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Question for ESRI Arc__ users in British Columbia, how do you get contour lines?

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#1
tonyw

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Hi, 

  I'm using Manifold GIS. Maps i see from offices using ESRI products have maps showing contour lines. It appears these are vectors as different offices apply different colour schemes for contour lnes ( some white, some grey some brown). If received as raster, you wouldn't have the ability to change colours. The provincial WMS server http://www.data.gov....nect/index.page offers contours using this URL http://openmaps.gov....s&version=1.1.1  (layer ID #179). However Manifold doesn't play nicely with WMS servers. 

 

  I've searched the data warehouse https://apps.gov.bc....ub/dwds/home.so  (needs an ID to enter the site) for contours as vectors or raster but none. The closest I can find and use are hillshades, but these don't have contours or elevation labels.

 

  So, wondering how or where you folks using ESRI products in BC get your basemap layers with (vector) contours? Are you buying the DEM packages instead of using free data?

 

thanks,

-Tony



#2
Spencer

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There is a tool called "Contour" to generatae them from DEMs. You should be able to get some data (30m) from The National Map. Other SRTM data you can get from Earth Viewer, or ASTER data from Global Data Explorer. One would just change the contour interval, run the tool several times, then layer the different colored lines appropriately to display them as needed.

 

I don't use QGIS, but I do have it downloaded on my machine. It appears that there is a way to generate contours using it, however.


Edited by Spencer, 11 August 2013 - 09:16 PM.

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#3
Spencer

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Not sure where to get basemaps with the contours on them though, would be interested to learn. But for the States you can get topographic maps and open with Illustrator and remove any unneeded layers.


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#4
tonyw

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Hi Spencer,

  Thanks, I checked out the National Map Viewer http://viewer.nationalmap.gov/viewer/ but it looks like DEM coverage is for the US only and ends off at the 49th parallel. Your tip led me to find this site http://www.geobase.c...cded/index.html  which has DEM data for Canada for download. I'm testing some data now and it looks good. The GeoBase data were derived from data at 1:50,000 and 1:250,000 while the provincial data were derived from working with 1:20,000 mapsheets. 

 

[Update] Given the two scales of map data, there is some discrepancy between the data from 1:20,000 maps and data from 1:50,000 and 1:250,000 mapsheets. There is up to 115 m distance between streams and their guliies on the contour map. At larger scales (1:20,000) the difference is visible. But I'm further ahead than a few days ago. So making progress....


Edited by tonyw, 11 August 2013 - 10:10 PM.


#5
Spencer

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Glad you are making progress.

There is some 30 meter and 60 meter data for BC on the National Map. SRTM is worldwide at 90 meters. There is ASTER too.

Are you trying to map streams, or just contour lines showing the valleys, etc.? Does Canada have an equivalent to The National Hydrography Dataset? That is THE most accurate dataset of streams in the US. I have found errors in the names of streams using the ESRI 2012 data, so I use the NHD.

Good luck creating your contours.

I know there are also subtle contour lines on the MapBox Terrain maps too.

My connection is slow right now, but I am creating a link to a contour map. Is this about what you are after? 5, 10,50 foot contours represented here on an imagery basemap? http://strowbridge.h...com/Capture.png

Edited by Spencer, 14 August 2013 - 06:51 AM.

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#6
tonyw

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Hi Spencer

 Right, I need to map streams though I have that and other layers in the form of shape files that the province makes available for download. It's just the contours they don't offer as vectors for download. Yes, your example is what I'm after with the contours as my basemap. I don't have a license to use Bing or Google imagery in my maps unlike the ESRI users. 

 

  I'll check the National Map for Canadian coverage.

 

Thanks again.



#7
Charles Syrett

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Greetings from Nelson BC! For BC contours, I download DEMs from GeoBase. The elevation data in BC is actually from the 1: 20 000 provincial data. Download the DEM, then use Manifold's 3D tools to create the contours. The contours will be different from the Federal contours, and more detailed.


Charles Syrett
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#8
tonyw

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Hi Charles,

  Greetings from Vancouver. Interesting that the DEM data for BC on the GeoBase site is from BC's TRIM data, that's good to know. I did the process of using Manifold's' surface tools to generate 20m and 100 m contours from the DEM data from GeoBase. The 100 m was to create darker lines at 100 m intervals. I figured an extra drawing layer was faster than thematically colouring the contour lines every 100 m. (I haven't gotten into scripting in Manifold). 

