Problems Using Image Size and Focal Length to Calculate Camera AoV (IPVM Issue)

[john-ipvm]

@Kawboy12R and @crc2004 have brought up in a few places (e.g., Two cams with 12mm lens, but VERY different FOV. Why?) an issue with calculating HAoV from imager sizes and focal lengths.

I wanted to address the question, share some feedback and see what others have to say. I'll start first with the general problem and then into the specific issue raised.

The general problem is that manufacturer specified AoV is frequently different from what the theoretically calculation is when entering focal length (e.g., 2.8mm, 4mm, etc.) and imager size (1.3", 1./2.7", etc.).

The best way we have found to solve this is to enter in the actual AoVs from the manufacturer datasheet, e.g., we have 5,300+ (and growing every month) models in our IPVM Camera Calculator V3 While it's time consuming and costly, it provides the best solution. One key downside is that new models are always coming out and, while we are happy to add new ones in, we can't get to everyone.

Now, the specific issue with imager size calculation that @Kawboy12R has rasised . To keep it simple, historically, one just chooses a size (1.3", 1./2.7", etc.).) Problem is these are not the actual physical sizes (discussed here Image sensor format - Wikipedia). To make things more complex, imagers now have different aspect ratios and those differences will impact the potential AoV. In particular, I believe this is the issue with 1/2.7, 1/2.8, etc.

What To Do?

The solution that 90%+ of users (at least with IPVM) have done is to pick from the 5,300+ models and get the AoV listed from the manufacturer. This eliminates needing to find or enter or figure out imager sizes, etc.

Even if we address the imager size issue (and I am not sure since that depends on us tracking not only the size but the sensor model, which would increase complexity), many times the AoV of the model will be significantly different, depending on how the manufacturers uses/crops the sensor, the lens choice, etc.

My gut feel is to either remove the imager size input and focus people on either entering the model or finding the HAoV on their own or to move the imager size / focal length input to a more advanced section that explains the issues.

What do you think?

 

[mat200]

@Kawboy12R and @crc2004 have brought up in a few places (e.g., Two cams with 12mm lens, but VERY different FOV. Why?) an issue with calculating HAoV from imager sizes and focal lengths.

I wanted to address the question, share some feedback and see what others have to say. I'll start first with the general problem and then into the specific issue raised.

The general problem is that manufacturer specified AoV is frequently different from what the theoretically calculation is when entering focal length (e.g., 2.8mm, 4mm, etc.) and imager size (1.3", 1./2.7", etc.).

The best way we have found to solve this is to enter in the actual AoVs from the manufacturer datasheet, e.g., we have 5,300+ (and growing every month) models in our IPVM Camera Calculator V3 While it's time consuming and costly, it provides the best solution. One key downside is that new models are always coming out and, while we are happy to add new ones in, we can't get to everyone.

Now, the specific issue with imager size calculation that @Kawboy12R has rasised . To keep it simple, historically, one just chooses a size (1.3", 1./2.7", etc.).) Problem is these are not the actual physical sizes (discussed here Image sensor format - Wikipedia). To make things more complex, imagers now have different aspect ratios and those differences will impact the potential AoV. In particular, I believe this is the issue with 1/2.7, 1/2.8, etc.

What To Do?

The solution that 90%+ of users (at least with IPVM) have done is to pick from the 5,300+ models and get the AoV listed from the manufacturer. This eliminates needing to find or enter or figure out imager sizes, etc.

Even if we address the imager size issue (and I am not sure since that depends on us tracking not only the size but the sensor model, which would increase complexity), many times the AoV of the model will be significantly different, depending on how the manufacturers uses/crops the sensor, the lens choice, etc.

My gut feel is to either remove the imager size input and focus people on either entering the model or finding the HAoV on their own or to move the imager size / focal length input to a more advanced section that explains the issues.

What do you think?

HI John,

I would like to see the user interface easier - and thus the picking the model would be a good first option.

Perhaps making a clear to notice check box which enables the ability to enter advanced / custom settings would work.

 

[john-ipvm]

I would like to see the user interface easier - and thus the picking the model would be a good first option.

Matt, thanks. How you would you like it to be easier? In terms of 'good first option', would you like the model selection display to be shown immediately? As a point of reference, 60% of cameras saved in the Calculator have models, so it's clearly the majority use case and would be even higher if we made that easier / automatic. Let me know.

