How to create contour lines with photoscan ?

[quaint]

Hi everbody.

How to create contour lines with photoscan ?

Thank you ...

[tutoss]

you can't... you need a GIS software.

[Alexey Pasumansky]

Hello,

Currently contour lines extraction is not supported by PhotoScan, so I can suggest to consider the following applications: Quantum-GIS (http://www.gistutor.com/quantum-gis/19-beginner-quantum-gis-tutorials/56-how-to-generate-contours-using-raster-data-in-quantum-gis-qgis.html) or GlobalMapper (http://www.globalmapperforum.com/features/contour-lines/).

[quaint]

Thank you so much .

[quaint]

Hello,

Currently contour lines extraction is not supported by PhotoScan, so I can suggest to consider the following applications: Quantum-GIS (http://www.gistutor.com/quantum-gis/19-beginner-quantum-gis-tutorials/56-how-to-generate-contours-using-raster-data-in-quantum-gis-qgis.html) or GlobalMapper (http://www.globalmapperforum.com/features/contour-lines/).

Can i ask another question. How many laps I needed to take for 100 mt with and 6000 mt length area ( 2 or 4 )  . Its for high detail and true DEM and Contour  Lines for construction .  And do I need ground control point ? İ can  fly 50-100 mt height , I use sony nex5R and 16 mm pancake lens. DJI WKM , iosdmark2 and DJI PC ground station .

Thank you .

[stihl]

You don't need ground control points or GCP's by definition to create a 3D model like a DEM.

However if you want the DEM to have any value what so ever, you most definitely need GCP's to place it accurately relative to the world.

I suggest four lines instead of two, gives you more room for mistakes. As mentioned earlier, load the created DEM by photoscan in a GIS software which can generate contour lines from the data which you can export.

[quaint]

You don't need ground control points or GCP's by definition to create a 3D model like a DEM.

However if you want the DEM to have any value what so ever, you most definitely need GCP's to place it accurately relative to the world.

I suggest four lines instead of two, gives you more room for mistakes. As mentioned earlier, load the created DEM by photoscan in a GIS software which can generate contour lines from the data which you can export.

Thank you stihl .

[quaint]

You don't need ground control points or GCP's by definition to create a 3D model like a DEM.

However if you want the DEM to have any value what so ever, you most definitely need GCP's to place it accurately relative to the world.

I suggest four lines instead of two, gives you more room for mistakes. As mentioned earlier, load the created DEM by photoscan in a GIS software which can generate contour lines from the data which you can export.

Fly Height : 60 mt , W Overlap: %85 , H Overlap: %60

or

Fly Height : 100 mt , W Overlap:%85 , H Overlap: %75

fly times is same so

Which one best ? , Low fly height or high H Overlap ?

[stihl]

If you fly at an higher altitude your image footstamp on the ground will be larger, this means you can make less images but your model ground sampling distance (GSD) or resolution, will also be lower.

Since your need is for a DEM to generate contour lines I'd go for a high overlap. You don't need a GSD as low as 2.0-2.4 cm that you get at 60 mts. For a DEM it's most likely that you're down-sampling it anyway to 5 cm or 10 or even more before generating contour lines.
So my advice is high overlap to get the most data.

[quaint]

If you fly at an higher altitude your image footstamp on the ground will be larger, this means you can make less images but your model ground sampling distance (GSD) or resolution, will also be lower.

Since your need is for a DEM to generate contour lines I'd go for a high overlap. You don't need a GSD as low as 2.0-2.4 cm that you get at 60 mts. For a DEM it's most likely that you're down-sampling it anyway to 5 cm or 10 or even more before generating contour lines.
So my advice is high overlap to get the most data.

Thank you for the answer.

I'm not a map engineer. I'm a civil engineer.

And I wonder ,  "aerial mapping" how close to the truth? How are accepted?

[stihl]

The accuracy of the DEM depends on two factors. Image quality and how accurate your reference system is.

If you use GCP's that were measured with a regular GPS your model will have a standard deviation of several meters.
If you use RTK GPS that can go down to around 1-5cm in ideal situations.
If you use a Total Station in a referenced grid you can obtain sub centimeter results as I've gotten that myself.

[quaint]

The accuracy of the DEM depends on two factors. Image quality and how accurate your reference system is.

If you use GCP's that were measured with a regular GPS your model will have a standard deviation of several meters.
If you use RTK GPS that can go down to around 1-5cm in ideal situations.
If you use a Total Station in a referenced grid you can obtain sub centimeter results as I've gotten that myself.

I tried  it last sunday. Please look at attached pictures.

Real length 300 cm .

I checked it from orthophoto ( google earth) its about 295 cm .

No GCP ,  there is only DJI WKM Autopilots gps data . ( From IOSD MARK2 )

I think this is a good result ? But ı wonder  is there " 5 cm error on 3 meters  so is  would be 166 cm error on 100 meters ?

[stihl]

You're talking about the scale of the model now. The model's relative accuracy can be high but it's accuracy in an absolute sense, so relative to the world is most likely off as it only uses the GPS data from the DJI which has an accuracy of XY 5 meters an Z 10 meters.

Your suspicion of the error getting large as the measured length increases is correct as far as I know, hence you need GCP's that are well spread over the area.

[quaint]

Sorry my english is not good .

I understood ;

I have to use ground control points for relative to world dimensions ( measure  for 300 cm on digital model )  .

And there may be  166 cm error on 100 meters...

is it right ?

[mrafiei]

.