elevation differences between DTMs

[StanislavaV]

Hello friends,

i have two DTMs and two DSMs created from LAS files......

first LAS files were created in autumn

second LAS were created in spring

when i compare elevations between DTM autumn and DTM spring.......differences are minimal, but to and fro are big differences, like -50 metres

same at DSMs..

what could have caused it? may it be caused by noise by scanning or even something else?

thank you so much

[NeilAyres]

Sorry, I am not with you here.

When you say "differences are minimal, but to and fro are big differences, like -50 metres",

is this a difference between the surveys or a difference between the DEM (ground surface) and DSM (includes structures)?

[StanislavaV]

between the surveys in autumn and spring

[NeilAyres]

Well 50m is a lot. Are these from 2 different survey companies?

There is a possibility that one has supplied ellipsoidal heights and the other geoidal.

Better get back to the supplier to check.

Did they use some local control for their ht measurements?

[StanislavaV]

no they are from one company

that deviations are somewhere in one pixel ....somewhere in two.....can it be caused by noise?

[SteveLynch]

what is the cell size?

what about looking at the raw LAS data?

[StanislavaV]

-cell size is 0,5

-can´t see raw las data ...don´t have access to do that

[SteveLynch]

cell size of 0,5 what, inches or miles or ?

🙂

[DanPatterson_Retired]

or maybe ,50 not -50 Steve

[StanislavaV]

0.5 meters