The new website, [www.americanwhitewater.org:8888]
has the option to input coordinates for rapids.
However, we have not discussed what point along a rapid should be used for the coordinates. I am thinking that the coordinates should be from somewhere around the beginning of the rapid, but that can vary with flow. Sometimes I lean towards marking the middle of the rapid. What do others think?

Rapids do not yet show up on the main display map, but once they do, I wonder if they should be marked as a point or as a line segment along the length of the rapid?

With many of the locations that we are marking, including rapids, put-ins and take-outs, the topo maps and ariel photos do not line up exactly. When you place a marker at exactly the right place on the topo map, it will be off some distance on the aerial views. I don't know if the topo view should take precedence over the aerial view or if the gis elevation data might differ from both views.

Our mapping function uses basic icons. We should create our own whitewater related icons for use on our maps. My impression is that it is fairly easy to create custom icons, but I have not tried that yet. Anybody created custom icons for google earth or google maps?



Edited 1 time(s). Last edit at 07/08/2007 11:02AM by pmartzen.

Well, herein lies the can of worms that is opened when we start trying to add extra detail.

For the whole reach, it makes sense to have two sets of lat/long coordinates, one for put-in, one for take-out. If you include coordinates for a rapids, it would seem you should similarly need start and end of the rapids for the coordinates to be truly meaningful.

Trouble is, for many of the reaches, a rapids is really more of a 'feature' at a quite finite location. It has no 'start' and 'end', it is just a spot with a great playable wave or hole, or a single ledge or waterfall, whose start and end are only feet apart (at least in the two-dimensional horizontal plane described by lat/lng coordinates).

Thus, it seems to me that there needs to be provision to enter BOTH start and end, but allowance for them to be the same, or for 'start' to be specified and 'end' omitted, to accommodate 'features' which are detailed which do not stretch out down the river.

1. Where the topo map and the aerial view differ, the aerial view is likely more correct. Therefore, if one can't get the data from being on location with a GPS, it's probably preferable to use the aerial view to get the coords.

2. Most rapids are small enough so that they can be represented by a point (that's how they're depicted in most river maps you see), so I think it's sufficient to use one lat/lon coordinate pair to describe the rapid. In the case of a long rapid, we can use the Rapids function to give the coords for both the beginning and the end of the rapid.
It's likely better to use the coordinates for the beginning, not the end of the rapid. (The intrepid paddler, if s/he has a GPS duct-taped to his/her bow, would prefer to be told that s/he's approaching Brink of Death Falls than learn about the rapid as s/he's hurtling toward the slab rocks at the bottom of the drop.)

Paul,

Regarding your comment, "With many of the locations that we are marking, including rapids, put-ins and take-outs, the topo maps and ariel photos do not line up exactly..." This may be related to the datum that are used to create each of the different maps. i.e. NAD27, WGS84, etc. For example, if different map datum were used to create the topos than was used to rectify the arial photos, then the lat and long coordinates would need to be translated from one datum to the other when the view is changed from topo to ariel photo. Obviously this would be quite complicated to fix.Unless Google provides the photos referenced to various datum?

As for where to plot the rapid markers, I would advocate for plotting them at the entrance of each rapid. If you're carring a GPS on the river it would be nice to know where each rapid starts. Google also provides functionality to include a hyper link in the description balloon that corresponds to each marker. It would be interesting to have these linked to photos of the rapids or camps, etc.



pmartzen Wrote:
-------------------------------------------------------
> The new website,
> [www.americanwhitewater.org:8888]
> has the option to input coordinates for rapids.
> However, we have not discussed what point along a
> rapid should be used for the coordinates. I am
> thinking that the coordinates should be from
> somewhere around the beginning of the rapid, but
> that can vary with flow. Sometimes I lean
> towards marking the middle of the rapid. What
> do others think?
>
> Rapids do not yet show up on the main display map,
> but once they do, I wonder if they should be
> marked as a point or as a line segment along the
> length of the rapid?
>
> With many of the locations that we are marking,
> including rapids, put-ins and take-outs, the topo
> maps and ariel photos do not line up exactly.
> When you place a marker at exactly the right place
> on the topo map, it will be off some distance on
> the aerial views. I don't know if the topo view
> should take precedence over the aerial view or if
> the gis elevation data might differ from both
> views.
>
> Our mapping function uses basic icons. We should
> create our own whitewater related icons for use on
> our maps. My impression is that it is fairly
> easy to create custom icons, but I have not tried
> that yet. Anybody created custom icons for
> google earth or google maps?

Thanks for the discussion and feedback on the mapping discrepencies. I will follow up with some buddies who are more knowledgable on mapping and gps than I. Makes sense that there are different datam is use that don't always line up.



As for where to mark rapids it certainly makes sense to always mark the beginning of a rapid until you get to a rapid that has a completely indistinct entrance that varies by hundreds of hards with flow levels. That is what got me thinking about it. Some rapids have very obvious and distinct entrances, while some don't.

For Wild Wolf Chute on the Kings River
[www.americanwhitewater.org]
it is easy to mark the main drop near the end of the rapid, but deciding where to mark the beginning is very difficult as it is so gradual. The Google maps/earth view shows the rapid it low water, when the main drop is about the only thing showing. Marking that main drop makes sense. But at high flows the rapid is picking up speed 400 yards upstream. I think I will just mark wherever seems most obvious and then clarify it in the text.