Does anyone have any ideas/opinions/baseless ramblings on the relative accuracy of the height data in Anquet compared with the contours on the maps? I know that in very bumpy areas the height data tends to miss sharp ridges and summits etc because of the resolution of the grid (50m IIRC), but in my relatively flat part of the country (northern Hampshire) there are some interesting discrepancies - for example flattish hills reading well over 100 metres, even as much as 115 or 120 metres over a wide area when the OS contours only admit to 90 metres (or 95 on the 1:25000).
In most places the heights agree very well, but I have found plenty of places where this sort of thing happens - usually with Anquet heights being "too high". Many of these places are forested, which makes me wonder whether the heights were collected by radar measurement which picks up the trees rather than the ground, although some are bare grassland. Also, most forested areas show no corresponding jump in height compared with bare ground.
Does anyone in fact know how the Anquet data is derived? It definitely doesn't include building heights - no 100m + readings in London, for example! - but I wonder if tree cover can throw it out somehow?
On 12 Nov 2004 11:10:07 -0800, [email hidden] (Rob Kingston)
Quoted message said:
Does anyone have any ideas/opinions/baseless ramblings on the relative accuracy of the height data in Anquet compared with the contours on the maps? I know that in very bumpy areas the height data tends to miss sharp ridges and summits etc because of the resolution of the grid (50m IIRC), but in my relatively flat part of the country (northern Hampshire) there are some interesting discrepancies - for example flattish hills reading well over 100 metres, even as much as 115 or 120 metres over a wide area when the OS contours only admit to 90 metres (or 95 on the 1:25000).
In most places the heights agree very well, but I have found plenty of places where this sort of thing happens - usually with Anquet heights being "too high". Many of these places are forested, which makes me wonder whether the heights were collected by radar measurement which picks up the trees rather than the ground, although some are bare grassland. Also, most forested areas show no corresponding jump in height compared with bare ground.
Does anyone in fact know how the Anquet data is derived? It definitely doesn't include building heights - no 100m + readings in London, for example! - but I wonder if tree cover can throw it out somehow?
Run the cursor over a lake and see the height fluctuate! -- R o o n e y
"Rob Kingston" <[email hidden]> wrote in message news:[email hidden]...
Quoted message said:
Does anyone have any ideas/opinions/baseless ramblings on the relative accuracy of the height data in Anquet compared with the contours on the maps? I know that in very bumpy areas the height data tends to miss sharp ridges and summits etc because of the resolution of the grid (50m IIRC), but in my relatively flat part of the country (northern Hampshire) there are some interesting discrepancies - for example flattish hills reading well over 100 metres, even as much as 115 or 120 metres over a wide area when the OS contours only admit to 90 metres (or 95 on the 1:25000).
In most places the heights agree very well, but I have found plenty of places where this sort of thing happens - usually with Anquet heights being "too high". Many of these places are forested, which makes me wonder whether the heights were collected by radar measurement which picks up the trees rather than the ground, although some are bare grassland. Also, most forested areas show no corresponding jump in height compared with bare ground.
Does anyone in fact know how the Anquet data is derived? It definitely doesn't include building heights - no 100m + readings in London, for example! - but I wonder if tree cover can throw it out somehow?
Set a route to follow a stream downhill and see how much uphill the stream does on it's journey down
Set a route to follow a stream downhill and see how much uphill the stream does on it's journey down
Then look at the 3D view to see how the stream doesn't follow the line of least resistance (due to the 50m resolution).
Try following the coast path from Langland to Caswell and watch the path suddenly plummet to sea level and back up again as you round Whiteshell Point.
