Contour Lines using the DTM

Contour lines are lines connecting points of equal elevation. They are useful because they allow to better understand the shape of the land surface (the topography) on a map.


The Elevation Interval of a contour map is the difference in elevation between successive contour lines. Typical values of the Elevation Interval are 100, 50, 25, or 10 meters for areas with large elevation variations (e.g. mountains) and 5, 2, 1, or 0.5 meters for areas with small elevation variations (e.g. flat land).

 
Information: The contour lines generated using the DTM (Digital Terrain Model) are useful when the area is covered by objects, like buildings. The objects are filtered out for the DTM generation and they do not affect the contour lines based on the DTM.

 

DTM                  Contour Lines using the DTM 

 

DSM                  Contour Lines using the DSM 
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14 comments

  • Juan daniel Marin solis

    No, tengo 3 años utilizando el PIX4D, pero siempre me encontrado con el problema de los arboles, aun en estos días y que el programa evoluciona enormemente y de buena calidad, sigue tomando como curvas de terreno los arboles a pesar de que pones una infinidad de puntos de control en el terreno, sobre todo en lugares donde la vegentacion es demasiada densa.

  • Daniel (Pix4D)

    Hello Juan,

    In case you have a very vegetated area with many trees covering a large surface where there are not ground points, it is difficult for the software to estimate where the ground is and the contour lines might fail. 

    In order to compute the DTM, If the point cloud classification is available, a terrain mask is computed based on the classified point groups. Only the Ground and Road Surface groups are left untouched, the other groups will be "smoothed". If the vegetation area is very large, the "smoothing" will not be very strong (the software will not interpolate that surface as flat)  and the contour lines might contain some ups and downs.

    Let me know if this explanations is clear.

    Thank you very much.

     

  • Carlos Svaldes

    al momento de exportar las curvas de nivel como puedo indicarle al programa en que escala quiero que lo exporte ya que cada vez que exporto a autocad tengo que buscarlo en la hoja de trabajo por lo pequeño 

     

  • Daniel (Pix4D)

    Hello Carlos,

    There is no such option in Pix4D. 

    You can define the resolution which is the distance between two 3D points in the Grid DSM and is given in centimeters:

     

    But there is no really a scale parameter.

    If your contour lines are very small, could it be because there is no GCPs and geotags in your project and the coordinate system is arbitrary?

    Thank you very much.

    Please note that there is a community in Spanish where you can ask questions in spanish:  Comunidad en español 

    Regards.

     

  • PINUCCIO D'AQUILA

    Hello, i have classified point cloud with buildings, but countours line using DTM intersect buildings. What is the problem?

  • Teodora (Pix4D)

    Hi,

    A DTM is a digital representation of the bare earth (or topographic surface), while the DSM is depicting elevations of the top of reflective surfaces, such as buildings and vegetation. Please generate the contour lines based on the DSM, in order to obtain isolines that take the buildings into consideration.

    Cheers,

    Teodora

    Edited by Teodora (Pix4D)
  • Stefano Passeri

    Hi,

    I have a problem with creating contour lines of DTM (my version is not updated, is 3.2.23)

    these are the differences between the DSM (left) and the DTM (right).

    Much of the modeling is correct, but I don't understand what happen in this area

    crossing the 2 model you can see that there is the big difference (in the circle).

    Could you help me understand why, and how to solve it? 

    Thank you

  • Stefano Passeri

    To complete the previous question I add the orthomosaic to see which kind of terrein is it

    thanks

  • Beata (Pix4D)

    Hi Stefano,

    Could you clarify, I am afraid that I do not understand the question.

    There will always be a difference as one output was generated based on DSM and the other one on DTM. 

    Thanks!

    Beata 

     

  • Stefano Passeri

    Hi Beata,

    thanks for your time.

    Yes, there will always be a difference, but the area in the circle it's a street, therefore no substantial corrections are necessary. The DSM (first image on the left) is it correct, I don't understand why the DTM undergoes so big changes. I tried to change also some parameters but the result it's always the same.

    I hope that now my question it's clearer

    thank you

     

  • Beata (Pix4D)

    Hi Stefano,

    That's interesting, but could you attach one more screenshot?

    I'd like to see the profile of your site in the rayCloud view. 

    It looks like this road goes down through a small hillside. 

    Thanks!

    Beata

  • Stefano Passeri

    Hi Beata,

    sorry for the big delay!

    So, the road climbs starting for the crossroads, I indicated the road with the red arrow in the following screenshots

    If you need more indications I'm available and interested to solve the problem.

    Thanks!

  • Beata (Pix4D)

    Hi, 

    Could you please upload your dataset (images) to our OneDrive? 

    I sent you an invitation to your email.

    I'll investigate the issue from our end. 

    Thank you :-) 

    Beata

  • Stefano Passeri

    Hi, I'm sorry, I did't understand how to upload the images to OneDrive, is in this area? I selected Cloud at the bottom... I haven't found the invitation in the email received.

    Stefano

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