How to model an existing hill without surveying tools?


#1

I’d like to use SketchUp to carve a driveway and stairway into a model of the hill that my house sits on. I don’t have any special surveying tools. How can I measure my hill in real life so that I can model it in SketchUp?

I don’t need perfect accuracy – I’d just like to get close-ish. It’s easy to measure the width of the hill with a measuring tape, but I don’t know how to measure the depth. (If I run the tape from the base (and front) of the hill to the top (which is also the back) that’s a diagonal, longer than the depth.) I also don’t know how to measure the steepness of the slope. If I buy a cheap little protractor, can I do this? How about if I get a free or cheap iPhone app?


#2

Couple of questions. Is the hill grassy or wooded? Is it a uniform slope from the bottom to top? Are there drastic changes in slope along the hillside?


#3

Facing a task with no tools and no knowledge would get most people down, I think, but not you. I must salute your buoyancy of spirit as you proceed into the unknown with a light step.

A protractor is probably the wrong tool. You can perform a simplified level survey of your yard using an inexpensive laser level (I see a cheap one in Amazon for 12 bucks) and something like a yard stick. An assistant would also help.

Set up the level on the highest part of the slope. Call the spot where you place the level your benchmark. Now locate various spots around the yard where you’d like to measure the elevation relative to the benchmark, and measure the offsets of these spots say, south and west (or whatever makes sense) from the bechmark so you can plot them to scale. You might want to number or otherwise label the spots where you will read the elevation so you can record your readings in a log.

Now once the laser is leveled, note the distance above ground of the laser beam at the benchmark. That’s the height of the instrument–bechmark (elevation 0) plus the distance above ground. Now have your assistant stand at each measurement location holding the yard stick on the ground, Shine the laser on the yardstick, and have your assistant read the height of the beam. For each location, height of instrument minus the yardstick reading equals the elevation of the location. Just note the the yardstick height for each spot in the log. You can calculate the actual elevations relative to the benchmark back in the office, say, on a spreadsheet, and then plot them in SU.

-Gully


#4

Here’s a photo of the hill.

http://tinypic.com/r/2wqbdxu/8

Most of it isn’t wooded, though to the right of the current stairway is covered in shrubs. It terminates at a retaining wall at the bottom. I can’t easily stride around on the hill – I’d risk falling down it and off the wall at the bottom. But I can creep along (as I did when I put in some of the plants you can see in the mostly clear area). It’s not uniformly steep, but maybe close enough for my purposes.


#5

Thanks! I understand what you mean about how I could measure heights from a benchmark. I guess I’d have to do it in stages, since I couldn’t reach to measure from the bottom up to the benchmark at the top, but I could see breaking it up and measuring each height change and then adding them together.

What I don’t understand yet is how I’d measure the offset. Say I go from the benchmark to a point that I find to be 3’ lower then the benchmark, and those two points measured along the ground are 9’ apart, but I don’t know the steepness yet. Are you saying to measure 3’ up in the air, from the new point to the benchmark? And then calculate the diagonal using side-angle-side and A squared + B squared = C squared? Or is there a more straightforward way?


#6

I helped out my brother with plan drawings for his new garage. I used the online map service from the municipality to export a map of this site. I was only able to export 2d JPEG, but it included a scale reference which I used to scale it up to correct size in SketchUp.
Then I traced the contours with the Line tool and raised the curves to their correct height in model space. Here I used the online map again to get the heights for the contours.
From that I could use Sandbox Tools, found in the Pro version, to generate the mesh. Using that mesh I could project the site plan and/or areal photo and get a reasonable good representation of the terrain. More than enough for our needs.

If you don’t have SketchUp Pro with sandbox tools you might be able to use some other extension to generate mesh from the contour lines. Maybe one of Fredo’s plugins over at SketchUcation can act as replacement.


#7

You want to locate a series of points in space that define the ground surface. You could divide the area into a grid, say, ten feet by ten feet, and measure the elevation at each grid point. In SU, you would construct the grid and measure a vertical height at each grid point. Or, you could just select a number of points to measure based on how well they describe the terrain, how accessible they are, or other reasons that may strike you as important. In any event, you’ll want to note the measurement point as, say, twenty feet west and fifty-two feet south of the benchmark, or whatever. You need to be able to locate both the benchmark and the measurement points on your model.

If the vertical drop from the laser level to the ground downslope is more than three feet, you don’t have to use a yardstick–that was just an example–use a tape measure if you want. You are measuring from the ground to the laser beam (or actually, you are shining the laser on the tape measure or yardstick and noting the height at which it hits). The laser beam is the height of the instrument. You use the tape measure or yardstick to measure down to the ground–just read the number off the tape.

You don’t have to calculate the pitch of the slope. You are using rectangular coordinates to plot points on the slope, from which you can generate a surface.

-Gully


#8

Ah, got it, thanks very much for all your help! The part I didn’t understand was how to measure where (say) 10’ away even is, since if I measure 10’ along the ground, that might only be 8’ away or whatever because of the slant. But I see now I have to measure in space, along the laser beam horizontally, and then vertically from that point to the ground. I appreciate the patient explanations!


#9

That’s very cool! Sounds like the online map had height data? Or did you have to take height measurements on the land and then correspond your measures with points on the map? If the latter, did you do it pretty much as Gully describes?


#10

The online tool let you query the data for height and all soft of other data. Best of all was that the map service from the municipality is free - at least here in Norway.


#11

Interesting discussion! I grew up holding the other end of a surveyor’s tape for my father- surveying doesn’t have to be complicated, though Trimble has for certain got some very fine precision instruments that can dramatically improve accuracy and speed.

Lots of municipalities share their map data win the public- it is always worth rooting around in the website for your city or county. Usually some great stuff is available.

You could also use our 'Add Location" feature in SketchUp to grab a terrain snapshot from Google Maps. Quality varies widely by location, but you might get lucky and find high resolution data in your area.

John
.


#12

I will be trying a different approach using an iPhone and the Theodolite app, as I don’t have access to a lazer level.

The app is able to measure the angle of a point you aim at, relative to the horizon.

(see ‘elevation angle’ on the right of the screen below).

http://a3.mzstatic.com/au/r30/Purple7/v4/b5/30/04/b530042c-5970-3c1f-0e49-fa86b74fddde/screen520x924.jpeg

I’ll also measure the distance between the point I aim at using a tape measure, and where I take the angle measurement with the phone initially (the benchmark point).

Then in SU, from the benchmark point, it’s possible to plot the points in space using the Protractor tool.

(Apologies for resurrecting an old thread, but I hope this is useful to someone).


#13

Same here but rodman / inspector for city engineers ( Water lines, curb and gutter, streets, sanitary and storm sewers. side walks etc)
Did not like inspection had too many threats from BIG contractors to come across ditch and punch me out specially on back fill requirements on laterals, rolling time on sub base for asphalt streets and slump limits for concrete.