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Messages - Dave Martin

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General / Re: coordinate system
« on: January 19, 2019, 02:40:55 PM »

Have you looked in the PhotoScan/Metashape manual - lots of info in there.


I think you can get a long way using the approach you suggest. What I would suggest is that, if you know the bulk surface is flat, the control points you create, assign them relatively tight accuracy in Z but specify low accuracy (high error margin) in X and Y - that way it should pull the surface flat but not introduce any lateral distortion.


General / Re: after Merge with Markers difference in hight
« on: January 19, 2019, 01:07:13 PM »
Leonid - how were the individual chunks geo-referenced?  and how were your images acquired?  by a DJI product?

General / Re: Export of contours linked with NDVI data (for GIS analysis)
« on: January 18, 2019, 02:58:12 PM »

NDVI preparation and export is described in quite good detail in the manual. NDVI export is on page 43 of the current manual.


General / Re: Help with Salvaging a Dense Cloud
« on: January 18, 2019, 02:50:18 PM »
Gross - thanks for updating, always good to hear - too many times folk on the forum suggest a response and never hear anything back.

General / Re: Agisoft Photoscan: Medium vs Ultra High
« on: January 06, 2019, 02:32:47 PM »

Given the subject, rather than asking here in the 'General' section of the forum, you might (also) try asking in the dedicated 'Face and Body Scanning' section as well.


General / Re: Export DEM to Litchi
« on: January 05, 2019, 12:36:01 AM »
So what WGS84 co-ordinates do you expect to see? i.e. what is the position of the Lower Left corner of your DEM?


General / Re: Help with Salvaging a Dense Cloud
« on: January 04, 2019, 01:30:39 AM »

Height differences are an endemic issue with DJI - have a search on here for threads on DJI height (or Z) issues, you'll find lots including advice on how to rectify.


General / Re: Multiple camera rig. What to buy?
« on: December 19, 2018, 05:20:45 PM »

You might also get more answers if, rather than here in the 'General' section of the forum, you ask in the dedicated 'Face and Body Scanning' section as they mostly use multi-camera rigs.


Apavlicek - I don't use DJI for photogrammetry, but I know there is a well-known issue with the elevation stored by DJI, it is the height above takeoff. Have a search on here of 'DJI height' and you'll find plenty of threads and fixes.


General / Re: DEM without geographical coordinates
« on: December 18, 2018, 02:27:30 PM »
Hi Frans80,

Just a quick comment - you mention that your goal is compute the standard deviation of the height of the soil. Unless the surface is extremely varied, GPS co-ordinates are going to be too crude - but I think you will need some sort of reference. In the post you quoted, it does mention the key phrase "the scale of the resulting DEM will be arbitrary" - so you end up with more of a qualitative than quantitative result.

I think you will need some way of scale into your model - otherwise the resultant DEM etc. are unit-less. Without input of any absolute scale, your model may be internally consistent, and you could perhaps compare the height SD in different zones of the same DEM and say 'area A is twice as rough as area B' - but you could not compare between projects or give any meaningful figures. Without scale, you could have a DEM of soil with height variations of a few millimetres, or an aerial of the Alps with height variations of hundreds or thousands of metres.

I think you may well find you need to capture some object or points of known scale to make the most of your project.


General / Re: markers won't be detected
« on: December 14, 2018, 05:18:14 PM »
Micha - I think the reason only the 'unsharp' are detected is because they are some of the smallest.  I think the other targets may be too big for the automatic target detection to work, If you search on here for Target Detection Failure, you can find a number of threads on this subject, including this one on exactly the same subject, in which Agisoft advise that the central black circle should occupy no more that 70 pixel diameter.

(I would also suggest that you increase the depth of field in your photographs, it looks like everything is locked to the nearest edge of your base; also try and get the frame better filled with your subject - I guess the cup only occupies 5 - 10% of the frame.)


General / Re: Copy camera location/info to new image
« on: November 30, 2018, 04:13:45 PM »

It is much easier - provided the images have same names (one folder with pattern, one without) you can just change to point to the alternative images before making your texture.

Just search here for 'change image path' - e.g. one thread from a few weeks ago on exactly the same subject:


General / Re: white balance off on textures
« on: November 11, 2018, 06:00:41 PM »
Hi Morgan, 'capture1' is the model, so is 'capture2' one of the initial images?  If so, is that before it goes into PhotoScan? or is it after you click on one of the imported photos in the gallery in PhotoScan?


General / Re: Wgs84 to osgb36 conversion is wrong
« on: November 07, 2018, 12:55:17 PM »
Hi John,

I was pretty sure recent PhotoScan was using OS TN/GM 02, but as I don't have PhotoScan workstation to hand I can't confirm.

Where are you seeing the discrepancy - is it an on-screen tabular WGS84 and OSGB for the same GCP or check point? or is it when you go to get the coordinates from a point on a DEM?


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