How to read STEP color properly as CAD Assistant

Pavel Chmelar
Tue, 10/03/2023 - 16:24

Forums:

Dear OCCT community,
when I use CAD assistant to read a STEP file and I open material manager I see this:

When I read color by using XCAFDoc_ColorTool as colorReader->GetColor(label, XCAFDoc_ColorSurf, color) I will get color circled as blue #101603FF, which is too dark .
How should I read color in different way to get the correct one, circled as red #495421 .

Thank you for help.

Best Regards
Pavel Chmelar

Dmitrii Pasukhin
Thu, 10/05/2023 - 00:16

Hello, which version of OCCT do you use? CAD Assistent use the same color system as native OCCT XCAF.

Best regards, Dmitrii.

Pavel Chmelar
Thu, 10/05/2023 - 10:53

Hello, I'm using the latest version 7.7.2.
I've found this lesson on Quaoar and it seems that I need to iterate also through faces, because this model (see the attachment) in CAD Assistant:

I reading as:

When I go through assembly I reading only the blue part of a wheel (oposit side of wheels is not visible because of normals, when I rotate the model all four wheels are visible). The red part is missing.

Best Regards
Pavel

Attachments:

chassis.zip

gkv311 n
Thu, 10/05/2023 - 11:01

The first color hex name is generated by XCAFDoc_ColorTool::AddColor() method and the second one - by Quantity_ColorRGBA::ColorToHex(). The second method converts color from linear to non-linear sRGB color space, while the first one converts values to hex directly, which is wrong. I think it is a bug in XCAFDoc_ColorTool::AddColor().

    //! Returns hex sRGBA string in format "#RRGGBBAA".
    static TCollection_AsciiString ColorToHex (const Quantity_ColorRGBA& theColor,
                                               const bool theToPrefixHash = true)
    {
      NCollection_Vec4<Standard_ShortReal> anSRgb = Convert_LinearRGB_To_sRGB ((NCollection_Vec4<Standard_ShortReal> )theColor);
      NCollection_Vec4<Standard_Integer> anSRgbInt (anSRgb * 255.0f + NCollection_Vec4<Standard_ShortReal> (0.5f));
      char aBuff[12];
      Sprintf (aBuff, theToPrefixHash ? "#%02X%02X%02X%02X" : "%02X%02X%02X%02X",
               anSRgbInt.r(), anSRgbInt.g(), anSRgbInt.b(), anSRgbInt.a());
      return aBuff;
    }

Pavel Chmelar
Wed, 10/25/2023 - 09:23

Thank you very much @gkv311 n. It's exactly this reason why the color was wrong.

To my post above. The model wasn't complete because I didn't expected that a top shape itself with some sub-shapes contains also space data.

Best Regards
Pavel

Josep Fontdecab...
Mon, 11/13/2023 - 19:27

Hi
I am quite new here. I am using version 7.7.0 to read STEP files.
I can't get the color from a STEP file generated by SolidWorks with all COLOUR_RGB labels apparently in place.
I try the standard:
Handle(XCAFDoc_ColorTool) ColorTool = XCAFDoc_DocumentTool::ColorTool(mainLabel);
Quantity_Color color;
Standard_Boolean ok = ColorTool->GetColor(label, XCAFDoc_ColorSurf, color);
It always returns false.
Should I move to 7.7.2 ? Where can I download it ?
Or do I need colors saved by SW in a particular manner ?
Thanks in advance

Dmitrii Pasukhin
Mon, 11/13/2023 - 23:06

label should contains a color? 7.7.2 have no updates about color extractions

Best regards, Dmitrii.

Josep Fontdecab...
Wed, 11/15/2023 - 22:37

Dimitrii
Forgive my poor background on STEP format. I just dropped here a week ago.
I understand every shape is associated to a label, and there is entities that are descendents of either. I am trying to find what descendent entities they have so I can find the one containing color information.
I was trying to follow the tree structure so I can see what information is associated to every shape. I am trying to build a small STEP->to->STL converter and add relevant information to the STL header for every shape I find.
Any help on that direction will be appreciated.
Thanks in advance.
Josep