Animation: expression inside scale

[Necolatis]

I cannot seem to get expression inside scale to work. This scales to zero all the time it seems:

Any help appreciated.

Code: Select all

<animation>
    <type>scale</type>
    <object-name>LightBeaconGlow</object-name>
    <expression>
      <dif>
        <property>sim/time/sun-angle-rad</property>
        <value>1</value>
      </dif>
    </expression>
    <x-min>0.0</x-min>
    <y-min>0.0</y-min>
    <z-min>0.0</z-min>
    <x-factor>5.00</x-factor>
    <y-factor>5.00</y-factor>
    <z-factor>5.00</z-factor>
  </animation>

System:
Win7, FG 3.3

[onox]

You wrote <dif> instead of <diff>. See if that fixes it.

[Necolatis]

It does not help, also the wiki say dif, not diff: http://wiki.flightgear.org/Expressions

Same problem in 3.2, also tried with <difference>.

[Necolatis]

I just searched through all aircraft in $FGDATA, none seems to be using expressions in animations.

I have made a bug-report: https://code.google.com/p/flightgear-bu ... il?id=1619

[Thorsten]

Not sure this is intended to be supported everywhere - but you sure could make a property rule which computes whatever you need to a second property and use that in the animation.

[Necolatis]

I got a reply to the bugreport, which solves it:

You must supply a <property> entry for scale, given that your <property> is not defined it's not surprising you get a 0 scaled result.
You can use your expression in the <factor> or <offset> inputs.

Documentation in $FG_ROOT/Docs/model-howto.html#scale is pretty clear about this.

If you don't need to apply different factors/offsets on the axes you can use <factor>/<offset>.

[Necolatis]

Updated the wiki to reflect this.

[Johan G]

I wonder if that applies to using expressions in the other types of animations as well?

Too bad that it seems that the use of <property> is explicit in model-howto.html, but that you have to use any expression in either or both of <factor> and <offset> is implicit. Sometimes it is a good idea to explain the "obvious", as it may not be that to someone else. (In fact for FG 3.0.0 "expression" is only mentioned in relation to the <condition> tag, in essence for boolean expressions, and there is no separate document on expressions.)

[Necolatis]

Actually I tested expressions inside offset, could not get it to work.

I am not convinced expressions inside animations, is not broken.

[fursanton]

also need mention that you can't use <factor> and <offset> if you're using <expression>. You should use <product> and <sum> elements inside <expression> tag.

[Octal450]

Three years later

[mhab]

I try to add a similar question as I can't seem to get <expression> to work within scale animation ...

I want to shrink the object in z direction depending on the location of the elevator.
If I try the following it basically works

Code: Select all

  <animation>
    <type>scale</type>
    <object-name>elev-4-wires</object-name>
    <property>surface-positions/elevator[3]/position-norm</property>
    <center>
      <x-m> 0.00</x-m>
      <y-m> 0.00</y-m>
      <z-m>19.00</z-m>
    </center>
    <x-min>1.0</x-min>
    <y-min>1.0</y-min>
    <z-min>0.1</z-min>
    <x-factor>1.0</x-factor>
    <y-factor>1.0</y-factor>
    <z-factor>1.0</z-factor>
  </animation>


Problem is: I need to invert the scaling so it follows 1-"the-property-used".

I tried the following without success:

Code: Select all

  <animation>
    <type>scale</type>
    <object-name>elev-4-wires</object-name>
    <property>surface-positions/elevator[3]/position-norm</property>
    <center>
      <x-m> 0.00</x-m>
      <y-m> 0.00</y-m>
      <z-m>19.00</z-m>
    </center>
    <x-min>1.0</x-min>
    <y-min>1.0</y-min>
    <z-min>0.1</z-min>
    <x-factor>1.0</x-factor>
    <y-factor>1.0</y-factor>
    <z-factor>
      <expression>
        <dif>
          <value>1.0</value>
          <property>surface-positions/elevator[3]/position-norm</property>
        </dif>
      </expression>
     </z-factor>
  </animation>


The Wiki and all other mentioned sources of information are not really helpful for me yet ...

Any advice ?
Mike-DE

[Octal450]

Put this expression in a gain filter with a gain of 1, then use the output for the property.
See PropertyRules on the wiki.

Kind Regards,
Josh

[mhab]

Thanks for the hint.

Considering all this, and the fact that I am using this for a carrier, which in turn is used as an AI model, I handle a new property in the Nasal main-loop of the carrier.
It works now as desired and adds a nice feature. The carrier elevators on the new Truman carrier do not work in "free fall manner" but have wires which follow the movement of the carrier.

Mike-DE

[Octal450]

Welcome, anytime.

Kind Regards,
Josh