Odd point : 無料・フリー素材/写真
Odd point / Johan G
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
|---|---|
| 説明 | This is about the oddest survey marker I have seen, or rather two markers.In the foreground you can see the reflections off a typical Swedish benchmark (sv. "höjdfixpunk", "höjdfix" or most commonly just "fix"), which is used to get the elevation when levelling, as you only measure height differences when you are doing that.On the tag on the witness post, pointing to the benchmark, you can see its number, 815, and the distance to the point, 0.20 metres. For some reason the hight of the point, usually given in metres to the third decimal, has been ground off. It might be because Södertälje town in the recent years changed their hight systems (I heard it was from three separate levelled nets if I remember correctly, to one system, which is very much tightly matched to the current national vertical reference system, RH2000).Behind the marking pole you can see a typical Swedish trig point or traverse point, which is used as one of a few known points when doing conventional surveying (these days as back sights when using a total station, an electronic theodolite with an integrated laser distance meter).What is not in any way typical is having both a benchmark and a traverse point that close to each other.These days this kind of points are nearly not used other than for rare levelling work, and to check that the survey GPS is working correctly. Even if some of the surveying is done conventionally, that is with total station, with back sights usually layed out with the GPS, most of it are these days done with GPS.The GPS used for surveying is a more advanced that the typical hand-held GPS, which shows in its pricing. They can cost as much as a small car. Anyway, they rely on a network of reference stations like for example this one in Leksand, and servers calculating corrections. With that support they can, with enough visible sky, get down to a measuring uncertainty below 15 centimetres (about 6 inches), usually below centimetres (roughly half an inch) and sometimes down to millimetres. |
| 撮影日 | 2013-04-26 07:35:23 |
| 撮影者 | Johan G , Sweden |
| タグ | |
| 撮影地 | Södertälje, Stockholms Län, Sverige 地図 |
| カメラ | Canon PowerShot SX230 HS , Canon |
| 露出 | 0.025 sec (1/40) |
| 開放F値 | f/4.0 |
| 焦点距離 | 16393.44262 dpi |