Bcavender

GPS Elevation Data as Terrain Input

Recommended Posts

I am working on a new property where we will need a home and several buildings. Detailed Topo Elevation data seems hard to find as the area is rather rural.

 

Having built a spreadsheet of test XYZ data and importing that into CA/Home Designer worked quite quickly to produce a terrain surface.  Since that worked well, I would like to take a handheld GPS and walk the property and develop a elevation point grid to have a relatively accurate terrain model to design on.   The elevation over the property likely varies about 100 feet.  An minimum accuracy of within 5 feet would work for this project.

 

I would be interested to hear from users that have tried using GPS points to build terrain models and get any info as to how well it worked.  Possibly what GPS units were used as well.

 

I would really appreciate any suggestions and advice about how to gear up for this so as to avoid reinventing the wheel :^)

 

Thank you!

 

Best regards,

 

Bruce

Share this post


Link to post
Share on other sites

Hi Bruce,

 

I have had success with this gps data using this website. http://www.geoplaner.com/

Type in your address or cordinates, start adding waypoints around your property and export in .gpx to import into chief.

It works really well, at least did for me. :)

  • Upvote 2

Share this post


Link to post
Share on other sites

Thanks Michael for the Link.  I will try it when I have time unless you want to do a vid to explain how to use it.

 

It amazes me how some of you guys find these neat web sites that have all this information.

Share this post


Link to post
Share on other sites

yes looks like a great site ,if I can figure it out.

Share this post


Link to post
Share on other sites

Thanks Michael for the Link.  I will try it when I have time unless you want to do a vid to explain how to use it.

 

It amazes me how some of you guys find these neat web sites that have all this information.

 

I'll second that! I tried the site for one of the projects I am working on. Looked fairly accurate from a visual standpoint - no hard elevations taken on this project - not needed. I just added the waypoints in the Map section and they worked easily. I did note that if you move them (switching from Map to Satellite view) they do update but create a new way point in the sidebar list with a "moved" extension rather than the original "added" extension; they also do not delete the old ones. Not sure how that will export yet. Thanks again, Michael.

 

Mike

Share this post


Link to post
Share on other sites

Michael,

The site you referenced is most elegant in its design and performance.  

 

I selected about 500 points in a test area I was fairly familiar with and exported the gpx.    I inspected the gpx output file with a text editor and it was flawless.  Impressive!!!

 

Being new to Chief Architect I had to grope around a few times with the gpx import process, but I finally knocked it out and rendered a decent surface.  Next task is to double check a few reference points with my altimeter to build a little confidence with GeoPlanner/CA.  I also took a screen scrape of what appears to be 1 foot contours out of the CA topo page and superimposed the lines on a Google Earth aerial.  From what I can see and what I know of the land, it came out rather well.  

 

Thank you for the assist in helping me find that tool!

 

I greatly appreciate you taking the time to help!!!

 

Bruce

Share this post


Link to post
Share on other sites

Hey gang,

Glad it worked for you Bruce & Mike. Wow Bruce 500 point markers, that took a few minutes. :)

 

Scott & Perry

Navigate to your lot. zoom in so you can see lot boundary lines.

Place about 100 + markers over your lot or area. Chief extrapolates the contours better with more points.

Then export the waypoints.

Then import the gpx file into chief using the gps import function. Rebuild terrain and presto! 

 

Here is a file that I made about 220 or so points. It is in Steamboat CO.

 

 

waypoints (1).zip

  • Upvote 1

Share this post


Link to post
Share on other sites

Thank you for all the info. That went pretty easy. I was just wondering how accurate  it is. Within inches or feet?

Share this post


Link to post
Share on other sites

Altitude is same as Google Earth, 5-6ft.

 

jon

Share this post


Link to post
Share on other sites

So the base height could be 5 to 6' off. Are the waypoints then accurate to the base within inches? I can't be 5 to 6' off between waypoints. I really don't care about the base being off, but the waypoints ,I do.

Share this post


Link to post
Share on other sites

From WPT to WPT you should be good.(unless the property is on a split satellite path)  It has to do with the satellite pass, when it was calibrated, etc., etc., spaceman stuff that I don't get.

 

jon

Share this post


Link to post
Share on other sites

From WPT to WPT you should be good.(unless the property is on a split satellite path)  It has to do with the satellite pass, when it was calibrated, etc., etc., spaceman stuff that I don't get.

 

jon

It is not true that the elevation data is satellite.   It is mostly LIDAR.(shot from small aircraft or helicopter)   There are different resolutions that are shot, but most of the FEMA flood plain is shot at 3m intervals which is good for about a .5m vert accuracy.    In less populated areas, they dont use such high res.

 

One downside, is the accuracy over heavy canopies is greatly reduced.  They mostly fly these mapping missions in the fall/winter, but the canopy can still prevent good readings.

