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Question

In need of igds_rotation clarification.

drejkzet

Hello everyone.

I am storing dgn v8 files into postgis database and I am getting confused by igds_rotation attribute.

I know what it represents, however the value itself is the part I do not understand. Browsing through documentation I get that

"The rotation is measured in degrees counterclockwise up from horizontal"

and

"Range: -360.0..360.0"

 

Which basically means (correct me if I am wrong) that counterclockwise rotation is [0,360] and clockwise rotation is [0, -360].

I need rotation to always be > 0, therefore I need to normalise the value.

Now, I want to convert for example -60° to 300°, which is basically adding 360 to negative angle value.

When I inspect the features, I see that the correct rotation behavior is when I add 180 to fme_rotation, not 360 which is not what I would expect.

Can someone please explain why FME behaves this way (FME 2017.0). or am I just missing something?

Thanks in advance,

Radek

5 replies

L
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Hi @drejkzet

are you working with texts? It looks like the igds_rotation description is a bit confusing. In Microstation, the rotation angles are indeed measured from horizontal, i.e. a line placed with Angle = 0 is a horizontal line. However, a text with Angle = 0 is a not rotated text, i.e. an upright text. This makes sense if you think about the text insert point and its vector.

The +360 vs. +180... what is the correct behaviour that you expect? Could you maybe share a screenshot with some geometries and notes regarding what you get vs. what you expect?

drejkzet
  • drejkzet
  • Author
  • April 12, 2018
lenaatsafe wrote:

Hi @drejkzet

are you working with texts? It looks like the igds_rotation description is a bit confusing. In Microstation, the rotation angles are indeed measured from horizontal, i.e. a line placed with Angle = 0 is a horizontal line. However, a text with Angle = 0 is a not rotated text, i.e. an upright text. This makes sense if you think about the text insert point and its vector.

The +360 vs. +180... what is the correct behaviour that you expect? Could you maybe share a screenshot with some geometries and notes regarding what you get vs. what you expect?

Hello. What I expect is, if I have -60° rotation, after I add 360° to that rotation, I expect to get 300°. If I do this calculation on a regular attribute, I get this value just fine, however when I try this math in fme_rotation or igds_rotation attribute, it suddenly behaves differently (as you can see in those two screenshots I have posted) - I have to add 180° and not 360° to get the positive angle value.

 

 

L
Forum|alt.badge.img
drejkzet wrote:
Hello. What I expect is, if I have -60° rotation, after I add 360° to that rotation, I expect to get 300°. If I do this calculation on a regular attribute, I get this value just fine, however when I try this math in fme_rotation or igds_rotation attribute, it suddenly behaves differently (as you can see in those two screenshots I have posted) - I have to add 180° and not 360° to get the positive angle value.

 

 

Could you please post a screenshot where we would see the original igds_rotation and the calcuated one (with e.g. 360 added)?

 

 

L
Forum|alt.badge.img
  • lenaatsafe
  • September 13, 2018
Hi @drejkzet

 

one of our lead developers noticed this discussion and explained to me what was happening with your data.

 

Apparently, igds_rotation is an alias for fme_rotation. I.e. in step 3 and 4 you add 180 and then another 180 to the same value. This is why at the end both - fme_rotation and igds_rotation - are equal to test2 and not test1 as we both expected.

 

How would you know that igds_rotation is an alias for fme_rotation? You can't see this easily in Data Inspector. However, if you log the feature, the log will provide some helpful additional info:

 

 

To log the feature please either use Logger in your workspace or select the feature in Data Inspector and RightClick on it in Feature Info panel > Log Feature Information.

 

I hope this solves the mystery.

 

 

 

L
Forum|alt.badge.img
  • lenaatsafe
  • September 13, 2018
drejkzet wrote:
Hello. What I expect is, if I have -60° rotation, after I add 360° to that rotation, I expect to get 300°. If I do this calculation on a regular attribute, I get this value just fine, however when I try this math in fme_rotation or igds_rotation attribute, it suddenly behaves differently (as you can see in those two screenshots I have posted) - I have to add 180° and not 360° to get the positive angle value.

 

 

Hi @drejkzet

 

one of our lead developers noticed this discussion and explained to me what was happening with your data.

 

Apparently, igds_rotation is an alias for fme_rotation. I.e. in step 3 and 4 you add 180 and then another 180 to the same value. This is why at the end both - fme_rotation and igds_rotation - are equal to test2 and not test1 as we both expected.

 

How would you know that igds_rotation is an alias for fme_rotation? You can't see this easily in Data Inspector. However, if you log the feature, the log will provide some helpful additional info:

 

 

To log the feature please either use Logger in your workspace or select the feature in Data Inspector and RightClick on it in Feature Info panel > Log Feature Information.

 

I hope this solves the mystery.

 

 

 

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