High accuracy without GPS

[MiguelVarela]

Hi,

Anyone knows if it's possible to get a terrain model with high elevation accuracy (around 15 centimetres/ 6 inches) without using a GPS? I don't need to locate the model geographically, just the elevation within the terrain.

I was told that If I use several GCP's  spread along the terrain and know the exact measure between them and their elevation difference between them, I can get a very good accuracy.

Anyone tried something similar or has any better idea to achieve this?

Thanks for your help
Miguel

[Wishgranter]

1. GPS is good for georeferencing, can get desired "accuracy" without GPS, just need properly calculate proper flight that depend on  used cam and lens + good overlap. What is your equipment ? cam and lens ? how big is the area of interest ??   

[MiguelVarela]

Hi Whishgranter,

I'm planning on using a Sony Rx100 III and my area of interest are beaches with many features on the sand. The size is about 1km x 30meters.

I'm planning on flying at around 30meters altitude and 60º oblique angle for the photos.

From what I understand I need to have many ground control points and know the distance between them etc for the model to calculate elevation with enough accuracy. Is this correct?

Thanks for your help
Miguel

[aggieair]

I don't even get 15 cm elevation accuracy WITH known control points using survey grade GPS equipment.

I just use XYZ of a control point.  I have not yet entered scaling differences or calculated differences between each elevation (not sure this is even required?).

[MiguelVarela]

Hi Aggieair

That's not what I'm talking about. Forget the GPS at all.

I'm talking about using a measure tape and ground control points only.
I'm not interested in having my model georeferenced

Cheers

PS: If you are using survey grade GPS equipment (like a DGPS) and cannot get 15cm elevation, you are doing something wrong.... or you are not using "survey grade" GPS but "consumer grade" GPS.

[aggieair]

"If you are using survey grade GPS equipment (like a DGPS) and cannot get 15cm elevation"

To clarify, my vertical accuracy RMSE (when comparing the DEM to the actual Z) is not below 15cm.
The vertical accuracy of the points at time of collection is in mm using survey grade equipment.

Hopefully someone will know your answer.