Forum

Author Topic: GCP Error as function of distance from GCP  (Read 1404 times)

madhavm

  • Newbie
  • *
  • Posts: 3
    • View Profile
GCP Error as function of distance from GCP
« on: January 12, 2018, 06:40:06 AM »
Hey,

We have a few questions regarding GCP error:

- How does error increase as a function of distance from the GCP?
- How should GCPs be placed to meet a certain accuracy requirement? Should GCPs be placed closer together to increase the accuracy of a site?
- Does significant elevation differences on the site require an increase in the number of GCPs?
- How much elevation difference is allowed between GCPs? Is that even a criteria that needs to be considered?
- Is there a mathematical equation that can define error as a function of distance from the nearest GCP?


Thanks,
Madhav M.

cadm8

  • Jr. Member
  • **
  • Posts: 74
    • View Profile
Re: GCP Error as function of distance from GCP
« Reply #1 on: January 12, 2018, 11:53:32 AM »
Generally there is no mathematical answer to your questions.

Quote
How does error increase as a function of distance from the GCP?
Depends on the project and gcp dispersion
Quote
How should GCPs be placed to meet a certain accuracy requirement? Should GCPs be placed closer together to increase the accuracy of a site?
- Does significant elevation differences on the site require an increase in the number of GCPs?
Generally GCPs should be placed to cover the entire site, without big gaps and taking into account extreme elevation changes. Do consider that spreading out a large number of GCPs does NOT proportionally increase accuracy.
Quote
- How much elevation difference is allowed between GCPs? Is that even a criteria that needs to be considered?
No specific criteria, think of your project as a 3D object that needs to be "tied" by various points with GCPs
« Last Edit: January 12, 2018, 12:06:16 PM by cadm8 »

stihl

  • Sr. Member
  • ****
  • Posts: 408
    • View Profile
Re: GCP Error as function of distance from GCP
« Reply #2 on: January 12, 2018, 05:34:34 PM »
From empirical testing I found out that for projects with a GSD of 2.5 cm the maximum distances I want GCPs to be apart is around 175 meters. Beyond that, the model will start to concave.