Share this post


Link to post
Share on other sites

Aaannnddd... we're both wrong; (from Geoplaner website)

 

____________________________________

 

 

Accuracy of coordinates and heights

 

Accuracy of Google Maps

 

Most of the Google Maps are prepared from Landsat-7 satellite images. Landsat-7 was launched in April 1999 and is an Earth observation satellite of the U.S. National Aeronautics and Space Administration (NASA). The accuracy of the derived Google Maps / Google Earth vector data varies from 0.1m in urban areas to 15m in the Anarctica. The derived Coordinates are rounded by the Geoplaner to a precision of 1m.

 

Accuracy of OpenStreetMap

 

The accuracy of Open Street Maps is partially lower than of Google Maps. Especially OSM country roads and walking trails can have deviations of 10m or more. The reason for this is, that most of the OSM data is recorded by volunteers with their GPS receivers and afterwards uploaded to the OSM database. Depending on their GPS receivers and the reception conditions the accuracy of the recorded tracks varies between 3m and 30m. The accuracy of most OSM city maps, however is significantly higher and is comparable with the accuracy of Google Maps.

 

Elevation accuracy

 

The elevation data is provided by the Google Elevation Service, the raw data for that were originally  obtained during the Shuttle Radar Topography Mission (SRTM): The freely available SRTM data consists of SIR-C data from NASA and X-SAR data of the German Aerospace Center (DLR).  The SIR-C data have a height accuracy of about 6m on at a horizontal resolution of about 30m. The X-SAR data should indeed have a higher accuracy up to 1m, but cover only 40% of the earth's surface. Which of these elevation data are actually provided through the Google Elevation API is not known to us. Geoplaner rounds Googles elevation values to a precision of 0.1m or 1ft. This allows to recognise elevation differences between waypoints which lie very close to each other.

 

______________________________

 

jon

  • Upvote 1

Share this post


Link to post
Share on other sites

I LEARNED A LOT TODAY .Thanks for looking that up guys. 1foot, does anyone think its good enough to use for what we do. Could be, of course if I needed anything more I'd get a survey done.

Share this post


Link to post
Share on other sites

I think Its certainly close enough for approximate terrain modeling. 

Its an easy way to make a terrain in your plans.

It used to take me quite a bit of time to get half way decent results from chiefs tools and images of elevation maps from google and county websites..

Share this post


Link to post
Share on other sites

Aaannnddd... we're both wrong; (from Geoplaner website)

 

____________________________________

 

jon

Good info.   I assumed that google maps just used GIS info.   I know that much of them along with FEMA flood plain maps were constructed from LIDAR.   

 

Good info to know.  Thanks for digging it up!

As for suitability for building pads,  I know that good earth info is NOT even close enough to approximate.   Working on a house now where I exported the google earth data and sectioned it to check elevation drops.   Google earth show 17' change in elevation across building pad.

 

I went out and shot it with a rotating laser....and it was 5'.  I have seen this in several cases.   Data is unreliable and pretty much useless.....unless you just generally want to know what way the water is shedding.

 

I either have topo's shot by the surveyor, or I grid off the areas I want to know and shoot my own.   (I shoot my own for my projects, but tell clients if they want accuracy then need to have a topo done and get their surveyor to do it)

  • Upvote 1

Share this post


Link to post
Share on other sites

Hi Bruce,

 

I have had success with this gps data using this website. http://www.geoplaner.com/

Type in your address or cordinates, start adding waypoints around your property and export in .gpx to import into chief.

It works really well, at least did for me. :)

 

Michael, forgive the stupid question but does it matter what

order you enter your waypoints in? Do you stake out the

perimeter and then add salient points inside? Or perhaps

start at one edge and work across the site? Or can you just

click off dozens of random waypoints and the software sorts 

it all out? Just wondering if there is one approach that is

preferable to the others?

Share this post


Link to post
Share on other sites

Rich I actually went around the perimeter first and then made rows up and down on screen. Even added a few randomly at the end to fill in a couple spots.

 

I just tried this to see it again.

open geoplaner and upload the file I shared. It will fill in the points in order of there original clicking order.

Share this post


Link to post
Share on other sites

Hey gang,

Glad it worked for you Bruce & Mike. Wow Bruce 500 point markers, that took a few minutes. :)

 

Scott & Perry

Navigate to your lot. zoom in so you can see lot boundary lines.

Place about 100 + markers over your lot or area. Chief extrapolates the contours better with more points.

Then export the waypoints.

Then import the gpx file into chief using the gps import function. Rebuild terrain and presto! 

 

Here is a file that I made about 220 or so points. It is in Steamboat CO.

Good stuff,  thanks Michael.

Share this post


Link to post
Share on other sites

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now

  • Member Statistics

    27469
    Total Members
    6254
    Most Online
    THDesign
    Newest Member
    THDesign
    Joined