Inter-tidal aerial mapping - filter query

[Ranger Bob]

Hi everyone

I've been using P4D Capture and GS Pro with my I2-X4s combo for some terrestial mapping and I've had some good results back.

I now need to undertake a more difficult task out over Pole Harbour however. We need to survey the eelgrass beds at low tide in order to ascertain their condition. I imagine that a polarising filter will be required as there will still be water above them and I'll need to reduce reflections to a minimum.

It is possible to now buy a combined ND/PL filter from Polar Pro and I'm wondering if this would be a better bet than just a PL filter alone? The advantage would be that I could also use it for video to bring down the shutter speed too - but would the extra filter compromise the mapping data quality?

I'm aware that stitching water is difficult so I'm hoping to improve the success rate by utilising polarisation but I'd appreciate any advice or experience as to which filters to get; PL and ND combined or separate?

Thanks

Bob

 

[bluelight.support]

Bob - I have been lucky at just use a polarising filter normally, however Im using the X5S with Oly 12mm and that works fine for mapping grass - I use map pilot and process locally - as no cloud based service is going to give you excellent results on difficult terrain as you can't tweak as much.

 

[Ranger Bob]

Thanks for the post. The images are actually PPed in Pix4D Pro by a colleague so we do have close control that way. With a limited budget I'm torn between getting the two kinds of fiilter in one, or getting fewer single filters for the same money. My major uncertain is whether having the two in one is more convenient or whether the extra glass will cause a drop in image quality.

The choice is between the Polar Pro Vivid set and the Freewell ND & PL (3 different ND and 1 PL one) filter set - both cost £100.

Bob

 

[MrTVR]

I recently had a requirement to map a large area of Morecambe bay.

After several attempts I realised that one of the main problems was the reflections of the clouds in the wet sand. Whilst the polarising filter helped a little I found that the appearance of the sky was more influential. Go for a day with either clear blue sky and absolutely no clouds (dream on) or a grey day with continuous cloud cover. It also helped to pick a day with neap tides to keep the sand as dry as possible.

You shouldn't have as many issues if you are mapping the intertidal areas as the vegetation will help the mapping software to align the images but you may still have problems with clouds being reflected in the water.

 

[Florida Drone Supply]

Hi everyone

I've been using P4D Capture and GS Pro with my I2-X4s combo for some terrestial mapping and I've had some good results back.

I now need to undertake a more difficult task out over Pole Harbour however. We need to survey the eelgrass beds at low tide in order to ascertain their condition. I imagine that a polarising filter will be required as there will still be water above them and I'll need to reduce reflections to a minimum.

It is possible to now buy a combined ND/PL filter from Polar Pro and I'm wondering if this would be a better bet than just a PL filter alone? The advantage would be that I could also use it for video to bring down the shutter speed too - but would the extra filter compromise the mapping data quality?

I'm aware that stitching water is difficult so I'm hoping to improve the success rate by utilising polarisation but I'd appreciate any advice or experience as to which filters to get; PL and ND combined or separate?

Thanks

Bob

While having an ND filter combined with a Polarizer filter is very convenient it may not be the best for capturing the stills you are after. The ND filter will slow down the shutter speed which is not what you are looking for considering that the slower shutter speed may not create the most sharpest images and make it more difficult for proper stitching.

To answer your question, the extra ND filter could compromise your mapping data quality, to what extent you will have to judge for your self. Our suggestion is to have a couple of different density ND filters and separate polarizers for each situation depending on still photography or video. Experimentation with different filters will be the best way to figure out how to get the best results for your client.

 

[Ranger Bob]

Thank you all for your advice - looks like separate filters is the way to go. Has anyone used the Freewell set; I assume the polariser can be rotated?

I've read elsewhere that you should rotate the filter to max polarisation and then back it off a quarter turn - is this just for oblique shots where the sun is at an angle or does it hold true for nadir shots too where you are trying to reduce reflections off of water?