Model Size Increase With Reduced Elements

[Dale.Bartlett]

Hi All, I posted the below to the Revit Architecture forum, but before anyone blasts me for double-posting or non-api posts: This is pertinent to the addin I am developing, and I thought a developer's take on the geometry question would be relevant to other projects in this forum. Additionally, I had no  replies so please indulge me.

I have an issue where we have a tunnel model comprising 1600 ring segments. Each segment is assembled from 6 part rings to form a full 360 degree ring. In an effort to reduce the file size and the number of elements, I changed the ring segment from 6 parts to one. As this reduced the total elements from 9600 to 1600, I naturally expected a reduction in file size. The file size actually increased from 220MB to 411MB. Other than the change to the profile defining the segment sweep, all else is unchanged. The surplus part segments have been deleted, no warnings, no annotation, no sheets, saved as new file, not a central file, purged, compacted, no imports, no links, no groups, no arrays. The revised ring segment family is clean, small, purged (500KB). Does anyone have detailed knowledge of the underlying geometry definitions that may have such an effect? Thoughts? Many thanks and Happy New Year. Dale

[Dale.Bartlett]

Update:

Copy-Paste geometry had no effect. However: As the segments were built as a Swept Blend, and the start and end profiles were the same, I revised the geometry to a Sweep with a two concentric circle profile. The file reduced from 411MB to 18MB. This I can understand, however I remain puzzled as to why reducing the model count to 1/6th resulted in a doubling of the file size. Anyway immediate problem solved; let's all move on. Dale 

[jeremytammik]

Dear Dale,

Happy New Year!

Thank you for your interesting query and congratulations on finding such an impressively effective solution.

I agree that this sounds weird.

I forwarded it to the development team and will keep you updated as to what they say.

Is there any way that you could provide me with the various models that you generated, or alternatively some minimal fool-proof code to generate them programmatically? Without those, there is very little the development team can say. Thank you!

Best regards,

Jeremy

[jeremytammik]

Dear Dale,

Would you like to provide the sample models for the development team to take a look at?

Thank you!

Cheers,

Jeremy

[Dale.Bartlett]

Hi Jeremy,

Thanks for following up. I created two sample models for your team's investigation. The files have been stripped, but nevertheless the material is still considered confidential, so I will send a dropbox link to you privately. The ring on the left comprises 6 swept blends and generates the smaller model. The ring on the right is a single swept blend with the profile comprising an inner and outer circle joined through a 2mm gap at the bottom. Note, swept blends require a single profile, whereas a sweep could use two concentric circles. The segments are then assembled via the API. The samples provided each comprise 420 elements. The 6 part version = 136MB and the 1 part version = 250MB. Any feedback would be appreciated. Thanks, Dale. 

[jeremytammik]

Dear Dale,

Thank you for the sample files.

I downloaded them from Dropbox and submitted a request for the development team to take a closer look. I am now in the process of uploading the sample files to that case.

I logged the issue REVIT-84188 [Model Size Increase With Reduced Elements -- 11375355] with our development team for this on your behalf as it requires further exploration and possibly a modification to our software. Please make a note of this number for future reference.

You are welcome to request an update on the status of this issue or to provide us with additional information at any time by submitting a new case through DevHelp Online quoting the change request number or this case number.

This issue is important to me. What can I do to help?

This issue needs to be assessed by our engineering team, and prioritised against all of the other outstanding change requests. Any information that you can provide to influence this assessment will help. Please provide the following where possible:

• Impact on your application and/or your development.
• The number of users affected.
• The potential revenue impact to you.
• The potential revenue impact to Autodesk.
• Realistic timescale over which a fix would help you.
• In the case of a request for a new feature or a feature enhancement, please also provide detailed Use cases for the workflows that this change would address.

This information is extremely important. Our engineering team have limited resources, and so must focus their efforts on the highest impact items. We do understand that this will cause you delays and affect your development planning, and we appreciate your cooperation and patience.

Thank you!

Cheers,

Jeremy

[jeremytammik]

Dear Dale,

Apparently, two issues were accidentally logged for your case.

The development team closed the issue REVIT-84188 [Model Size Increase With Reduced Elements -- 11375355] that I intentionally logged with them as a duplicate.

They are now looking at the duplicate issue REVIT-84187 [Model Size Increase With Reduced Elements -- 11375355] instead.

Please make a note of this number for future reference.

Sorry for the hiccup. Hopefully no confusion will ensue.

Cheers,

Jeremy

[Aaron.Lu]

Dear Dale,

A quick update: we've confirmed it is a bug, but need more time to investigate.

[jeremytammik · Accepted solution]

Dear Aaron,

Thank you very much for your accurate and succinct summary of the facts.

Dear Dale,

In case you are interested in more details, as you might well be, since you spent some time and effort researching them yoursefl, here they are:

The development team analysed the issue REVIT-84187 [Model Size Increase With Reduced Elements -- 11375355] and say:

Observations:

(1) There are two types of element rings: (a) StraightElementRing (b) LeftCurveElementRing.

The six part version has 80 StraightElementRings and a lot more LeftCurveElementRings.

The one part version has 79 StraightElementRings and a lot more LeftCurveElementRings.

(2) Geometry sizes of the element rings: Please see the attached BRep Geometry dump files of one element of each type for the one part and six part versions.

For the StraightElementRing, the difference in sizes of the geometry dumps are as expected - one part version is less than the six part version.

For the LeftCurveElementRing, the sizes of the geometry geometry dumps are NOT as expected - one part version is BIGGER than the six part version.

Explanation for the unexpected size difference: The one part version of the LeftCurveElementRing has the two curved surfaces represented by Hermite surfaces consisting of 1089 point nodes totaling 2178 point nodes. In the six part version, the curved surfaces are represented by 12 Hermite surfaces of 81 point nodes each and 12 Hermite surfaces of 4 point nodes each, totaling 1020 point nodes.

I think this explains the unexpected behavior - why the one part version has larger file size than the six part version.

One more observation: The number of elements in both of the versions seem to be the same. Only the element geometries have different numbers of faces.

We will investigate further to see why the geometry size of the one part version of a curved ring is more than that of the six part version.

Cheers,

Jeremy