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Attackpoint - performance and training tools for orienteering athletes

Discussion: setting a control on the side of a large tree

in: Orienteering; General

Jun 17, 2019 1:50 PM # 
Not sure what's the proper way of centering the control circle on the map in the case of a large tree used as control feature, so crowdsourcing the question here...

Jun 17, 2019 1:54 PM # 
Circles should always be centered on point features.

"703 Control point (P)
For point features, the centre of the circle shall be the centre of the symbol. For line and area features, the centre of the circle shows the precise position of the control marker. Controls shall only be placed on points that are clearly identifiable on the map."
Jun 17, 2019 1:58 PM # 
Is it any different for sprints?
Jun 17, 2019 2:01 PM # 
The only exception I can think of would be if it were a sprint map that depicted a tree with an enormous canopy as an area object, and the control was at the edge of the canopy. If you want to shift the circle by a distance corresponding to the radius of the trunk, go ahead, that won't be detectable. But don't shift it by the radius of the point symbol.
Jun 17, 2019 2:03 PM # 
ISSprOM leaves out the point vs area/line distinction, but I think practice has always been that you center the control circle on a point feature and then specify the side in the control descriptions.
Jun 17, 2019 2:08 PM # 
My interpretation of the above rule is that for line symbols you place it on the corner (for example) not some random centre of the line but you dont shift it to show if its inside or outside of the corner.
Jun 17, 2019 2:19 PM # 
There are features in course setting software where you can put a dot where the flag is; does this mean that using that feature is against ISSprOM? Not arguing for or against, just want to know.
Jun 17, 2019 2:34 PM # 
The dot is used in ski-o, but not valid in ISOM or ISSprOM.
Jun 17, 2019 2:38 PM # 
In Ski-O, the controls are placed on trail sections, not at junctions, and there are no descriptions, so the dot is important to show where in the circle the flag actually is.
Jun 17, 2019 2:40 PM # 
Canadian, that's an interesting interpretation, considering the precise location along a line feature can make a difference in route choice. Looking at high-level sprint maps it appears that the circle is centered on the appropriate side when there is a line or corner, making it unnecessary to read the descriptions. As it should be! Competitors shouldn't have to read the control descriptions in order to plan their route.

I recall some Danes, in particular, talking about doing specific training to tell exactly where the center of the circle was on sprint maps, to make sure they wouldn't have to waste time reading the control descriptions.

But to the original question, if the tree is only mapped as a circle as here, then I don't see a problem with following the rule to have the circle centered on it. It will be clear to the runner as they approach whether the flag is in front or behind the tree.
Jun 17, 2019 3:24 PM # 
The circle should be "wherever it gives the most useful information to the runner". So I'm 100% with Cristina that its best to nudge to it off-centre to show which side of the feature its on, especially for uncrossable line. features.
I wouldn't go as far as sherpes photo, for a 2m tree, an honest 1m = 0.25mm shift is readily discernable.
And if I have Canadian as my controller, the "fence" control feature will become "corner of open area".
Jun 17, 2019 3:46 PM # 
ISOM2017: (703) centered if point feature, precise position for the rest
ISSOM2007: (702) precise position
ISSprOM: (703) precise position
Jun 17, 2019 3:54 PM # 
ISSprOM 703 Control point (P): The control points are shown with circles (footprint 24 m). The centre of the circle shows the precise position of the feature.

Edit: guess this does mean center of a point, but to me “inside corner” is a different feature than “outside corner”, and not just a matter of directional difference. I guess that’s why so many of those become “corner of open area” or “corner of paved area” instead.
Jun 17, 2019 5:07 PM # 
If you want to follow the rules ...
The control circle should be centred on the feature. So, centre the control circle on the tree, the boulder, the fence corner, whatever. It is the control description (column G) that tells you where the control flag is located relative to the feature (north side, inside corner, etc).

If you don't want to follow the rules ...
Nudge the control circle a little bit in the direction of the flag (side of tree, inside or outside corner of fence). I'm perfectly Ok with this, but it isn't what the rules say to do.
Jun 17, 2019 5:37 PM # 
ISOM2000 symbol 702 says, "The centre of the circle shows the precise
position of the feature."

I can only see the 2007 competition rules right now, but they state:

3.5.6 The control description. The position of the control with respect to the feature shown on the map is defined by the control description.

The 2009 "Technical Guidelines for Elite Trail Orienteering" states this:

Since the map symbol is larger than the
feature, positioning the centre of the circle on the control position cannot be
precise. The convention in Trail-O is that, with point features, the circle is
centred on the feature symbol and not offset in the direction of a flag which is
on the side or edge of the feature.

I don't know where the "centered on a point feature" guideline comes from, but I find it very clear and convenient. If I see a circle not centered on the point feature, then it opens a whole can of worms as to what it is showing exactly.

