Resolution of Elevation Data

classic Classic list List threaded Threaded
6 messages Options
DanielMartin DanielMartin
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Resolution of Elevation Data

Hello everyone!

I am using the following snippet to grab the resolution of the underlying Elevation data.


  didWork = qry->getElevation(*pt, outElev, 0.0, &outResolution);

My question is, what does outResolution represent? Looking at some github documentation, it only says that the outResolution represents the resolution of the data. But what is that? Meters between datapoints? Centimeters between points?


Thank you!
gwaldron gwaldron
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Resolution of Elevation Data

Hi Daniel,

The value is the distance between two adjacent elevation samples in the elevation dataset, at the level of detail that the query result came from. The units are the units of the Map profile. For example, in a geocentric map, the units are degrees.
Glenn Waldron / Pelican Mapping
DanielMartin DanielMartin
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Resolution of Elevation Data

Awesome!
So, on a geocentric map, if I wanted to get the distance between two adjacent elevation samples in the dataset in meters, I'd just add that to my original longitude value and compute the distance then?
gwaldron gwaldron
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Resolution of Elevation Data

Hmm.. I don't understand your question, can you rephrase?
Glenn Waldron / Pelican Mapping
DanielMartin DanielMartin
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Resolution of Elevation Data

This post was updated on .
Sure! I'm probably missing something obvious.

So, my main issue is that I need to know what the resolution of the underlying elevation data is, in meters. For example, if I have some dted0 data loaded, then I know the resolution is about 900m. If I have dted1 loaded, the resolution is 90m. Etc etc.

So I understand that when I call ElevationQuery::getElevation, I will be getting back the resolution in degrees (as my map itself is geocentric). How would/should I go about turning the resolution in degrees -> resolution in meters?
Would I query some lat,lon point for the resolution of the elevation data loaded there, and then find the distance between that lat,lon point and another point where the lon = initial_lon + resolutionInDegrees?

(I did this, and I am getting back a distance that does not fall within the range of dted0, so I'm fairly certain that is not what I should be doing.)
gwaldron gwaldron
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Resolution of Elevation Data

You can convert from longitudinal degrees to meters with the following math:

double metersPerDegreeAtEquator = mapSRS->getEllipsoid()->getRadiusEquator() / 360.0;
double meters = degrees * metersPerDegreeAtEquator * cos(latitude_in_radians);

Hope this helps!
Glenn Waldron / Pelican Mapping
Loading...