 

  I notice some discrepancy between contour lines I generate compared to those from the provincial TRIM. For instance streams in the provincial stream layer don't run through gullies in the contours I generate. That's probably an artifact of the algorithm in generating contours from the DEM data.

 

thanks!



#9
Charles Syrett

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Tony, if I created a DEM from a vector contour set, then made a fresh batch of contours from the DEM, I would expect the contours to have lots of discrepancies from the original set. Creating 3D surfaces from data has been called a "dark art"! And one of the biggest challenges is to do this is such a way that the contour re-entries match drainage. Manifold's DEST algorithm claims to do that, but my practical experience with it is that it's only negligibly better than plain old TIN. And I always assume a post-edit on creating contours! (Fun but potentially time consuming and budget-breaking.)


Charles Syrett
Map Graphics
http://www.mapgraphics.com

 

Hi Charles,

  Greetings from Vancouver. Interesting that the DEM data for BC on the GeoBase site is from BC's TRIM data, that's good to know. I did the process of using Manifold's' surface tools to generate 20m and 100 m contours from the DEM data from GeoBase. The 100 m was to create darker lines at 100 m intervals. I figured an extra drawing layer was faster than thematically colouring the contour lines every 100 m. (I haven't gotten into scripting in Manifold). 

 

  I notice some discrepancy between contour lines I generate compared to those from the provincial TRIM. For instance streams in the provincial stream layer don't run through gullies in the contours I generate. That's probably an artifact of the algorithm in generating contours from the DEM data.

 

thanks!



#10
tonyw

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Hi Charles, 

  That makes sense, I hadn't thought about it that way, that I was trying to use results to recreate the original dataset. If the original dataset was an irregular array of elevation points derived from airphoto interpretation to yield a DEM with a regular array of points (or rectangles). So going backwards I'll never recreate the original irregular data set. 

 

Still curious where the folks in BC using ESRI products get their TRIM based vector contours? I've searched over the years but don't see it available. I can't imagine the small GIS shops paying $5,000 per mapsheet for TRIM contour and DEM data. 



#11
Charles Syrett

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Actually, I think it's more likely that the TRIM contours predate the DEMs. In other words, the DEMs were created from the contours, not vice versa. That's certainly the case for other government mapping data, such as Canada's NTS and the USGS.


Charles Syrett
Map Graphics
http://www.mapgraphics.com

 

Hi Charles, 

  That makes sense, I hadn't thought about it that way, that I was trying to use results to recreate the original dataset. If the original dataset was an irregular array of elevation points derived from airphoto interpretation to yield a DEM with a regular array of points (or rectangles). So going backwards I'll never recreate the original irregular data set. 

 

Still curious where the folks in BC using ESRI products get their TRIM based vector contours? I've searched over the years but don't see it available. I can't imagine the small GIS shops paying $5,000 per mapsheet for TRIM contour and DEM data. 



#12
Spencer

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Hi Tony.

I know you said you have the shape files for your streams but is it possible for you to extract them from the DEM that you are trying to get the contours from? They should match up better then.

I am unfamiliar with Manifold is why I ask.

Just a suggestion, but if your channels are that far off and you are not comfortable with it, maybe just start from scratch and extract them yourself. I don't know if your program does that, however.

According to my research, SRTM 90 meter averages about 120 meters from reality from centers of traced streams. This average would be better in a more rugged landscape. My study area is eastern Nebraska which is holly, bu certainly not BC. SRTM data is free too..

Thanks for the Geobase link. That was new to me. I did use it to create the contours on that DEM that you saw.

T MAPS


#13
tonyw

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Hi Spencer,

  Yes, Manifold has an extension that works with surfaces (DEM) and it has a tool for finding watersheds and streams. For my finished maps I used the streams I downloaded from the provincial servers at https://apps.gov.bc....ub/dwds/home.so as those stream lines are consistent with other maps the client has. I zoomed out quite ways and the discrepancy between the streams and gullies is acceptably small. If you are looking for some BC data, the site above has hundreds of layers (except contours!). The OCG WMS version those same layers are here http://www.data.gov....nect/index.page, Unfortunately Manifold GIS doesn't play nicely with WMS. 

 

Thanks again for the lead to DEM,

cheers,

Tony



#14
Spencer

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You are welcome.

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