 

[mat200]

Matt, thanks. How you would you like it to be easier? In terms of 'good first option', would you like the model selection display to be shown immediately? As a point of reference, 60% of cameras saved in the Calculator have models, so it's clearly the majority use case and would be even higher if we made that easier / automatic. Let me know.

Hi John,

Model selection should be one of the first options people see imho.

To account for "models" not listed, you have have some of the more common settings available in the model selection:

Say "Generic 1080p 90 degree H FOV ... " or something along those lines to help people get a close enough estimated view.

 

[Fastb]

John,

I tried finding my camera in the list of cameras in the camera calculator. I searched for IPC-HFW5231E-Z.
No match.
But much later, after I posted my question (Two cams with 12mm lens, but VERY different FOV. Why?)
and while digesting answers, I found a similar cam was posted, ie: IPC-HDW5231R-Z.
Possibly the only difference between the two is the form factor of the housing, and not the lens, sensor, optics, etc.
If so, maybe IPVM could support a more expansive "search" of the camera list. As google does, when a search will list exact matches, and near matches.

I offer this as an answer to your question of "How you would you like it to be easier?"

Fastb

 

[framednlv]

John,
I've read you post and ran across the other thread that mentions the inaccuracy. I have used your calculator.ipvm.com and always assumed the numbers could vary, even with the same model camera. I think if you just put some disclaimers (footnote or *) next to the calculation that might be off, that would be fine with me. It would be nice to know how much variation there could be in the calculations (IE, 2.8mm ~ 86-90deg or 88deg ~ 2.5~3.0mm). For the most part as an end user, I have a choice of lens but no clue what the angle of view is (horizontal). With the angle of view it's not to hard to figure out the PPF numbers at any given distance, jut hard to figure out what the lens size should be for a given angle.

Me thoughts,
Chris

 

[Kawboy12R]

Thanks for your response John. I got in the habit of not choosing listed models when nearly all of the cameras I tried to choose weren't available as options. Admittedly, these tended to not be North American models that professional installers wouldn't be installing. I then ran into the problem that the real world AoV shown by an actual camera didn't quite match up to what the calculator was projecting onto the map, sometimes amounting to almost the difference between a 6 and 4 mm lens. No big deal- I know that published camera specs are often wrong and doublechecking a Swiss Army knife tool like yours against everything is impossible.

I guess the best answer is to either buy varifocal cameras where the desired PPF or AoV is definitely within the range of the camera, or buy a sample of each camera you intend to install, and compare the real world view against the calculator and juggle the lens length, if needed, to match things perfectly in case of discrepancy. It's really not fair for all blame to be assigned to your calculator. It is a really good tool but, like all tools, shouldn't be used blindly. Or by the blind. It reminds me of an old adage- trust, but verify.

One of my first jobs as a student was working for a research scientist. It puzzled me at first why he would calculate things three ways- with a computer program, with a calculator, and by hand. Only after all three ways matched was something fit to publish.

As for making the calculator easier to use, I find it easier to go by imager and lens length than imager and HFoV, but adding both options for models in the database would probably make things more confusing. Having more of the cheap Chinese model numbers for Dahua and Hikvision cams in the listing would certainly help out many of the members here.

 

[john-ipvm]

I got in the habit of not choosing listed models when nearly all of the cameras I tried to choose weren't available as options. Admittedly, these tended to not be North American models that professional installers wouldn't be installing.

Just tell us what those models/series are. That's what we've asked here What camera models do you want added to the IPVM Calculator?
If you tell us the models / series, we will add them in this week.

As for making the calculator easier to use, I find it easier to go by imager and lens length than imager and HFoV

Clarification: If you know the HFoV, you do not need to know the imager size at all. Imager size is only used when all you have is the focal length of the lens, and thereby need to estimate the HFoV.

One other thing that is coming out by next week that should help here is a revamped camera model selector, including a simpler way to immediately request models not included to be added. Right now, you have to manually go to the contact page, etc. With this change, it will include a link at the bottom of the page when a model is not found, that prepopulates that model name/number, allowing you to directly request it.

 

[john-ipvm]

Update: We released an upgraded version of the IPVM Camera Calculator V3 In it, we hide imager size and focal length by default and added a number of features to make it easier to use camera models, see release description - Calculator - NEW Advanced Searching, Camera Favorites, Model Adding Any questions or feedback, let me know.