Accuracy of shadows - daylight saving

[iankids]

Hi All,

In a current application before council, the officer noted that the 3pm shadow did not look correct and was probably closer to 2pm than 3pm.

I went through and checked everything in the model - true north - shadow setting etc and all seemed OK.

I was about to go into panic mode and fire off a support request when I thought to check if the tick box for daylight saving was activated. It was. Unchecking it brought everything back to display correctly.

The info in the help on this is a bit ambiguous.

It says: 4. If you want shadows to reflect daylight savings time for the specified location, select Automatically adjust clock for daylight savings changes.


When I had read it before setting the daylight saving switch I had taken this to mean that Revit would adjust to daylight saving time much as the clocks within Windows do when you get to the appropriate date for which ever city you are in. It would appear that this isn't the case and this tick box simply moves the time frame one hour regardless of date when the shadows are set for.

In Melbourne, we typically provide shadows for the equinox (22nd September) which is well before the daylight saving kicks in. Thus, because I had the "daylight saving" box ticked, Revit had indeed moved the shadows one hour and the 3pm shadows was in fact displaying a 2pm setting.

Cheers,


Ian

[cporter.207875]

That's quite an eye to be able to pinpoint such a minor difference in shadow length.

[Alex Page]

I would seriously suggest you tell Autodesk this - surely their implementation is wrong....this really worries me since we use this tool as part of our council obligations all the time and Ive got a feeling we've made the same logic mistake as you have

[PaulB]

I think the problem may be in that, not every project will be in your state or time zone so I'm not sure if it would work.

Just a quick thought.

[iankids]

I would seriously suggest you tell Autodesk this - surely their implementation is wrong....this really worries me since we use this tool as part of our council obligations all the time and Ive got a feeling we've made the same logic mistake as you have

I will advise Autodesk & let you know any response. At a minimum, I think the help should be re-written to ensure greater clarity.

I think the problem may be in that, not every project will be in your state or time zone so I'm not sure if it would work.

Just a quick thought.

In terms of how I thought it worked, there was no logical problem of you being in one state and the job in another. The job location is set internally and thus the daylight saving calculation was an internal one. Now, as I more fully understand that it doesn't work that way, I can certainly see some complications which would arise. Again, I think the only real problem here is the current description in the help is poorly worded and open to the misinterpretation I placed on it.

I would have thought that a more straight forward description such as "By activating the daylight saving function you will adjust the internal clock for this shadow diagram by one hour. Other shadows will not be changed. Doesn't sound as sexy as "it will automatically adjust for daylight saving time," but I would have understood it!

Ian

[trombe]

I would seriously suggest you tell Autodesk this - surely their implementation is wrong....this really worries me since we use this tool as part of our council obligations all the time and Ive got a feeling we've made the same logic mistake as you have

Yo Alex.
hope you are well.
If you need some baseline, almost bullet proof (sorry bulletproof design for the liberty here !!) evidence of where things ought to be at, I have 2 x A1 hard copy sheets of the full sun path for the year in 2 halves, by AR Houghton, structural Engineer, on contract to the WCC in 1994.
If you feel you want to check Revit against hand generated data , e-mail me off line and I can arrange it. Basically, no WCC officer can go against the docs as they are their own in house records.
Actually none of them know they have it ! which is even better !.
I have used them to check Revit and have quoted the documents in RC applications.
Up to you.
Roger Walkers office took a copy 3 years ago.
regards
trombe

[petebalf]

So Ian,
if I have this right, the only time you would switch this button on would be for a sun study that is designed to show a sunpath that exists within the calendar range of when daylight savings happens. A completely manual operation that purely replicates us moving it manually one hour to compensate.
After thought, It can't be automatic as states are often adjusting the start of daylight saving from one year to the next, so it couldn't just rely upon a set date every year to change itself.
peter

[iankids]

So Ian,
if I have this right, the only time you would switch this button on would be for a sun study that is designed to show a sunpath that exists within the calendar range of when daylight savings happens. A completely manual operation that purely replicates us moving it manually one hour to compensate.
After thought, It can't be automatic as states are often adjusting the start of daylight saving from one year to the next, so it couldn't just rely upon a set date every year to change itself.
peter

Yep, That's pretty much it.

If council asks for summer solstice shadows (or for some other time after daylight saving has commenced), then one would tick the box in that instance, but otherwise it should remain unticked.

Ian

[petebalf]

Thanks Ian,
I learn a new thing every day.
I'll mention it in my next class to my students.

peter

[Alex Page]

On a similar topic - we have an office in anouther country (Australia) and we help them out from our office here (New Zealand) - very rudimentry, basically move the central file over here for a week and then move it back.

The nasty thing is that NZ is two hours ahead of Australia and the "Sun and Shadow" settings automatically change the time to 2 hours behind!! The project location is still correct thou so if we do the Sun and Shadow diagrams here they are completely out - so we have to rely on our NZ reviteers remembering to change the time and also the Aussie reviteers have to remember to change the time again!