5 replies to this topic

[Martin Gamache]

Can anyone provide advice for ranking a large hydrology dataset.

I've got a stream shapefile created by digitizing some USGS topo maps as well as a DEM. I know I could class them based on elevation fairly easily but this seems too simplistic.

I'm trying to rank them so that I can easily assign line weights based on stream order.

Thanks,

mg

[jsanz]

Can anyone provide advice for ranking a large hydrology dataset.

I've got a stream shapefile created by digitizing some USGS topo maps as well as a DEM. I know I could class them based on elevation fairly easily but this seems too simplistic.

I'm trying to rank them so that I can easily assign line weights based on stream order.

Thanks,

mg

<{POST_SNAPBACK}>

Well, it depends on your available software. So, GRASS has modules to categorize streams according to the Strahler categories but if you are on a Windows$ environment maybe you'll find TauDEM usefull but a little bit difficult to work out.

http://hydrology.neng.usu.edu/taudem/

TauDEM works with ArcGIS and MapWindow (this last is free as freedom).

Sorry by my horrible English

BR

[Polaris]

Martin -

I've used Strahler andShreve stream ordering in the past, but lately have done this with good (better) results using flow accumulation. There are some ArcView scripts available that make this fairly straightforward. I'm out of the office for the next few days, but could give you more details early next week if you like.

Eric

[burwelbo]

Martin

In Arc 9.0 there is a tool called Stream Order located in Spatial Analyst/hydrology. You need to ctreate a thresholded Flow Accumulation grid and Flow Direction grid as inputs. It will create a classified grid of stream orders. I think you could then intersect them with your hydrology vector dataset (Attribute Transfer). That brings up a question for me as to how do you create the tapered effect in photoshop automatically?

Good Luck
Bruce

[Martin Gamache]

Fairly easily, you need to select the lowest order...i.e. the end of the small streams, and split the line from the end about 50' add an attribute so you can symbolize the end pieces differently using a different stroke weight and color for example. In illustrator after export you select all these segments and apply the tapered brush to symbolize them. There is probably a way in the GIS to make sure the line direction is correct for the brush as well and if it isnt to reverse the direction, although I'm not sure what it is.

mg

[pghardy]

... That brings up a question for me as to how do you create the tapered effect in photoshop automatically?

<{POST_SNAPBACK}>

For those using ArcEditor or ArcInfo, the new cartographic representations capabilities coming in 9.2 have a framework for 'geometric effects' which can do this sort of thing on the fly. We gave a paper at Auto-Carto2006 last week, which covered using the geometric effects mechanism (with sample user-written effects) to dynamically convert crude linear GIS streams to naturally curved and tapered streams at draw time.

See attachments  streamsA.gif   4.21K   114 downloads and  streamsB.gif   4.23K   116 downloads for before and after shots.

I don't think the paper is yet available on the web, but when it is, I'll post a link to it.