From an earlier thread I read:
Last week I discovered that an entire flood planning mapping project was done at grid instead of ground... Someone is performing hydrological calculations and placing flood boundaries based on this data.
Please explain the folly of doing hydrology studies on grid. I work with hydrology engineers. I am not one. My requests for hydrology surveys are grid requests and I have explained the difference to them.
Just curious.
> From an earlier thread I read:
> Last week I discovered that an entire flood planning mapping project was done at grid instead of ground... Someone is performing hydrological calculations and placing flood boundaries based on this data.
>
> Please explain the folly of doing hydrology studies on grid. I work with hydrology engineers. I am not one. My requests for hydrology surveys are grid requests and I have explained the difference to them.
>
> Just curious.
Don't know about Hydrology, but I'm doing a hydrographic job and I can see how anybody can work with ground in those circumstances.
Ralph
I think large scale when the term hydrology is involved. Entire watersheds as opposed to specific little plots.
How significant is the scale factor where you are?
How accurate is the Topo Data? USCG Contours, LIDAR? What sampling interval?
Might be very significant, or it might not be significant at all.
Good post Marc.
Where we work the grid to ground distortion is between 0 to a little more than 100 ppm. The engineers requesting these surveys do not seem very concerned. Trying to predict what will happen when high water comes is kind of which craft if you ask me but the predictions for crest they made turned out ok. Their point to me was that there are variables that greatly exceed any grid to ground distortion concerns.
