Topology (again) & Land Surveys
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Ben, What are you using for data? Your own lidar/point scan or someone elses?
Photomodeller US$2595.00 http://www.photomodeler.com/products/default.html
Check out macdem US25.00http://www.treeswallow.com/macdem/, I haven't used macdem, but have had good results with 3DEM which is a windows form of the same. This is primarily used to handle NASA terrain data.
Chris Fulmer from this site explains it here http://www.chrisfullmer.com/tutorials/sudem/index.html using 3DEM.
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Wow how did you even find that link? A classmate and I made that many years ago, and it has not been updated since. hopefully some of it is still relevant.
Chris
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Hi Chris, Google> "3dem" "mac"
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Just to clarify, it's not for a professional application, its for home use. I'm building my own house and the land is far from flat and needs some excavating. I want to get a reasonable appraisal of the topology as a starting point as this will affect the design of the house somewhat. removing earth is not without significant time and cost, so I can play tunes with the design to have minimal groundworks. I also want to consider the neighbours, who would be slightly downhill from the site. So I might have to sink the house down to not make it overbearing on them.
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I haven't run into any issues using the google earth grab. I have not noticed trees affecting topo. USGS will have a topo of your region. http://nationalmap.gov/ustopo/
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Ben,
knowing where you are located would give us a bit more context in order to help you; data quality varies a lot on a global basis. Does your city/county/state have an online GIS where contour data is shown? Even in NZ now some areas are accurately mapped with downloadable dxf files.Also Google data has usually/often has an accuracy of +/- 7metres - it's mainly downgraded NASA data from the early 90's.
Even 'flat' images of accurate topo lines are useful - for instance have you done a search for nearby permit applications? Often these map terrain well outside their project area and then effectively publish online when they put their application in.
Are you near a major highway or railway? They often have their own high quality maps floating around the web.... -
I'm in East Anglia, UK. Also, it is right next to the mainline railway between London to Birminghamm
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why don't you use something like this: http://www.promap.co.uk/pricing.php, there seem to be cheap options and you can always do a screen grab and trace it .
Must remember to assume that free google data is usually only accurate to +/- 4-7metres vertically, whereas info from Promap and even OS is often drawn from LIDAR (laser radar) and is accurate to 200mm or better. Often the best way to do accurate terrain is to trace and loft a surface (using SU) from an accurate paper or screen map.
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Hi Ben,
I'm just passing through this thread but I have found myself in the same position as you with regards to land surveying and sketchup. I have a workable solution to get accurate points into SU and then construct around them.
In my humble opinion the 3d modeller program might not give you the desired accuracy, especially for land surveys. They are a bit like jigsaw puzzels, if you're out in one area then it affects the whole model (and your confidence in it).
I found that google maps data was weirdly inaccurate to model with. I don't know whether this was something to do with the angle of the camera relative to my land. I did verify using three sources (google, laser measure, total station) and the findings proved my point.
In my opinion the only way to get good readings is to obtain the use of a total station, the best you can afford. Then import the data by hand into sketchup using plugins like surveytools.
I use the bearing/distance method of surveying (like spokes off a wheel) but if you have a reflector less TS then you may want to go with point cloud dataHope this helps
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Some good suggestions, thank you all very much. I will try following up to see what works best in my situation, although I feel I will end up with a laser level and quite a few batens hammered into the ground to pick up levels from.
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