Hello all, I seem to be having an issue with the DEM while planning a photogrammetry mission.

When planning a photogrammetry mission today it seemed to be giving me a strange terrain following solution when using 0, 90, 180, 270 or anything close to those numbers for the "direction angle". If I choose 45 degrees (or something far away from the 4 main compass points) it gives a much better flight plan with good terrain following but if I choose 0, 90, 180, 270 etc.. degrees it will give a very low resolution flight plan and I think from looking at the area on google earth would actually cause me to crash into the terrain (I am flying very low to the ground the whole time). The flight plan when using 0 degrees looks more like a 100 meter grid than a nice terrain following flight.

I don't remember having this problem before but I haven't used UGCS for a 8 months or so so I'm not sure if this is a bug in the latest update. I'm pretty sure when I did jobs in the same area last year I didn't get this issue.

In the attached files/ screenshots all parameters are exactly the same except for the "direction angle".

Any help would be greatly appreciated.

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Replies to This Discussion

Hi Robert,

could you save your mission to file (xml) and post it here or send to our support? It's hard to understand what is wrong here having screenshots only.

Thanks Alexey, mission file attached here.


Robert, I still don't see issues with this mission. 

This is elevation profile with directional angle 45 for route NE1

and for directional angle = 0

and last route is more optimal - less waypoints and flight time

Hi Alexey,

I agree the 0 degree is a far better flight path for many reasons but I'm concerned that it isn't following the terrain very well. I don't think the elevation profile has enough resolution to really see if it's actually following the real terrain well enough. If you look at the actual drawn parallel lines over the survey area you'll see that when they are orientated at 0 degrees there is a very obvious "grid" i.e. lines of way-points where there is a change in the planned elevation. I initially though this was just the resolution of the DEM in that area (at about 100m grids) but when I moved the course direction to 45 degrees it follows the terrain much more accurately and with a much higher resolution DEM. You can clearly see on the parallel lines that it follows gully's and spurs much more accurately when using 45 degrees compared to 0 degrees. As I said, I'm sure this wasn't the same last year when I planned and flew similar missions, all using 0 degrees as the course direction.

Hi Alexey,

I have gone back and found last years flight plans and it seems to do the same thing so that means this isn't a new issue, it's just that I didn't notice it as the areas were broken into smaller parts so it wasn't as obvious, sorry for misleading you there. I still believe it to be a bug but maybe it's only one that occurs when you are planning flight that require ultra high resolution (2.6mm per pixel).

I would like to import a high res DEM (1 arc second, not that high res but the best I'll be able to get) to see if it makes a difference but I'm reluctant to buy the PRO version just to find it doesn't work or make a difference. I'm more than happy to pay for the Pro version if it does work though. What is the refund policy? If I buy the PRO version and find the DEM UGCS currently uses is the same as the best one I can find online will I be able to get a refund? Am I able to find out the resolution of the DEM in the area I need to work to see if upgrading will make a difference?

I'm not able to do a flight first to create my own DEM as we get helicoptered into the site and only have a short amount of time to get as much of the area covered as possible.


Hi Robert,
in latest versions we introduced new Photogrammetry tool parameter called AGL tolerance. If you will reduce it from your current 1m to say 0.5 meters you will get lot of additional waypoints and better terrain following.
May be this is reason of differences between routes generated in old and current UgCS versions.
Also I see (in NE 1 route) that with directional angle = 0 flight lines will be aligned with terrain slope (up and down). In case of 45 degrees it will be necessary to generate additional waypoints to get same AGL tolerance.

BTW, you can buy UgCS Pro from our site and if you will be unhappy we will rollback PayPal transaction. Just drop us message during 2 weeks after purchase.

Please note that UgCS Pro has same DEM data as Open or One versions out of the box. Main difference that UgCS Pro allows you to import your DEM data. 

Thank Alexey for all your help.

Do you know what DEM resolution UGCS uses for the area that mission is in? is there a way to find out? I can download a 1 arcsecond (about 30m x 30m) resolution DEM but there is no point if it is already using that one. I think it looks to be using a 3 arcsecond (90 x 90m) DEM but not 100% sure.


You are right, we have data with 3 arc second resolution out of the box. So if you have 1 arc second or better data you can benefit from UgCS Pro.

You can see how to import DEM data here - https://youtu.be/CLDeXy4pUXI ;

That's great, thank you so much for the support and knowledge. Great software with great support is hard to find. 


Thank you Robert. Do not hesitate to ask us in case of any questions/problems.



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