e 2 2) g (atof f) ) (princ g) (princ) ) Although I'm not sure what's exactly the cause of the problem. Quote Link to comment Share on other sites More sharing options...
Lee Mac Posted February 6, 2021 Share Posted February 6, 2021 (edited) 20 hours ago, capocad said: Despite creating the line of exactly 0.925, the result with (rtos dimValue 2 15) is "0.924999999999955". Is there any way to get 0.93 as a result to match what the dimension shows on screen? The value of 0.924999...955 is a consequence of the accuracy problems associated with the double-precision floating-point format used to store real numbers in computer memory - this is described in more detail here, here, and here. Your code demonstrates one possible way to cater for this, however, note that your method would yield undesirable results for measurements such as 0.9249: _$ (rtos (distof (rtos 0.9249 2 3) 2) 2 2) "0.93" _$ (rtos 0.9249 2 2) "0.92" As such, a safer way to account for the rounding of doubles would be to add a small tolerance to the original value prior to rounding, e.g.: _$ (rtos (+ 1e-8 0.924999999999955) 2 2) "0.93" _$ (rtos (+ 1e-8 0.9249) 2 2) "0.92" However, note that retrieving the dimension measurement value and rounding to a given number of decimal places may still not yield a string which matches that displayed by the dimension, as a result of dimension style configuration - to obtain the value displayed by the dimension, you can obtain the MText content found within the dimension block, e.g.: ;; Get Dimension String - Lee Mac ;; Returns the displayed content of a dimension (defun LM:getdimstring ( ent / enx rtn ) (if (and (setq enx (entget ent)) (wcmatch (cdr (assoc 0 enx)) "*DIMENSION") (setq ent (tblobjname "block" (cdr (assoc 2 enx)))) (setq ent (entnext ent) enx (entget ent) ) ) (while (and ent (null rtn)) (if (= "MTEXT" (cdr (assoc 0 enx))) (setq rtn (cdr (assoc 1 enx))) ) (setq ent (entnext ent) enx (entget ent) ) ) ) rtn ) Edited February 6, 2021 by Lee Mac 2 Quote Link to comment Share on other sites More sharing options...
capocad Posted February 6, 2021 Author Share Posted February 6, 2021 Thanks so much Lee!! That "Get Dimension String" function was exactly what I was looking for, much better than my clunky solution. Quote Link to comment Share on other sites More sharing options...
Lee Mac Posted February 6, 2021 Share Posted February 6, 2021 You're most welome! Glad it helps Quote Link to comment Share on other sites More sharing options...
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