I honestly thought this was more clearly defined than it actually is. I have to admit I'm confused.
Jun 17, 2019 6:01 PM # 
Another version of graeme’s test is “what’s more likely to lead to complaints?”

I think you’re unlikely to get anyone complaining that the control location was too obvious from the map, and that they really would have preferred to need the descriptions.

For a fence corner you should definitely shift. For a tree it depends on what it looks like in reality, and shifting might make it less obvious if the tree is small and the side doesn’t really matter.
Jun 17, 2019 6:10 PM # 
usually speakingt, FOOT-O, true-to-scale features - precise position ALWAYS.
non-true-to-scale - precise position when map scale allows, and because latter, it's limited only to sprint courses.
and this relates also for fences/hedges/corners and similar. when it's possible, precise position is a must. bearing in mind contactless punching as a standart, control sites are placed around 1m from the edge and it's 0.25mm on the map and competitor should perceive it looking at the map.
control descriptions serves only for information that isn't available to be represented on the map
Jun 17, 2019 6:22 PM # 
My non-rule-based preference would be to nudge the circle to help the runner see the location if there is one tree in the circle. If there are multiple trees in the circle, center it on the point.
Jun 17, 2019 8:18 PM # 
"precise position" is terrible terminology.
On the map, features can be displaced from their "precise position" for clarity and to respect minimum separations. So if a high fence has its mapsymbol displaced 2m east for clarity, the "precise position" of "fence east side" is slightly *west* of the symbol.
Jun 17, 2019 8:19 PM # 
I just went through the maps from the last few sprint events where I participated. I could not find one where the control circle wasn't 'cheated' a bit to indicate the inside or outside of a fence corner. That makes so much sense to place the circle that way.
Point features. When I have been setting courses such as the ones I set in Florida where many of the trees are huge and I'm going to be putting the flag on the north side of a tree then I interpret it that 'north side of tree' is the actual feature, not the tree itself, so that is where the center of the circle goes.
Jun 17, 2019 8:42 PM # 
When I set an A-Meet sprint a few years ago, I nudged for trees, etc. but the controller convinced me of the error of my ways as the nudged circle sometimes became ambiguous. Of course I did not have any of the inside/outside of the fence traps on the course, so only a step would be lost by not reading the descriptions, not tens/hundreds of meters.
Jun 17, 2019 10:35 PM # 
For an uncrossable fence corner, it's important information. That's a good reason to not use an uncrossable impassable fence corner as a control feature. Pick something near the corner that's unambiguously on one side or the other. Expecting people to read a displacement of 0.25 mm is ridiculous.
Jun 17, 2019 10:58 PM # 
Reading a displacement of 0.25 mm isn't expected. What is expected is actually using your control descriptions when necessary. Reading control descriptions in advance and planning route choices accordingly is (for better or worse) an important part of Sprint orienteering.
Jun 18, 2019 12:49 AM # 
Actually the correct terminology is impassable fence, not uncrossable fence.

I'm with the displacement group for impassable features and you can generally tell from looking at the map which side it's on. Trees aren't overly important. We had a setter for a national relay champs in 2016 displace every control circle on every point feature (including boulders) in a bush event and it looked dumb.
Jun 18, 2019 2:42 AM # 
Graeme, I'm not actually saying I think not displacing the circle when on the corner of a fence is a good thing. I actually think it makes a huge amount of sense to adjust the control circle to make it clearer which side of the fence it's on. However that is not how I read the admittedly ambiguous rule. To not allow it to be adjusted for trees builders etc. but move it for a corner of feature seems inconsistent.

All that said, bmay has a good point. In sprint orienteering reading the control description is part of the challenge. One might argue that it wouldn't be a bad thing if that challenge were removed... I'm not sure where I stand at this point on that particular argument.
Jun 18, 2019 2:43 AM # 
As long as you displace your position once you've figured out which side of the point you agree on (provided it's an impassable argument).
Jun 18, 2019 7:21 AM # 
CD 2018 document:

"The purpose of a control description is to give greater precision to the picture given by the map of the control feature, and to indicate the location of the control flag in relation to this feature, thereby helping the competitor to better visualize the control site. However, a good control is found primarily by map reading. Descriptions and codes can assist in this task, but:
- for Foot orienteering these should be kept as short and simple as is necessary to locate the control."

Centering circle dead on impassable fence corner and deliberately making control description reading essential for route choice is against both "primarily by map reading" and also "simple as necessary" making it a bad control, something to avoid entirely. As I see it, claiming control description reading is essential part of sprint O is just wrong - it's essential only for bad controls (bad sprints).

On the other hand, shifting circle by the radius of the point symbol gives false impression of control positions for route choice. These lead to current practice, center to point feature and use "corner of open area" instead of fence corner like graeme described or if you are laid-back enough you just shift circle at impassable fence corners (and use open area corner if controller complains).

This discussion thread is closed.