What is actually a "Graphic Group"?

Question

Hi. 
 I see 2 ways to create a Group in MicroStation: 
 - Group 
 - Named Group. 
 
 Group is very limitated because I understand we cannot add/remove elements later. And it is basically a Cell. 
 I understand that "Graphic Group" is a Named Group... 
 
 Because tools such as "Add to Graphic Group" and "Remove From Graphic group" are only for "Named Groups". 
 http://www.mdlapps.com/microstation/ustnhelp286.html#F26021 
 
 There is also "Graphic Group Lock" (ON /OFF) for Named Groups. 
 
 Why Bentley differenciates between Graphic Group and Named Group? is not the same? Is the old name of Named Group? 
 
 Thanks.

Jon Summers · Accepted Answer

Joan Martínez Serra said: Why Bentley differenciates between Graphic Group and Named Group? 
 Graphic Group 
 A Graphic Group (GG) is legacy technology &mdash; it's been part of MicroStation for decades. When you create a GG the operation is intrusive &mdash; meaning that it modifies the elements being grouped... 
 
 MicroStation finds the current GG value (it's stored in the DGN file) 
 MicroStation assigns that GG value to each selected element and rewrites the element 
 MicroStation increments the stored GG value 
 
 Depending on the state of the GG lock, you can modify all elements in that group . 
 Named Group 
 Named Groups (NG) are a 21 st century invention. NGs are non-intrusive &mdash; they don't modify the selected elements. 
 NGs are much more versatile than GGs. They have structure, behaviour and hierarchy. 
 Anonymous Cell (Group Command) 
 The group command ( Ctrl-G ) is another legacy tool. Select some elements, then use Ctr-G to convert them to components of an anonymous cell.

Jan Šlegr · Answer

Hi Joan, 
 Joan Martínez Serra said: Why Bentley differenciates between Graphic Group and Named Group? is not the same? Is the old name of Named Group? 
 As Jon explained, they are not the same. There were invented for different formats, internally implemented in very different way and offer different set of features. 
 In MicroStation, you can find more features and tools with similar functionality. These duplicity exists because of long MicroStation history, when old features have to be maintained, even when replaced by new tools. 
 Joan Martínez Serra said: I understand that "Graphic Group" is a Named Group... 
 GG and NG are completely independent and separated. I think there is no overlap, so no settings can be used both for GG and NG. It's true that Add to GG tool allows to add element(s) to GG or NG, but technically they are two tools, represented by one icon. 
 Joan Martínez Serra said: Group is very limitated because I understand we cannot add/remove elements later. And it is basically a Cell. 
 Yes, they are limited (because of GG concept age), but you are not right in the rest of your statement. 
 Graphic Group is the feature inherited from DGN V7 format. It's "a number only". All elements with the same value belong to the same graphic group. When GG lock is on, elements in the same GG are treated as one element. When the lock is off, GG information is ignored. 
 It's possible to manipulate with GGs (there are Add to GG and Drop from GG tools), but it is not very user friendly. 
 Joan Martínez Serra said: Named Group 
 As Jon wrote, Named Group is modern variant (a successor) of GG. They were invented when DGN V8 format was introduced. 
 NG offers plenty of new features: 
 
 They are "named", instead of "no information" number of GG 
 They can be hiearachical 
 An element can belong to more NGs at the same time (whereas element can belong only to one GG) 
 NG can contain elements from active model, from direct references and also nested references 
 Propagation rules can be set 
 
 Some MicroStation tools still use GG to work as in the past, but for user, NG should be the first and the only choice. 
 With regards, 
 Jan

Jan Šlegr · Answer

Joan Martínez Serra said: So "graphic group" is just an internal value? 
 Yes. Every graphics element contains (in its header) information about GG. When it is 0, it does not belong to any GG. 
 Joan Martínez Serra said: I understand that there is no button to create a graphic group 
 Yes, because there is nothing to be created. 
 When elements are added to (new) GG, MicroStation checks what is the highest used GG number, and set GG inforamtion in the elements to be +1 higher. So, in this aspect, GG number works as a counter. 
 As I wrote earlier, user tools to work with GG are limited, and GG information is even not displayed in Element properties dialog (but can be checked, when old key-in "analyze element" is used). 
 Joan Martínez Serra said: and "create Group" button is no a graphic group 
 You can create Named Group only. 
 With regards, 
 Jan

What is actually a "Graphic Group"?

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